Tbi swap build thread

[68 TT]

Originally Posted by rfmaster

In retrospect finding a replacement EFI tank (with built-in baffles) is easiest and least expensive route one can take. Follow up question - is it possible to adapt a 1990 burban gas tank (GM14C Tank Dimensions: 28 3/4" x 28 1/8" x 12 3/4" in your 75 blazer? It looks like 75 blazer also used 31G tank (GM14A; 31 Gallon; Tank Dimensions: 28 3/4" x 28 1/8" x 12 3/4"). Filler neck size might be different.

//RF

The GM14C tank also fits the 87 to 91 Blazer so it should bolt right in.

The only problem I have found is that the older Blazers used a smaller fuel filler neck diameter than the newer tanks and the vent hose diameter is different.

I am just going to modify the filler neck and vent tube connection to match the newer tank sizes or pick up a used one from a TBI Blazer that is correct already.

[kcblazer75]

Originally Posted by rfmaster

The problem with fuel sloshing in square bodies is pronounced when there is less than 1/4 tank full. I do not have first hand experience with 30G blazer tanks.
Over the last couple of years I did a lot of research on surge tanks and fuel delivery systems. In one application Ford used lift pump to draw fuel from the tank into a large size fuel filter (which acted as surge tank) before being fed into high pressure FP. Volkswagen used a plastic surge tank - fuel filter part #533 201 511 A on some of their early 80 cars. I bought one of them in hopes of using in my system, but the fuel line size used by Volkswagen was too small (and metric to boot).
In retrospect finding a replacement EFI tank (with built-in baffles) is easiest and least expensive route one can take. Follow up question - is it possible to adapt a 1990 burban gas tank (GM14C Tank Dimensions: 28 3/4" x 28 1/8" x 12 3/4" in your 75 blazer? It looks like 75 blazer also used 31G tank (GM14A; 31 Gallon; Tank Dimensions: 28 3/4" x 28 1/8" x 12 3/4"). Filler neck size might be different.

//RF

Thank RF and 68TT,

I'm considering my options...

It's a 31 gal tank, and it is reletively new.

I had to modify it for this conversion already. I needed a 1/2" line for the filler vent so I had a port added.

I could easily cap the old return and install a 1/2" line between the surge tank and the filler vent tube. But I am worried about the noise of gas falling from the top of the tank while driving.

I could add another 1/2" port with a tube inside the tank to eliminate the noise.

I could scrap my new tank, get an EFI tank, then figure out how to retrofit/re-engineer the filler tube and vent.

I could get a 4-6 PSI intank fuel pump. Expensive! RF, are you using an in-tank fuel pump on yours?

I could engineer a baffle system like 68TT suggested. I think thats beyond my abilities. 68TT, How would you get it tight inside the tank so it doesnt rattle around?

And of course, the cheap way out is to make sure I dont ever let it get empty enough to have to worry about it!

Decisions, decisions..

Keith

[68 TT]

Originally Posted by kcblazer75

...I could engineer a baffle system like 68TT suggested. I think thats beyond my abilities. 68TT, How would you get it tight inside the tank so it doesnt rattle around?

I was planning on using some fuel tank repair epoxy to secure the baffle system to the tank sides & bottom so it doesn't bounce or slosh around. If cut to the right size the legs could be under a little pressure to keep the center pan / ring in place so the epoxy is just vibration & bounce prevention.

I considered separating the tank halves and welding the baffle & pan system in place but that is a whole lot of work that can be avoided by just spending $90 on a baffled tank. In a situation where no baffled tank is available this would be an option. I weld repaired a whole lot of used fuel tanks in the air force so I know how to deal with them and what to expect. I'd like to avoid that if possible though.

I guess I could cut a 12" square access hole in the top of the tank and cut down on the work a bunch vs. separating the tank halves.

[68 TT]

Originally Posted by kcblazer75

Thats great advice RF. I knew there was something wrong with my design, but I hadn't put my finger on it yet. Something just didn't seem right.

Ill step back and think about the options I have.

I'm considering not even putting on the surge tank. Maybe not worth the trouble.

The Blazer tanks are not long and skinny like the pickup tanks. They are about 30" on each side, square, and 12" tall.

I would have to be really low on gas to have a problem.


Anyone else out there with a Blazer...Have you had any problems with fuel sloshing with an in tank fuel pump and no baffles?

Thanks!

Keith

I will be dealing with the same issue eventually as my 67 K10 conversion will be using a Blazer fuel tank just like yours.

I will probably be buying a new TBI Blazer fuel tank with the proper baffles eventually but want to give it a try with the carbureted tank I have now to save some money as my budget is very small.

I may try to build a tank baffle system out of perforated metal that can be installed through the sending unit hole and riveted together. A nice sized center ring around the pickup sock with the return line fed into it should do the trick. A leg heading to each corner of the tank should keep it in place.

[manimal]

Thank You rfmaster
Ok here are my findings...
I checked the resistance of the pick up coil=887 ohms
I unplugged the fuel module and cant hear the pump....??? Should it start with the fuel module disconnected? Because it does not.

[rfmaster]

Originally Posted by manimal

Thank You rfmaster
Ok here are my findings...
I checked the resistance of the pick up coil=887 ohms
I unplugged the fuel module and cant hear the pump....??? Should it start with the fuel module disconnected? Because it does not.

OK - the following checks should isolate fault.
1) Disconnect fuel pump relay from its socket. Locate two pins inside FP socket that correspond to dark green/white - ECM A1 (Fuel pump relay +12V enable) and black/white (ground) (16 or 14 AWG wire). Set DVM to measure DC voltage between those two socket pins. Disconnect oil pressure switch connector (IRC should have three wires Orange / Gray and Brown or orange red/black). You may get SES fault code 51. Just disconnect neg battery to clear for 30 seconds.

Turn ignition key into run position - DVM should read +12 volts for two seconds and then turn -off and read 0 to 0.6 Vdc. If you got +12 volt during POST then attempt cranking - you should see 12 volts as ECM powers up FP relay during cranking!

At the output side of the FP relay there is (some harnesses omitted) an inline fuse link - it sits between fuel module and FP relay. One side you should see Pink/black wire and other side you should have Tan/white -10 or 12 AWG size wires. Wire colors changed depending on OE harness contractor that assembled harness! Try to find it since if it has been overloaded it will be flaky with temperature!

I may have one of them in my collection - just do not have photo handy.

Do you get spark during no start condition???? - VERY IMPORTANT

//RF

[manimal]

Thanks rfmaster, I just drove it down the street(about 2 miles) and back without any problems. I will do these checks in the morning and post the results. Thank You for the help, it's VERY much appreciated. BTW I am not sure about the spark on shut off. The next time it happens, I will check that. Thank you again and I am sorry for the thread hijack.

[rfmaster]

Keith

You need to do a bit more research before turning a wrench or spending a dollar.

Just because I am very curious (not) I did a quick check on GM14C Tank

Rock auto has tank for $89.79
Fuel Pick up Part # SP12L1H Includes Fuel Pump, Sender, Float and Strainer (4 port) $122.79 or you could re-use your old pick-up with new tank.

About noise - I never hear noise of returning fuel - fuel pump makes more noise (engine is not running) and with a mild 350 idling into a pair of Delta 40 rumbling near by - well you can forget about it.

//RF

[kcblazer75]

Originally Posted by rfmaster

Keith

You need to do a bit more research before turning a wrench or spending a dollar.

Just because I am very curious (not) I did a quick check on GM14C Tank

Rock auto has tank for $89.79
Fuel Pick up Part # SP12L1H Includes Fuel Pump, Sender, Float and Strainer (4 port) $122.79 or you could re-use your old pick-up with new tank.

About noise - I never hear noise of returning fuel - fuel pump makes more noise (engine is not running) and with a mild 350 idling into a pair of Delta 40 rumbling near by - well you can forget about it.

//RF

Thanks RF,

Research is what this is all about. Havent done or spent anything yet. I appreciate the reminder though.

The noise I am talking about would occur if fuel was returned at the top of the tank, instead of the bottom of the tank. It would splash like filling a bath tub. That's the situation I would have if I used the filler vent. The stock return line outputs at the bottom, so you wouldn't hear it.

I appreciate the research you did! Buying equipment is always on the table. However, like everyone else, I'm already over budget, and trying to make due with what I've got.

I'm new to posting, and hope I haven't offended anybody, or asked too much.

Thanks

Keith

[rfmaster]

Originally Posted by kcblazer75

Thanks RF,

Research is what this is all about. Havent done or spent anything yet. I appreciate the reminder though.

The noise I am talking about would occur if fuel was returned at the top of the tank, instead of the bottom of the tank. It would splash like filling a bath tub. That's the situation I would have if I used the filler vent. The stock return line outputs at the bottom, so you wouldn't hear it.

I appreciate the research you did! Buying equipment is always on the table. However, like everyone else, I'm already over budget, and trying to make due with what I've got.

I'm new to posting, and hope I haven't offended anybody, or asked too much.

Thanks

Keith

Keith

There is no offense in asking pertinent questions - this is a discussion board and if you look through the threads all sort of questions are brought to the 'table'.

Back to your return line situation - couple of points of interest.

1) Return line should not have any back pressure - if I interpret your post correctly you were planning to install a return line bung into a filler neck. It is do able and I have seen it done before - putting a T into a vent line.

2) The bathtub noise - as I have mentioned before it is really a non issue in a running vehicle. I simply can not hear it in my truck with engine running! Both my tanks are equipped with a three port fuel pick modules - Fuel supply, fuel return and vapor vent (to CCP). The mistake I made during my conversion was to keep original non baffle tanks. I simply did not know any better. I used FG05C (right) and FG05D (left) fuel sending units with external fuel (low pressure) pump.

Interestingly enough return fuel line ports have a check valve that also acts as a fuel spreader (inside the tank) - this is probably the reason why I can not hear noise of splashing fuel! In your case you can probably achieve the same effect with a section of 1/2" ID SAE 30R10 fuel hose perforated (like a Swiss cheese) with many holes acting as a spreader, inside your tank. Note that everything inside tank must be rated for fuel immersion - fuel hose must be SAE 30R10 not commonly available SAE30R9 (fuel injection) or SAE30R7 (50 PSI fuel line).

//RF

[kcblazer75]

Originally Posted by rfmaster

Keith

1) Return line should not have any back pressure - if I interpret your post correctly you were planning to install a return line bung into a filler neck. It is do able and I have seen it done before - putting a T into a vent line.

2) The bathtub noise - as I have mentioned before it is really a non issue in a running vehicle. I simply can not hear it in my truck with engine running! Both my tanks are equipped with a three port fuel pick modules - Fuel supply, fuel return and vapor vent (to CCP). The mistake I made during my conversion was to keep original non baffle tanks. I simply did not know any better. I used FG05C (right) and FG05D (left) fuel sending units with external fuel (low pressure) pump.
Interestingly enough return fuel line ports have a check valve that also acts as a fuel spreader (inside the tank) - this is probably the reason why I can not hear noise of splashing fuel! In your case you can probably achieve the same effect with a section of 1/2" ID SAE 30R10 fuel hose perforated (like a Swiss cheese) with many holes acting as a spreader, inside your tank. Note that everything inside tank must be rated for fuel immersion - fuel hose must be SAE 30R10 not commonly available SAE30R9 (fuel injection) or SAE30R7 (50 PSI fuel line).

//RF

RF,

That is a great idea! I hadn't thought of installing a "Swiss cheese" pipe inside the tank. That would properly allow air to escape while filling, and baffle the sound of fuel return. I will probably use brass pipe instead of rubber (as the filler vent bung I installed is threaded). I can "T" the vent on the outside of the tank, one for the filler vent, and one for the surge tank return.

I'll chew on this for a little while before taking any action.

Thanks

Keith

[manimal]

OK, here are my findings......
Key off; .01 dcv between dark green/white and black/white
Key in run; 12 dcv, does not go off after 2sec
engine cranking/running; .66 dcv
* accidentally touched the tan/white wire instead of dark green w/DVM engine stalled
I cannot find a fuse link-also my FSM says that is only for the "CK" and not the "RV" vehicles. I am confused.....
I then followed the FSM for the test...
I hooked up 12v power to the FP test wire and pump runs.
disconnected the fuel module and removed the 12v to the test wire..key to run, pump does not run.
key on;checked the orange wire to ground I have 12v, then dark green/white to battery -, I have 12v,but when I use a test light between the two I get nothing????(test light is good) NOW I am really confused!
using the test light proceedure, my manual says there would be an open or short in the dark green/white wire or faulty ECM.
SO I continued on based on the DVM reading of 12v @ the dark green/white wire......
again key in run still no FP running.
Reconnected the fuel module engine running,disconnected the FP relay, engine still ran.
Key off, I probed the FP test socket, no power....Factory Service Manual says-NO TROUBLE FOUND.
Does any of this make sense? Cause I am REALLY confused.
Thank You

[rfmaster]

Originally Posted by manimal

OK, here are my findings......
Key off; .01 dcv between dark green/white and black/white
Key in run; 12 dcv, does not go off after 2sec
engine cranking/running; .66 dcv
* accidentally touched the tan/white wire instead of dark green w/DVM engine stalled
I cannot find a fuse link-also my FSM says that is only for the "CK" and not the "RV" vehicles. I am confused.....
I then followed the FSM for the test...
I hooked up 12v power to the FP test wire and pump runs.
disconnected the fuel module and removed the 12v to the test wire..key to run, pump does not run.
key on;checked the orange wire to ground I have 12v, then dark green/white to battery -, I have 12v,but when I use a test light between the two I get nothing????(test light is good) NOW I am really confused!
using the test light proceedure, my manual says there would be an open or short in the dark green/white wire or faulty ECM.
SO I continued on based on the DVM reading of 12v @ the dark green/white wire......
again key in run still no FP running.
Reconnected the fuel module engine running,disconnected the FP relay, engine still ran.
Key off, I probed the FP test socket, no power....Factory Service Manual says-NO TROUBLE FOUND.
Does any of this make sense? Cause I am REALLY confused.
Thank You

Ok lets take it step by step.

1) Take a look at a circuit attached. The RV section is top of the page.
The only major difference between the two is that RV has prime terminal hanging at the end of red wire (under FP relay) and CK have that end terminated at ALDL connector. Otherwise functionally and electrically they are the same.

2) Theory of operation.
Re-install FP relay. Disconnect oil pressure switch connector.
At the oil pressure switch locate orange wire terminal - it must have 12 volts at all times. The fuel pump side may have either tan/white or gray color wire - this is a switched side of FP relay. During POST ECM applies 12 volts at Pin A1 (dark green/wht) energizing FP relay for about 2 seconds. Also at the same time it monitors voltage on pin B2 (Fuel pump signal). FP power-up FP circuit for about 2 seconds and shuts off. This is a normal operation without fuel module.
When you removed FP relay ECM will not see 12 volts pin B2 (Fuel pump signal) which will set DTC 54 (FP voltage low). With DTC 54 set ECM goes into limp mode and depending on calibration it may not apply control signal (A1) during cranking - I simply do not know why, but I have seen this before. What is important is that ECM is able to supply +12 volts to FP relay from pin A1 dark green/wht wire.

Now, with FP relay re-installed connect DVM to measure DC voltage from gray pin of the oil pressure connector to ground. Oil pressure switch is a fail safe mechanism if FP relay fails with engine running. With ign off you should see 0 Vdc, ign into run - you should see 2 sec (with Fuel module disconnected) or 20+ seconds with fuel module connected. During cranking there must be +12 volts.

3) dark green/wht is a low current switched source - supplied by ECM (pin A1). It should not be shorted to ground as it will blow switching transistor inside ECM! Use DVM - do not use test light since you do not know how much current your test light is pulling. Typical FP relay has a coil resistance between 200 and 300 Ohms and pulls less than 100 mA of current from 12V.

4) Take a look at FP test connector (490 red on attached schematic). It is connected to NC contact of FP relay. Under normal conditions, FP relay is powered moving center contact from NC to NO position and with engine running you should 0 volts. If and only if FP relay failed to close and engine is running you will see +12 volts as fuel module or oil pressure switch are supplying power to FP. This way you can establish if you have a flaky FP relay coil or control circuit.

//RF

[Chad77]

Ok 1st of all This thread I have learn quite a bit a big thank you to all!

Just to let ya's know I have read this from pg1 to pg23 whew alot of going on.

OK now on to the Q's .

1. Their is a link to a fuse block If if remember wright anyways the link is dead!

2.Ok I have the original ALDL plug out of the 88 pickup do I just route the wires required for this wright into this plug or is there something to go between IE fuses .

3. Even thoe I read through this front to back and followed the printout where do I hook the Injector power up along with the other power ?

4. I have the single (BIG) relay for the fuel and their is a pink/black wire that comes out of that and goes to a plug their is also a Orange wire and they are both connected to a plug I think this is the oil press plug am I wright.... Bottom look lets see g/w to com p/b to fuse and (plug no clue) b/w ground tie org to tie, What do I do with the red/white?

Here is a reference pic
I was wondering if I could put the senor in the location in the red square?
I have read many different things on the injectors and now confused can some one tell me witch ones these are?


Sorry for the size no clue on how to make them smaller.
thanks for any info.....

[rfmaster]

Originally Posted by Chad77

Ok 1st of all This thread I have learn quite a bit a big thank you to all!

Just to let ya's know I have read this from pg1 to pg23 whew alot of going on.

OK now on to the Q's .

1. Their is a link to a fuse block If if remember wright anyways the link is dead!

2.Ok I have the original ALDL plug out of the 88 pickup do I just route the wires required for this wright into this plug or is there something to go between IE fuses .

3. Even thoe I read through this front to back and followed the printout where do I hook the Injector power up along with the other power ?

4. I have the single (BIG) relay for the fuel and their is a pink/black wire that comes out of that and goes to a plug their is also a Orange wire and they are both connected to a plug I think this is the oil press plug am I wright....

5. Their is one more Q but I need to take a pic so everyone knows what Iam talking about...

thanks for any info.....

Welcome to the thread Chad

1) Few questions first - what are you working on, model, year, etc? Second, what is the year of TBI system that you are using? 88??? Regarding fuse link - you may want to take a snapshot of it and posted. There are several and things changed over the years. So the key to this is to identify what it is, how it works and is it really needed.

2)ALDL connector needs a handful of wires routed to ECM and ground:

Pin A Ground (black/white or black) - make sure that it ties to ground and ECM A12
Pin B Diagnostic (white/black) )
Pin C can be omitted
Pin D SES - (brown/white) very handy if your panel SES light is not working
Pin E Serial data (orange)

3) Injectors need +12V power from IGN circuit - fuse box. The key is to find circuit that is hot when ignition is in RUN and CRANK. I use a BOSCH relay powered by IGN (purple wire that powers ignition coil) to provide separate circuit for injectors. You'll need 10 AMP fuse for circuit protection. ECM has two power circuits. Battery on B1 - use 10 AMP circuit and run to battery (always hot) circuit and the other is IGN On - Pin A6 (pink/black) also use 10 AMP inline fuse for circuit protection. You'll have to find circuit in your fuse box that is hot with ignition on and during cranking!

4) You are describing Fuel Pump relay (FP)
FP relay socket should have orange wire - that goes to battery via fuse link, Gray wire - that wire provides switched power to FP in the gas tank (or inline). Pink Black wire on FP socket is used to prime or test fuel pump. The oil pressure switch usually has three wires: orange, gray and brown. Orange goes to battery, gray goes to FP and brown is used for dash light or gauge. FP socket should have two more wires: dark green and black-white. These are used by ECM to power FP relay.

5) Sure - take pictures. It makes everything easier.

//RF

[manimal]

I just re-read my last post, sorry, I did not mean I grounded the dark green/white wire. I was using the DVM. Black lead to battery ground and red lead to pin A1.
I will go test the oil pressure switch now. But everything I have done thus far, the voltage never shuts off after 2-3 seconds,fuel module connected or not. That is where I am confused.
I am going right now to test the oil switch.
Thank You


BTW should I start my own thread? I feel bad for hijacking this one.

[rfmaster]

Originally Posted by manimal

I just re-read my last post, sorry, I did not mean I grounded the dark green/white wire. I was using the DVM. Black lead to battery ground and red lead to pin A1.
I will go test the oil pressure switch now. But everything I have done thus far, the voltage never shuts off after 2-3 seconds,fuel module connected or not. That is where I am confused.
I am going right now to test the oil switch.
Thank You


BTW should I start my own thread? I feel bad for hijacking this one.

Hmmm. I have never seen ECM not shutting down FP relay. Almost always the opposite - never powering up (due to a bad switching transistor). I have seen my share of bad relays in the past, but stuck and holding and then releasing?!

Regarding a thread - your choice. This thread is a collection of problems and solutions relating to swapping TBI system into early squire body trucks. For conversion I look for 87+ trucks and cars for parts.

I never visit 88+ forum since my rig is 1975.

//RF

[manimal]

OK here are my findings again.
Fuel module connected: oil pressure switch; key off(tan/white didnt have a gray) 0dcv, key on 9.36 dcv for 20sec, cranking 0dcv
Fuel module disconnected; oil pressure switch; key off 0dcv,key on 0dcv,cranking 0dcv
Engine running;fuel module connected; fuel pump test pig tail 12+dcv(actually 13.8dcv)

[rfmaster]

Originally Posted by manimal

OK here are my findings again.
Fuel module connected: oil pressure switch; key off(tan/white didnt have a gray) 0dcv, key on 9.36 dcv for 20sec, cranking 0dcv
Fuel module disconnected; oil pressure switch; key off 0dcv,key on 0dcv,cranking 0dcv
Engine running;fuel module connected; fuel pump test pig tail 12+dcv(actually 13.8dcv)

In you last test it is clear that relay is not energized.

Sanity check - did you check all your fuses on your main fuse panel (IFIK as I do not have FSM in front of me that there are couple of fuses related to EFI)???

Fuel module is providing back up power to fuel pump during POST. Once it is removed no 12V power reaches FP.

Conclusion BAD FP RELAY or FP socket since you have verified that 12 volts is supplied by ECM to the FP socket contacts between dark green/wht and black/wht wires during POST.

Measure relay coil resistance - it should be between 70 to 300 Ohms (depending on OE manufacturer) pins 85 and 86

Can you take a photo of your FP relay???

//RF

[kcblazer75]

I just thought of something that I haven't seen much mention of (if any) on this thread.

If you are installing TBI with the idea that your truck should keep running at high angles, you should consider making sure that your system will shut off in a roll-over.

With a fuel surge tank system installed, like an am doing, there is every possibility that there will be enough fuel in the surge tank to keep it running upside down!

My solution is to install a mercury switch that cuts power to the TBI system if I reach an angle of more than 90 degrees. My TBI ignition system is powered by a single HD relay, so I will just put it between the ignition source and the relay.

I'll have to experiment to make sure that a hard bump or bounce doesn't cause the TBI to turn off.

available from Parts Express - http://www.parts-express.com/pe/show...number=060-275

Lets hear it if you have other ideas.

Keith

[68 TT]

Originally Posted by kcblazer75

I just thought of something that I haven't seen much mention of (if any) on this thread.

If you are installing TBI with the idea that your truck should keep running at high angles, you should consider making sure that your system will shut off in a roll-over.

With a fuel surge tank system installed, like an am doing, there is every possibility that there will be enough fuel in the surge tank to keep it running upside down!

My solution is to install a mercury switch that cuts power to the TBI system if I reach an angle of more than 90 degrees. My TBI ignition system is powered by a single HD relay, so I will just put it between the ignition source and the relay.

I'll have to experiment to make sure that a hard bump or bounce doesn't cause the TBI to turn off.

available from Parts Express - http://www.parts-express.com/pe/show...number=060-275

Lets hear it if you have other ideas.

Keith

Something connected through a low oil pressure sensor (like the Auto Meter warning lights use) would do the trick. No worries about an impact setting it off. If you are on your side or upside down you don't have oil pressure for long.

http://www.summitracing.com/parts/ATM-3241/

http://www.summitracing.com/parts/REB-140-1345/

http://www.summitracing.com/parts/SMP-PS171/

Plenty of different pressure ranges out there to suit your specific engine.

It just needs to be low enough that your cranking oil pressure will turn it off so the truck will start.

[kcblazer75]

Originally Posted by 68 TT

Something connected through a low oil pressure sensor (like the Auto Meter warning lights use) would do the trick. No worries about an impact setting it off. If you are on your side or upside down you don't have oil pressure for long.

http://www.summitracing.com/parts/ATM-3241/

http://www.summitracing.com/parts/REB-140-1345/

http://www.summitracing.com/parts/SMP-PS171/

Plenty of different pressure ranges out there to suit your specific engine.

It just needs to be low enough that your cranking oil pressure will turn it off so the truck will start.

Sorry for the late reply.

That is a great idea. I like it better. A pressure switch is also a great safety in case you lose an oil pump, or lose your oil for some reason (bust the pan on a rock for example). That could save an engine.

Question... This would mean that turning on the ignition would NOT power up the ECM. So ECM would go strait from OFF to start when I crank the motor since there's no pressure until the motor starts cranking. Does the ECM require any "boot up" time to set things up before being ready to start? I know I wouldn't get that 2 second fuel pump hit at ignition on.

Is there any circuit that is ONLY hot when the engine is running, and not with just ignition on? I cant think of one. If I can find one, I could use that to allow power to the ECM when ignition is on, but not started.

Thanks

Keith

[68 TT]

Originally Posted by kcblazer75

I'll have to experiment to make sure that a hard bump or bounce doesn't cause the TBI to turn off.

available from Parts Express - http://www.parts-express.com/pe/show...number=060-275

Lets hear it if you have other ideas.

Keith

One of the comments on that product is that vibration can set it off. Not good for a truck. A pot hole could shut you down.

Another is that they sometimes stick and need a tap to make them work. That would be bad if you were needing it to work to cut off the fuel flow.

[cheepin]

So I still haven't been able to get my rig to start on it's own.I can put a little gas in the TBI and it fires right up then the injectors fire and it will run all day.But once you shut it down and let it sit it won't fire without putting gas in the TBI again.

Do I need to have the fuel pump hook up to the relay?I have it wired to it's own switch and relay.That is separate from the ECM.

[rfmaster]

Originally Posted by cheepin

So I still haven't been able to get my rig to start on it's own.I can put a little gas in the TBI and it fires right up then the injectors fire and it will run all day.But once you shut it down and let it sit it won't fire without putting gas in the TBI again.

Do I need to have the fuel pump hook up to the relay?I have it wired to it's own switch and relay.That is separate from the ECM.

Hey Cheepin

Lets solve your problem.

What you are describing is a classic Fuel Pump Relay or FP relay control circuit failure - malfunction. Oil pressure switch contacts close once oil pressure builds above 4-6PSI and that powers-up FP and engine is supplied with fuel and all is good.

1) Did you verify that your FP come-up during POST for 2 seconds??? It should if FP relay is functioning. Couple of electrical checks you must perform:

a) FP operates for about 2 seconds during POST. A POST is power on self test performed by ECM when IGN key is moved into run position. SES light goes from solid on - blinks off - back to solid on if all is good. ECM also power up fuel pump for about 2 to 3 seconds.

b) ECM supplies +12 Volts to the FP relay socket on dark green wire (ECM pin A1)

c) The black/white wire from FP socket is connected to a good ground.

If you can go through above check list you'll most likely find the culprit.
Let us know.

//RF