How to set timing, 95 5.7L Silverado
 

I just finished a cylinder head rebuild, and now I have a timing setting problem. I put the paper clip in AB on the diagnositc plug in the cab, then set no.1 for 0 degrees. Its running weak at this point, stumbles on throttle up. I stop the engine, pull the AB clip, restart, and the timing stays right where it is. Shouldnt it go advance? It runs rough, weak, stumbles, feels like it flooding out.

If I set the timing just off the timing scale (CCW off the left side)(12 advance?) it runs with power, feels great, etc, but still the computer does not change the settings.

Any ideas. I dont think there are any vacuum leaks.

I got the error codes last night and get a 54. I cant find out what a 54 is (other than one reference to a fuel pump relay, but that was for an 80's truck). And websites list these out? Thanks

Your emissions label should have the correct procedure for setting the timing. I believe you should be disconnecting the “set timing connector”, and NOT jumping the ALDL to set the timing. On a 1995, I think the set timing connector is in the cab on the passenger side, and not under the hood like 1993 and older trucks. After you set the timing, you should clear the trouble code that is set by unplugging the set timing connector.

Code 54 is for low voltage / fuel pump relay circuit.

Here are some web sites
http://www.cfm-tech.com/gm_tbi_trouble_codes.htm

http://www.troublecodes.net/GM/

Hope this helps.
ChevyTech

Thanks for the tip and websites, I'll look when I get home

To set/check timing on a '94-95 5.7L TBI truck you disconnect the IC Bypass wire from the distributor by disconnecting the "set timing" connector located under the dash, in the ECM harness. It's a Tan&black wire. Doing so should set DTC 42.
And, yes, your timing should advance as soon as you reconnect the connector.
Roger

I found the tan/blk wire as sone as I pulled off the glovebox, and it was obvious since it was wrapped by itself on the outside of the computer cables. I pulled it apart, set the timing, turned off the truck, and reconnected it, and then the timing advanced almost to the end of the timing marks.

Thanks for the help.

Now to my next problem. I can hear the TBI "howling" on accelleration. It didnt used to do that, its a sound I would remember. And at higher speeds like 50-65 the engine is surging somewhat. I can feel the rapid power pulses like 2 a second or so. Thats new. I checked the connectors on the engine, they all seems intact. I didnt crawl under to the O2 sensor yet. I dont find any vacuu leaks, or hear any either. I have heard about ground problems. I put the temp probe between cylinder 1 and 3 in with teflon sealant, and this probe only has a single green wire, so maybe it does not have a ground path.

Any insights appreciated.

The "one-wire" temp probe is for the temp gauge only, and does not go to the ECM. If your temp gauge is working, you have a grund path. The engine coolant sensor for the ECM is located on the intake manifold, next to the radiator hose. This sensor has two wires and both go to the ECM; one is signal and one is sensor return (does not go to chasis ground).

I drove the truck to work today and it doesnt have the hill climbing power it did before the head rebuild. I am sure this is a computer/sensor problem and not a cylinder head problem. I was seeing real noticable power improvments before I set the timing "by the book" to 0 degrees. I had set it manually to beyond the timing marks at that time(12-14 degrees?), with no noticable pinging. Now the timing at idle set by the computer is just off the scale. I can move the timing up but hesitate to do this.

Thanks for the info about the gauge temp sensor and the other one on the intake. I will get under the truck and look at the O2 this afternoon, and then try some propane to the base of the TBI to look for a vac leaks there, and ground wires will be checked again.

Update: I advanced the base timing from 0 degrees to 4 degrees (next notch on scale). I was getting a code 42 ECM problem of some sort and a 54 fuel relay voltage problem. Today on arriving at work I didnt generate any codes. So timing increase has fixed these somehow.

I am trying to connect my computer to the ALDL connectors using WinALDL. Having trouble with the data, not sure if this is an old 160 baud or newer 8192 baud ECM. I also dont know which transmission I have or if my ECM controls both engine and transmission. Need to find out how to tell.

On a 1995 your automatic transmission is controlled by the computer, and it is an 8192 baud system.

Thanks for the info. I suspect you're right. I could not detect any data using WinALDL. I'll have to try the TuneCat or other freewares out there and build the interface using the MAX232 chip, which is a lot more complex, but its all in the electronics junkbox, I think I even have the chip.

I still dont know what transmission I have, or the engine "vin letter" , what does vin K vin J vin P refer to? Its a towing pkg truck with dual radiators, 411 rear, so its a 4L60E or 4L80E I think. I need these to detemine the ECM protocol set.

Being able to see the online data will be really cool. I might even try to interface it to my palm smartphone, like I've seen on the web. The 8khz data could be used to modulate an infrared LED in the cab and use the palm infrared port to transport the serial data in. Maybe its alreay been done.

Thanks again

You're welcome

Use the “RPO” codes in the glove box to determine which transmission you have. These are possibly the right codes for your truck.

MT1 - TRANSMISSION,AUTO, 4 SPD, THM 4L80 -- E

M30 - TRANSMISSION,AUTO 4 SPD, 4L60E, ELECTRONIC

Here are some sites to look up what the RPO codes mean.
This is a good site
http://www.wiu.edu/users/muwtj1/me9-nc6.txt

This site only list up to 2004
http://www.gm-trucks.com/RPO_2001.shtml

Some codes on this site have less info.
http://www.geocities.com/n1qcr78/rpo.html

Your dtc-42 was probably set when you disconnected the tan/black wire to set your timing. It generally takes 50 re-starts to clear stored DTC's--or remove the battery cable for about 30 sec.
I beleive the 4L80E has two speed sensors versus one for the 4L60E. Both trans have one on the tail shaft or transfer case, but the 4L80E also has one some place on the torque converter housing.
If you look at the ALDL, there will be a connector in pin-E if 160 BAUD, or one in pin-M if 8192 BAUD.
The classic symptom of a vacuum leak at the base of the "TBI" is highe idle.

Thanks for all the help. These are the things I learned today, about RPO codes and I also found I was wrong about some things. I have the following:
L05 code=5.7L TBI
GT4 code=3.73 diff
M30 code =4L60E trans
NA1,NA5 code= <8500 GVWR, Federal

I'm going to pullput the computer and look for the PCM id number, I think its 1619747, but I'll find out. I'm sure of the 8192 now, I got 2 Max232 chips out of old instruments at the plant today, so i'm going to build up an interface

Thanks

Here is what I think your truck has:
ECM part number -16197427, ECM family - P4, 95 GM trucks 4.3L, 5.0L, 5.7L 4L60E

Check this web site
http://www.diy-efi.org/gmecm/ecm_info/

Keep us informed on your progress.

ChevyTech