My Car 87 IROC TPI 5.0 5speed G92 has a serious misfire when i keep a consistant load on the engine. eg. driving down the hyw at 100kph....when its happing if i give it more gas it stops or let off and it stops....car starts fine idels fine and runs great WOT.....I am 100% sure its an Ignition problem....had it hooked to a scanner while diving timing/spark goes crazy....car has new ECM, Prom chip, Distributor, Coil, Ignition Control Module....as well as Plugs, Wires, TPS.....All trying to fix this problem.....Its Been To 3 GM dealers and lots of other mechanics no one can fix it......Any Help Would Be Great!!!!

 

Don't know if this helps or not, but it might be worth a try to get some good injector cleaner and new fuel filter and give that a try. I would think that if it only backfires with a constant load on it, that would lead to something else though. But since you already changed everything else, it couldn't hurt. My car was acting very simular and I found the eprom crapped out on me.

 

I have the EXACT SAME problem that you do. I posted on this board a couple months ago and it was suggested that I have my fuel injectors cleaned because they might be the problem. I haven't been able to do that yet but previously I had replaced everything that you listed with the exception of the ECM & TPS, all to no avail. I would also love to know what the problem is. I'm planning on replacing the following in a few months (I'm currently in a different state than my car is in):

ECM, PROM, MAF (& relays), TPS, and I'll have the injectors sent off to be cleaned while I install a complete MSD Ignition setup.

I've wondered if 2 things might be the cause of this. 1) Could it be the wiring harness? 2) Could it be the knock sensor and/or spark control module?

If anyone can help this guy and me, please don't hesitate to chime in!!

 

Mine had a real bad miss and chug while driving, turned out to a clogged injector.

 

So would the general concensys here be that it's most likely the injectors that is causing our problem?!?

 

You have already stated that you changed everything from the ignition system which didn't cure the problem. I would look at Fuel, Filter, Pump, or Injectors

 

In my case, I've already changed the fuel filter, twice. The original fuel filter was VERY restricted, but the second one I changed wasn't dirty at all (I had only put a little over 2,000 miles on it). I've checked the fuel pressure at idle and during driving conditions and it has been fine at all times. When the car is doing it's thing, the fuel pressure isn't any different than when it's operating normally. I had the injectors cleaned by running the cleaner through the fuel rail, but I haven't serviced the actual injectors themselves. Like I said, I'll be doing that as soon as I get back to the car along with some other things.

--Chris

 

IN My case im sure its not the injetors they have been checked and I have a new fuel pump and filter........when my car misses the timing and spark go crazy.....I am going to check my pick up coil even though i have a new distributor.....and if it is good then I am pretty sure i have a wiring problem......If any one has info on what wires to check or where in the car they go bad...... or even how to check them......anything would be good.
Thanx

 

I thought it might be the pick-up coil in mine. When I changed it, it actually went away for about 2 days, then it came back with a vengeance. If you are going to check wires (which I might do also since a lot of the main electrical stuff will be out when I work on it) I would check the wires that come off of the 4-pin connector to the distributor. Trace them out and see if you can find anything. Space is real tight behind the engine and it seems like a lot of rubbing might go on back there when the engine is on. If you find anything, please post!

--Chris

 

So I have been saying that its for sure not the injectors.....Because My Timing/Spark go crazy when the car chuggs......But Someone I was talking too said if a fuel Injector or something else is messing up the computor might try to compensate for this by messing with timing or something else......Anyone know if this could happen or not?.....Also If the Ohms are good on the Injetors are they for sure working properly?........and what is the proper Ohms to get when you check them?

 

When I experienced these symptoms it was the TPS.

 

After having a complete wiring meltdown and replacing wire by wire, I found that if the TPS is a little out of adjustment you will have an idle issue before it chugs. True, you should check your TPS adjustment, But if you TPS is bad you will either get a TPS high Error or TPS Low Error from what I have seen or ran into. This will be a soft code on the ECM that will disappear each time you shut off the ignition and will appear generally at a certain RPM. Mine used to trip at 2800 RPM unless I really stomped on it. But that is something you can check using a multimeter and ohm it out.

 

While I have never tested the TPS, I have cleaned the throttle body, set the minimum air, and then adjusted the TPS afterwards to 0.54. The problem existed before and after I did this, and I never checked if it was out of adjustment or not before.

Oh and TPI 5Speed, your friend is right. If an injector is out of spec on the ohms it can trip out the computer pretty bad. The injector driver in the computer can do some screwy things that can be pretty hard to track down. I myself want to test my injectors but like you I don't know what the ohms should spec out at. Also for everyone out there who know, what temp should they be tested at?

--Chris

 

I Tested my injectors (when the car was at running temp) and they were all 17.4 and 17.5 ohms......I think 2 or 3 were 17.4 and the rest 17.5......Is this good bad?.........and does it mean that my fuel Injection is for sure working properly?...............Also a different question...If I was to buy a complete MSD ignition system does it not use the stock spark advance and everything else?.....Because if so I will just spend the $$ on that and stop chasing this problem around.