Need a little help

[Bart_3500]

I've had a TBI system on my rig for about 5 years now and it's always run great. I started to change out the 50 some year old wiring harness with a new Centec harness. It didn't include or have anything to do with the TBI system. After getting it back together I had problems. I know the basics of the efi system and that it needed only a couple three outside leads to work. After a lot of trial and error and some help from this site. I got it running. Problem now is that it's running like crap, very rich and surging from 500 to 1500 rpms. The GM TBI I have is for an 88 ish 350. Last 4 of the ECM is 7747. The main problem I had orginally was getting power to the fuel pump. The builder (custom efis) now out of business ran everything in red and black wires so it was fun figuring out what was what. I did and now I have this running problem. Could I have screwed up the ECM? It appears that the IAC motor isn't doing anything because it's running rich, very rich to the point of burning eyes in the garage. I could sure use some help.
By the way, jumping the ALDL only gives a 12 code and running a steady flash off and on. I thought that meant not lean and not rich when the flash on time and the flash off time were about the same.

[EagleMark]

If the CEL is flashing then that is complete failure and Limp Home Mode. That would be very rich

Turn key on and don't start engine... what is CEL doing?

Surging is very common with a vacuum leak. This would also be very rich.

[1project2many]

If all is right, putting the jumper in the aldl with the engine running forces the ecm into field service mode.

Field Service Mode

On the OBDI ECMs, you can jump 'A' and 'B' terminals on the ALDL while the engine is running.
WARNING! This must be done after the engine is running. This is called "Field Service Mode" and will not harm the ECM.

If the ECM is in Open-Loop mode, the SES light will flash rapidly, about 2½ times per second. If it's in Closed-Loop mode, it will flash about once per second. When in Closed Loop mode, flashing less than once per second indicates the ECM is enriching the mixture above the 128 count base line. Flashing more than once per second indicates the ECM is leaning the mixture below the 128 base line.

Shamelessly cut and pasted from here:http://www.thirdgen.org/techboard/po...43-post23.html

[Bart_3500]

If the CEL is flashing then that is complete failure and Limp Home Mode. That would be very rich

Turn key on and don't start engine... what is CEL doing?

Surging is very common with a vacuum leak. This would also be very rich.

Turning key on without starting the CEL is on solid. It goes out just a second or so after starting engine.
I just checked and there's no vac leak.

[Bart_3500]

With the aldl jumpered (a & b) while running the light flashes about once a second. It should be in open loop as I had just started it.

[Six_Shooter]

So, when you turn the key on, the CEL will turn on for about a second, turn off for about a second, then come on solid?

[Bart_3500]

The truck had the battery disconnected for about 3 weeks. Could this crappy running be a result of that? Running poor until it gets educated again? I don't think so, but thought I'd add that bit of information and ask the question.

[Bart_3500]

So, when you turn the key on, the CEL will turn on for about a second, turn off for about a second, then come on solid?

No, the light is on with the key and stays on during crank. After it starts the light goes out after a second or so. No other lights unless jumpered

[Bart_3500]

If all is right, putting the jumper in the aldl with the engine running forces the ecm into field service mode.



Shamelessly cut and pasted from here:http://www.thirdgen.org/techboard/po...43-post23.html

I was looking at the cut n paste link and saw this
Field Service Mode

On the OBDI ECMs, you can jump 'A' and 'B' terminals on the ALDL while the engine is running.
WARNING! This must be done after the engine is running. This is called "Field Service Mode" and will not harm the ECM.

What happens if I were to have the jumper installed and then started the engine?

[1project2many]

The truck isn't smart enough to learn that much. Although that builder was known for his shortcuts, if it doesn't run reasonably well with first start the engine isn't likely to get much better. Did you bump the distributor? Accidentally remove power from an injector wire? Accidentally pull apart a connection to the red/black harness? Loosen a ground wire?

Installing the jumper first will provide flash codes until the engine is started. The ecm will then enter field service mode.

No, the light is on with the key and stays on during crank. After it starts the light goes out after a second or so. No other lights unless jumpered

Try turning the key off for at least 30 seconds. Then turn on but don't start and note behavior of light.

[Six_Shooter]

No, the light is on with the key and stays on during crank. After it starts the light goes out after a second or so. No other lights unless jumpered

If there is no flash, then you are in LHM, at least in my experience this is a form of LHM. It's more common to see a quickly flickering CEL, but I have had solid CELs over the years.

Try removing the PROM, and re-installing it. This can re-seat the PROM and create a good connection again. Check over all of the connections to the ECM. Even a single pin that is slightly pushed out of the connector, or slightly corroded causing a poor connection can cause all sorts of bad times with electronics. The fact that you say you just re-wired the vehicle suggests that something changed in the way the ECM is now fed, and may be causing an issue.

[Bart_3500]

The truck isn't smart enough to learn that much. Although that builder was known for his shortcuts, if it doesn't run reasonably well with first start the engine isn't likely to get much better. Did you bump the distributor? Accidentally remove power from an injector wire? Accidentally pull apart a connection to the red/black harness? Loosen a ground wire?

Installing the jumper first will provide flash codes until the engine is started. The ecm will then enter field service mode.

T
Over a 3 week period I did a lot of things. To my knowledge I didn't bump the distributor or injector. I'll check that tomorrow. There was no accidentally in the red/black harness pull apart. I had the ECM out several times trying to figure out his wiring to get the fuel pump power. Lots of ground wires removed and as far as I know all were reinstalled.

[ony]

might have bent 1 of them little plug in pins on your ecm.

[Bart_3500]

Thanks for all the thoughts. It's almost 6 a.m. and coffee's on. Then it's off to do battle again. The fact that I have no codes tells me it's something under the hood. That's first then I'll drop out the ecm and play with it. I do wished I had it in a most accessible place, but when all's right there's no problem with where I put it. Up under the dash and with the new harness there's more wires in the way. Oh what the heck I didn't have anything to do today anyway. Yea, right!
Thanks again for your experience and expertise.

[Bart_3500]

If all is right, putting the jumper in the aldl with the engine running forces the ecm into field service mode.

Shamelessly cut and pasted from here:http://www.thirdgen.org/techboard/po...43-post23.html

Check for any vac leak and saw nothing. Air cleaner is off so one valve cover is semi open and puffing out (?) Shouldn't it be sucking in (i.e. from air inside air cleaner and intake creating vac to suck hydro carbons inside crankcase by into the intake?) Oh well, all the power inputs are available at the ecm connector. The grds are all there in their correct spots. In open loop and running the cel is flashing faster than I thought last night. I could have been tired after 14+ hours of working on it. Sprayed the intake with brake spray while running and no intake leaks reported (engine flare). One more thing I can check be back later.