I have a 1985 Z28 Camaro with a 305 TPI. The ECM has a stage 2 Jet Performance chip in it when I bought the car which I never really cared much for.

Two days ago I finally got around to putting the stock chip back in I've had laying around for a couple months. Initial test drive was terrible, but this was because the ECM had to relearn all the timing curves. For the first 20 or 30 minutes it felt like I was driving a V6 LOL!

After the ECM had ample time to relearn everything, I hit a backroad and I have never bneen good at the butt dyno but worse case scenario I will say I see no change over the Jet chip and best case it might have actually restored a pony or two if that makes sense .

But I also noticed that the engine overall, runs noticably worse than with the Jet chip.

There is a problem with my engine I am still diagnosing that will cause it to stumble when the pedal is lightly depressed and stall if it tries to idle from a cold start. With the jet chip, I would hold the idle at around 1500 until coolant temp reached 150F, then I could drive away without any stumbling, code 44 ot stalling. Since putting the new chip in, I noticed it takes a longer amount of time before the engine will even think about running properly.

Today on the way home from work it threw a code 44 while still in the parking space warming it up. So I shut the engine off and restarted.

Now would be a good time to mention a new problem that has been arising. Once out of maybe every 10 starts right at that point where the engine goes from cranking to firing a thump can be felt through the floor and a muffled sounding pop can be heard. This noise is remarkably similar to the backfire the last longblock would make through the intake when it spun a bearing and developed a rod knock. The very first time it did this was about 4 days ago WITH the Jet chip so I'm not blaming this issue on the stock chip. Perhaps this has something to do with my car having trouble cranking, especially when cold?

Anywho, I restarted the engine and at this point It's at 150F. I put the car in gear and take off. I can detect a slight hesitation before the engine revs upon the initial press of the pedal from idle. Not 2 minutes after I've pulled out onto the open road, it throws another code 44. So I turn into a Chevron, honk my horn and shake my fist at the jackass that cut me off as I was turning, and restart the engine again. I pull out onto the road again and I'll be a SOB not 30 seconds later it throws 44 AGAIN! It has NEVER done it this bad before that I can remember. So I pull ionto wachovia restart engine AGAIN and speed through a yellow light to hit the 95 onramp (about 90% of the time it throws a 44 is when It's idling), and make it home without anymore odd issues.

So now onto my main question, since It's still 93 in my tank now on the stock chip, could this be a large portion of what's causing my problem? Or should I say the compounded version of a problem that already existed? What octane would be recommended for a 1985 TPI with bolt on mods? No compression or timing molestation.

 

The required fuel in any car is the minimum octane required to prevent preignition.
Datalogging is the only way you can get a definite answer on that. Most likely you should be fine on 87.
I had hesitation issues on my 88 when it was cold. I changed 2 things at once so I don't know exactly what fixed it but I changed:
Ignition module - tested bad on the bypass
MAF sensor - occassionaly threw a code

No problems since.

 

VirpKlr, I would say that BOTH of these parts on my engine are suspect as it has thrown these codes before. It has thrown a code 43 (Electronic Spark Timing) and 34 (Not sure if that's the rioght code for MAF so whatever the MAF code is). It has only thrown each of these codes once in the entire time I've owned it. What caused it to throw the EST code I'll never know. It just randomly appeared one day when I was scanning codes. The MAF code, however, the one time it showed up was the one time I tried to drive the car before it was warm and hesitation was present.

How did you do the bypass test? Did you just unhook the bypass connector and see how the engine would run?

VERY IMPORTANT: Did your car ever have trouble starting when cold? Did it ever throw a code 44?

 

Nope. Just took it to Advance Auto and had them test it. It passed the first time and then failed the second and third time.

Always fired right up no matter what temp it was. It just had major hesitation issues when cold. Never threw a code 44 either.

 

Hmmm. Because what mine is doing is until It's warm, any light press of the gas pedal will make the engine stumble and DECREASE RPM until you either let off the pedal or press it in further.

I consider the EST a strong possibility, since it controls the timing during cranking until the engine reaches above 400RPM and the ECM takes over. What do you think?

 

Yours is doing what mine did.

I would take your module and have it tested. It's free.

 

I have two extra ignition modules in the basement the PO gave me with the car, so I'm suspecting It's had problems in this area before.

I think a more feasible option would be to take these extra modules and have them tested, and if they pass swap one in and see what happens.

The ignition module is located inside the distributor cap correct? I've never taken it it off before.

As for the hesitation, it evens out once the engine is warm. As the engine temp gradually increases, the hesitation gradually decreases until the point it completely disappears.

 

Precisely.

 

As for the cold start issue, I've made numerous posts, tried tinkering with numerous parts to no avail. I figure it won't hurt to post the video link. This problem started just after we got the new longblock installed. Prior to this the car had been sitting for 6 months in summer heat without being cranked once. The final time we started the beaten down 305 to pull it from in back of the shop, was the first time it exhibited this problem. It was so much trouble to start it killed the starter.

http://www.youtube.com/watch?v=ogLdcBoPLEY

 

Put $10 of 87 in the tank ontop of the 1/4 of 93 that was left. Engine seems to like it. No knocking detected as of yet.

I also went to AA and had them test the two extra ignition modules I had. Both of them tested bad. But TBH I kinda figured that since they had clearly been used, and obviously taken out of the distributor.

 

Looks like you need to test that last ignition module.

 

Getting it tested monday