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Old 04-07-2017, 07:10 PM   #1
toddtheodd
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Exclamation Need help / idea - no power and erratic idling

1992 Chevy 2500 5.7 TBI

Already replaced:
all vacuum lines
throttle body gasket (was looking for a vacuum leak, and found one)
fuel filter
ESC
MAP Sensor

Thought maybe the cat was clogged up... cut it off.

Unhooked the EGR solenoid from throttle body, and blocked off that port on the throttle body. Finger checked EGR, and it is opening and closing easily.

Mechanic hooked up a fuel pressure gauge, and it ready 10psi.

When I start the truck, it dies. RPMs jump to 1200, and right back down to dead. If I sit there and blip the throttle... forever... it'll run. As soon as I stop, it dies.

If I keep on it, I can get it into gear, and get it moving (5 speed manual / L-1-2-3-OD). In 1st, it surges pretty bad until I get it moving, and then it has no power. At WOT, it falls on it's face, and sounds horrible. Like the freaking thing isn't advancing. I can't even check the timing with all the stuff hooked up, because I can't keep it running long enough to get under the hood. I'm stuck in the cab blipping the throttle.
It sputters and coughs something fierce at all throttle positions.

If I push in the clutch and let it idle for a second, it dies.

If I take off the MAP sensor, and advance the timing by hand to about 6-8 btdc, truck will "sorta" run, and while still bogging down at WOT, will at least pull strong at part throttle. This is a brand new MAP sensor.

Oh... and quick note... when I put a jumper in A and B of the OBDI plug to get the flashing lights to read the code... no service engine soon light. The shift light comes on and stays on solid.

I'm about to go check the ground wires now.

What the bloody hell else could it be?

The only thing I can think of is the distributor... It was running fine, and then started bogging down real bad on the highway. Like the cat was clogged.
In OD, it wouldn't pull up a hill, and lost speed bad. In 3rd, I could get it to pull at part throttle back up to speed, and then back to OD.
If I went down to 3rd, or even 2nd, and floored it, the RPMs stopped at 3500, and that was it. Nothing more.

Also... if I put it in L, and really give it the beans, it won't even bark the tires. No freaking power.

HELP!

I need this freaking thing running because it is my daily driver. Right now I'm driving my gf's Ferd Taurus... and I can't do that forever. I need my truck. NEED...
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Old 04-07-2017, 10:00 PM   #2
toddtheodd
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Re: Need help / idea - no power and erratic idling

Nobody has any ideas?

Cause this is where I'm at right now.
I have a 1970 Chevelle that I rear ended a person in, that now has the entire front end off of it. I was GOING to fix it... but I need this truck right now.

So... if nobody has any ideas. I'm going to pull the 355 out of the Chevelle, and put it into the truck. Because the motor from my Chevelle doesn't need any of this computer bull**** to run.
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Old 04-07-2017, 10:11 PM   #3
franken
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Re: Need help / idea - no power and erratic idling

Old dumb ideas, but easy...
Open the hood at night in the dark and look for ignition sparks w/ the engine running.
Spray carb cleaner around the TBI and listen for changes in idle. Indicates vacuum leaks.
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Old 04-07-2017, 10:19 PM   #4
toddtheodd
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Re: Need help / idea - no power and erratic idling

Quote:
Originally Posted by franken View Post
Old dumb ideas, but easy...
Open the hood at night in the dark and look for ignition sparks w/ the engine running.
Spray carb cleaner around the TBI and listen for changes in idle. Indicates vacuum leaks.
Yeah... did the carb cleaner around the TBI, and found a vacuum leak. Is why I changed out the throttle body gasket.
Now... no leaks.

Just went outside and checked under the hood. No pretty light show. Nothing sparking or glowing at all. Pitch black.
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Old 04-08-2017, 07:23 AM   #5
sntrym95
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Re: Need help / idea - no power and erratic idling

Hi Todd, I think you'll find the 355/carb swap harder than fixing a TBI motor. TBI is pretty simple to troubleshoot.

Pull the air cleaner off and check the spray pattern from the injectors. 10psi is within spec but a little low. Spec is 9-13, TBI likes it closer to 13.

Test your coolant temperature sending unit: http://67-72chevytrucks.com/vboard/s...d.php?t=425788
If the CTS sends the wrong info to the computer, the computer will try to adjust and may run rich or lean.

Test your throttle position sensor: https://www.youtube.com/watch?v=l30-TNXj9Qc

Test your distributor module. You can remove the module without removing the dizzy. Most auto parts stores can test it for you.
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Old 04-08-2017, 09:10 AM   #6
abig84
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Re: Need help / idea - no power and erratic idling

couple other simple things to check, theres a ground wire that should be on the front top of the intake, make sure thats good and clean

can try a wet test on the coil, get a spray bottle and squirt the coil with water and see if it sparks, same with the distributor cap.

when i bought my 1990 it had a strange running issue it would hesitate and the rpms would always crap out when you were holding speed, luckily i had a parts truck and started changing everything, coil, sensors, distributor and finally i swapped computers and that fixed it.
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Old 04-08-2017, 09:35 AM   #7
toddtheodd
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Re: Need help / idea - no power and erratic idling

TPS - .5v at closed 4.2v at wide open (****tier multimeter... not a fancy digital one)

IAC plug - 20 Ohms resistance between green wires. 50 Ohms resistance between blue wires.
How do I check the actual sensor without pulling it?

Spray pattern looked fine. Like a nice cone when revving it.

I have 20 Ohms of resistance at the temp sending unit plug.
Right now it is 62 out here. I checked the Ohms of the sending unit, and it read about 4500. That is right around 60. I can't keep the bloody thing running long enough to let it warm up... but I will try... and then get a reading and hot to see how many Ohms there are.

abig84 - Can you take a pic of this ground wire you speak of?
What should it be attached to? I see there is a ground wire at the thermostat housing... but it goes into the big wire bundle.

sntrym95 - What is so hard about switching them? Both are Gen1 350's. I pull the fuel pump out of the tank, and run a flexible tube down to the bottom of the tank to make sure I get fuel, and cut the fuel pump wires so that I'm running on the mechanical fuel pump already on the motor.
I can reuse the temp sending unit and oil pressure sending unit for the gauges... as well as the fuel level sending unit.
All I need is a wire from the battery to the distributor to give it spark, and hookup the starter.
All of the crap on the front of the 92's can fit on the front of the Chevelle's.
Only problem I can see is that the mid length headers I have on the Chevelle won't fit in the truck, so I will have to buy new headers (dammit!... 3rd set. This motor was originally in a 72 Chevy truck)

So... besides fuel and spark... what else am I missing for the swap? Motor mounts will line up......
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Old 04-08-2017, 12:24 PM   #8
abig84
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Re: Need help / idea - no power and erratic idling

yep the one on the thermostat, i just went and looked on my 1990. its just a long shot but figured it would something easy to check
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Old 04-08-2017, 07:47 PM   #9
sntrym95
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Re: Need help / idea - no power and erratic idling

"Oh... and quick note... when I put a jumper in A and B of the OBDI plug to get the flashing lights to read the code... no service engine soon light. The shift light comes on and stays on solid. "

This is suspect IMO. Do you have a way to hook up a scanner to see if it can provide any info? Can you find another truck in the junkyard that you can swap the PCM from?
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Old 04-08-2017, 10:42 PM   #10
toddtheodd
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Re: Need help / idea - no power and erratic idling

Quote:
Originally Posted by sntrym95 View Post
"Oh... and quick note... when I put a jumper in A and B of the OBDI plug to get the flashing lights to read the code... no service engine soon light. The shift light comes on and stays on solid. "

This is suspect IMO. Do you have a way to hook up a scanner to see if it can provide any info? Can you find another truck in the junkyard that you can swap the PCM from?
I thought it was very suspect as well.
PCM? The computer / brain?

*sigh* FML...
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Old 04-11-2017, 03:03 PM   #11
toddtheodd
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Re: Need help / idea - no power and erratic idling

Okay... so this is where I'm at right now.

I'm calling all this fandangled electrical computer crap what it is... crap.

I've got a motor that I know runs. That I know only needs a few things to run in this truck, and I'm putting it in.

All I need is a flywheel, water pump, and to figure out which wire to run to the distributor. If my midlength headers fit, cool! If not... oh well. Still easier than chasing down this demon.

From what I've read, the mechanical fuel pump can pull through the one in the tank, and all I need to do is pull the fuse to the electric pump. Can anybody confirm this?
If not, I'll pull the pump off of the assembly, and put a hose there with the sock on the end instead.

The tachometer in the dash is no good since it only goes to 5000rpm, and the motor I'm dropping in redlines at 7000rpm, so I'll put a tach on the steering column.

The temp gauge and oil pressure gauge should still work. So should the fuel gauge.

I'm not going to cut out any of the wires at all. I'm going to tape them all out of the way so that if I ever do decide to go back to throttle body, I can. I just need to keep the wires running for the alternator, AC, and starter. Rest should be pretty pointless.
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Old 04-12-2017, 07:17 PM   #12
Kudzupatch
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Re: Need help / idea - no power and erratic idling

Symptoms sound like mine when one of the injectors clogged.
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Old 04-17-2017, 11:17 AM   #13
toddtheodd
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Re: Need help / idea - no power and erratic idling

Update for those interested...

While I was pulling stuff to get it ready for the motor to be pulled, I pulled the hose off the radiator.

What came out was green at first, but then turned blackish brown. Nasty looking ****.

Looks like pulling the motor was the right way to go.
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Old 04-19-2017, 10:06 PM   #14
fleetweld47
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Re: Need help / idea - no power and erratic idling

as mentioned above these are really simple and reliable systems , but I have found that the distributors have a bad problem with moisture and corrosion . I have seen a lot of the tangs that signal the pickup coils in these dist. break off causing the same problems you are having .
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