SARswmr

Well I'm hopefully getting close to solving this. Here's the car/problem. '88 IROC convertible with 400 small block/TPI, mild cam, headers and a different rear end that I haven't identified yet. I've only had the car a week so please bear with me on knowing all the history. The car sat for a year without being driven. After that year the guy that owned it couldn't get it to idle. I bought it, changed the IAC and it idled pretty good. I'm changing the plugs (5 down 3 to go).
So.. it runs great when I get it started (hard starts) and seems to be running perfect with a rock solid idle. Then all of a sudden it starts to stumble and SES light comes on. The first time I limped it home and pulled 7 codes, so I figure some were caused later after the initial problem. So I re-set the codes, drove it later and it ran great, full power range, great idle, and then SES light and falls on it's face. I stopped pulled the codes and got a 33 and 51.
My question is will anything else cause the code 51 besides the Memcal or prom? I know the 33 is maf, I'm just trying to see if the computer is possibly bad first. To add, I reset the codes again, drove it for 20 min or so and ran awesome. I wake up this morning and drive not even 3 miles and Mr. SES shows his face and this time I pull the codes and again 7 or 8 codes.

Idea's ???? Hope someone can help.

SARswmr

I also have a Jet chip that I got for free with the car. It was not installed though. I put it in to see if it helped but it worked for about 10 minutes of driving and SES back on with 7 more codes.

Something I'm not sure about is the chip goes onto the stock one. Does it still use the stock Memcal? So could the prom be good and the MEMcal be bad is my question.

IS there any way to test the ECM itself while it is out of the car?

BTW, code 51 is always present with the others. If that helps.

Thanks

ede

i'd look at grounds, at first i was thinking i'd look at the fuel pump and fuel delivery, preasure and volumn.

SARswmr

One of the books I have "How TO Tune and Modify Chev. Fuel Injection" by Motorbooks (PowerTech Series) says....

Code 51
"Code 51 will be set only if there is defective MEMCAL, defective connectionsto the MEMCAL or a defective ECM.....Therefore, if ay 50's codes are obtained when the codes are pulled, they should be diagnosed first."

which is what I am basing my trouble shooting on.

I'm open to any suggestions..

Thanks

BTW- I have a mounted fuel pressure gauge and pressure is at about 38psi.

SARswmr

After looking on some of the boards I decided to check the numbers. This ECM was replaced 2 years ago and a new prom put in. The ECM is correct but I think the Prom # might be wrong? The # is AKXX 16083268 which I think is for a 350. This car is using the stock TPI which is from the original 305 and I'm still running the stock 19lb injectors.

Does this tell anyone anyting?

The only thing I can't figure out is how it runs so good and then all of a sudden falls flat, sometimes only after 15 minutes and sometimes not for alot longer than that.

Any one?

Thanks

SARswmr

Help....?

NTChrist

Your problem sounds very similar to my father's wife's Buick problem.

As you say, it would run fine for a while, then suddenly cut out while running, regardless of fuel demand, vehicle speed, or gear. A SES light was also on while this was happening.
A neighbourhood mechanic diagnosed the problem (my father's wife didn't trust me enough to touch her car ) as a bad ECM. The ECM was replaced, and the car runs flawlessly now.

I'd recommend buying a ECM from a RUNNING car. Buying one from the junkyard is a crap shoot, as you don't know if the ECM was the reason the car is in the junkyard or not.
Maybe try eBay.

There also may be a better GM ECM that can be used. I don't know if the 350 ECM was any different for the TPI, but for instance a good TBI upgrade is to go with the 7747 ECM for the tunability.
This may be something you want to look into on the TPI/ECM boards.

SARswmr

Well I got a new (used) ECM and all the codes went away, thankfully the 51, except a code 33. Well after a few hours today of messing around I notice my iac adj. screw is all the way out. Which in turn I guess makes the TPS setting different. I tried to re-adjust like this: I unscrewed the adj. screw all the way out until it was barely not touching and then rotated it one and a half turns to touching. Set TPS at .60 and when I drove it I got rid of the Code 33 but my idle is too low. I don't have a working tach right now so can't set the iac by rpm. Any ideas? I think I've almost got this thing licked!!!!

Thanks for the reply

irocbsa

Set the IAC by the method described in the tech article off the main page. The set the TPS by the tech article off the main page. You'll be good to go!