I got a 1989 Iroc-z28 with the L98 350ci TPI motor. We bought it 2 years ago and it was running ok then, but we have done a lot since. Currently the upgrades we have done, at least off the top of my mind are: AFR 195 heads, Hooker long tube headers that go to a 3in flow master exhaust, New Holly throttle body, new injectors, new high flow race fuel pump, new lifters, new rods, and some other stuff I can't remember.

The original problem started when we tried to do a cam job on it (hence the new lifters and new rods), but the new cam was way too big, and we went back to stock. When we got it running again, it had a hard time running until we put a new chip in it, then it seemed to idle fine. We just did timing today so it is at 6 degrees before TDC. It seems like it idles ok now and revs, but it will eventually die out in a low idle. On the road, it misfires like crazy and sometimes backfires. Sometimes the engine will shut off for a second and then kick back on, especially while accelerating. We are very confused on what's going on and need help. I need to get my car back to a drivable condition soon and this is what is holding me up currently. I appreciate any advice that you guys might have.

A side note is that the engine runs very hot and has burned quite a lot of stuff. I don't know where that is coming from, so any advice there would help.

 

Datalog with tunerpro rt ?

 

I have no idea what that means.

 

Ask whoever tuned for you. you need datalog and refine your tune.

 

We bought a chip off the internet because nobody can tune these chips around here. The tech is too old for any mechanics to work on. I might end up paying hawks for a new one.

 

Plenty off information in the diy tuning section $6e tuning.
i don’t know if hawks tuner does datalogging but you might check that out before purchasing anything.
moates.net has everything needed to datalog and burn as well as suggested tuners.

http://support.moates.net/obd1-gm-commercial-tuners/

 

Yeah none of those tuners are no where near where I live. So that doesn't work.

 

It doesn’t need to be live to get data and tune properly. Might do some homework before you buy from anyone the first purchase didn’t seem to work out to well for customer support.

 

Sounds like some mechanical things may be wrong to.
plug wire routing ok and valves adjusted right?

 

We set the valve lash multiple times and have checked all the plugs

 

Is the timing retarded? Did you unplug the EST connector when setting the timing?

 

As said in the post, we set the timing for 6 degrees before TDC. We tried unplugging the EST, however it seemed to make no difference as I dont think its the right cable. We went back further into the wire loom and found the brown with black stripe cable that should be the EST and made a connector there and disconnected it for timing. We are probably doing something wrong there. I will try to take a picture after I am done with my shift at work.

 

Timing will go from advanced to retarded base when you disconnect the correct est wire by blower housing.
btw what injectors are you using ?

 

I am the other person working with V8lover on the IROC. The injectors are Bosch 22 lbs https://www.ebay.com/itm/283557817853

The timing was set to 6 degrees BTDC after warming the engine and then the tan wire with the black strip was disconnected.

The chip is a stage two Hypertech 128922 https://www.summitracing.com/parts/hyp-128922#overview

We have a Holly 112-507 58mm throttle body: https://www.summitracing.com/parts/h...07?seid=srese1

We will install new engine block grounds and clean and check other grounds. Will also check the spark plugs (which are new)

Fuel pressure was over 40 psi at the rails (I am going to check it again)

Unplugging the MAF made no difference. I am going to try unpluging the TPS and IAC (both were new)

Seems to be bogging/misfiring when under load

 

You guys really need a datalog, I’d guess high int/blm
especially since injector offsets aren't correct. Btw on some of the holleys they never machined between the iac passage and throttle body bore. A 3/8 hole needs to be made for vacuum or modify throttle body. This can effect idle and deceleration.

https://www.thirdgen.org/forums/tpi/...fferences.html

 

Here is an update.

I connected my Actron CP9690 code scanner and originally had four codes:
(45) Oxygen Sensor Rich Exhaust Indication
(36) Mass Air Flow (MAF) Sensor Burnoff Circuit Problem
(33) MAP Sensor Signal Voltage is Too High
(22) Throttle Position Sensor (TPS) Signal Voltage is Too Low

So, I cleared the codes by disconnecting the battery for a couple of minutes
Re-calibrated the IAC, then readjusted the TPS for 0.540 VDC
It ran a bit better and I was able to drive it for about 1/2 miles before the rough engine started again and the codes (45) and (33) occurred again.
I checked the MAF burnoff relay and saw that the wiring at the connector was frayed, so I ordered a new connector pigtail and relay,
I also order the MAF power Relay. Its connector wires were fine

I tried to run the engine for about 10 minues with the air duct removed so I could look into the MAF just after the engine turned off. I did not see the red glow of the slef cleaning element.
I swapped the MAF for another old one (Bosch) but the same results. Next I will measure voltage at the MAF connector after puttung 12 VDC to terminal "G" of the ODBC port

Vacuum is low (around 15 lbs at idle). I have not checked the fuel pressure yet.

I was initially able to get a data stream on the Actron code reader, but was not able to do so on subsequent tries.
I ordered the Moates cable for data logging and will use the TunerPro RT when it arrives.

 

Alright gang, we were able to fix the misfires, it was a matter of wiring issues to the knock and oxygen sensors that was probably confusing the computer. Now we have a new issue, The engine idles high and acts like its under throttle continuously when driving. Its weird and kind of a pain as you are basically trying to brake against the transmission. Anyone know how to fix this.

Good news though is the motor is very strong. Was able to do a little standing burnout in a parking lot no problem.