Hi all,
Im experiencing some problems with my 86 IROC now. It has a 305TPI with the mods in the sig. The mods were all done recently.

The problem Im having is that the car is very difficult to start in the morning. It will turn with no problem, but will not run on all cylindgers and will pop hard in the exhaust. It will try to start immediately, but will only run on some cylinders and only if I keep varying the idle around 2-2500 rpms. If I hold the throttle steady at say 2200rpms, it will just die.
Then, when putting it in gear, it will "shift" very hard (there is enough oil and the filter is new). When starting to drive it will run, but rough and still "pop" in the exhaust.
Once the car heats up to normal operating temperature, it works just fine, runs smooth and shifts smooth.

The other problem Im having is when I floor it. It can be from a dead stop, or after a kick-down. It WILL throw codes, and when checking them, it shows 42, 43 and 45.

The one thing I know Im having problems with, is the alternator. The voltmeter is constantly bouncing all over the place. I went and got a brand new one today, but have not put it in yet. Can this be related to the problems...?
I have also lately started using 93 octane instead of 89 - because I thought it would run better. Could that be a cause...?

Any and all inputs, ideas or thoughts would be very much appreciated.

Thanks!


Ken

 

Popping in the exhaust = unburned fuel/air mixture = one or more cylinders not firing

Take a good look at the spark plugs after a cold start and letting it run for about 60 seconds. If they're gasoline-fouled, then it's too rich.

But it sounds to me like you have several problems. The popping in the exhaust and rough running sounds like ignition; look at the plug wires very carefully. Once you get that solved, move on to the next issue.

 

Yeah, I was thinking that too - but the wires and plugs are all new (about a month old), and the wires are steelbraided and in wire looms, so I think they would be alright. However, I guess it might be possible that one is loose or something?
Also, I checked the codes in the FAQ, and I think two of them were related to ignition problems. Could that be caused off the faulty alternator?

And, one thing I forgot to mention in the initial post - I still have the stock chip with these mods, could that be a possible cause of error?

Thanks a lot for the inputs!


Ken

 

Anyone else have any inputs on this one? Im really stumped and need to get my car running straight.

Thanks,

Ken

 

Ken,

Your modifications list replacement heads and cam. What is the cam profile? If the LSA is too tight and the overlap is too great, the ECM may not like the cam. The one advantage you have is that you are using a MAF instead of a MAP. The air metering is very precise and fuel control should be fairly close. Remember that the ECM expects some other key inputs as well, like CTS, TPS, and EST information. Make sure the TPS is correct, and that the TB is set at the correct minimum air position (or close).

Since your afterfire may be ignition related, you might want to test the wires, cap, and rotor. A megger is great for this, but not many people have them lying around. I lieu of that, temporarily switch back to a "normal" set of wires, but don't bother with the looms. I've always been suspicious of the designer plug wires masking problems, and the steel overbraid is just a ground path in a pretty wrapper.

The DTC 42 is for a problem with the HEI amplifier/switching module. The 43 is an ESC error, and the 45 is a rich oxygen sensor (which is the reason for the afterfire in the exhaust. Repair the ignition problems the the 45 should go away.

A failing alternator may be causing problems. If one of the diodes is shorted, you could be generating an AC component that is confusing the ECM. The GM spec for AC on the system is no more than 2V P-P. Since the signal levels involved are so low, I'd be afraid to see much more than ½ volt and expect the ECM to operate normally. Since you have a new alternator in hand, install it. That may clear up some of the ingition problems, too.

 

Inside the eprom, voltage is very important. There is a table called "Injector Pulse Correction vs Battery Voltage" in both MAF and SD eproms. Most SD guys have to use this table to make corrections inside their eprom if they are running a fairly stout cam (which screws up the MAP readings) and need to make a "tweak" to get a good idle. At idle you typically run less voltage than in normal operation, so this is the approach often taken.

Further, with my underdrive pullies I get less voltage than say above 1,200 rpm. I had to modify this constant to obtain perfect mixture (BLM/INT @ 128/128); especially when idling. In your case, the alternator is causing erratic voltages which the ECM is trying compensate with the "Injector Pulse Correction vs Battery Voltage" but the table is not "perfect" (as many have found).

In your situation I do not recommend altering the eprom, I am only trying to explain what is happening inside the eprom when you have erratic voltage. The solution is to replace the alternator so you are getting consistent voltage where the eprom is more "finely tuned". Only if you have underdrive pullies like I do and need to alter these constants (because it is part of my normal engine opertion) would you even consider altering the eprom. You'd be fixing a "symptom" instead of the "problem".

Also, I agrees with Jeff that you probably have "multiple problems" such as your ignition module. I suspect that replacing the alternator will help but not eliminate all problems. If you still have more problems, then look at replacing the ignition module in your distributor.

Lastly, with the error codes you have, your car has gone into "Safe Mode" (if it was "Limp Mode" you'd barely get out of your own way). In "Safe Mode" the ECM still operates, but it overrides many parameters (like desired idle and tends to make the car excessively rich on purpose) and may ignore certain sensors. The whole purpose of "Safe Mode" was so you could drive it to the Dealership to be fixed. "Limp Mode" was so you could safely pull over to the side of the road.

I only mention the difference between "Safe Mode" and "Limp Mode" as I have found 90% of the time people think they they are in "Limp Mode' when they are really in "Safe Mode". I've been studying this recently and have found it much more profound than I ever thought. Like SES codes triggering fans to operate, forced idle, overly rich open loop operation, etc.

 

WOW!
Thanks a LOT for the very thorough and good explanations.
I am on my way out to change the alternator in a few, and I will let you know how it goes. The fact that you are stating regarding the sensitivity to the voltage, makes me believe that it can help resolve some of this, because the voltmeter (realizing it will not be real accuate at readings like this) is litterally varying between peaking out and go all the way down to zero with a high frequency.

The cam I have is the following:
http://www.compcams.com/base/process...Known=12-256-4

Regarding the eprom, Im a bit confused about that - simply because there are SO many opinions on it, and I don't have my own LOL. Jokes aside, some say HAVE to get a custom burned one for my car to utilize the mods that I have, while others again say it is not needed. I'd certainly rather not spend $350 on a custom chip if it won't do anything for me, but if it will have a positive influence on the mods, then by all means. But basically you all mean that I don't need it once I get these quirks worked out??

Thanks again for very helpful inputs!


Ken

 

The new alternator is in, and the car started right up! I'll have to give it a couple of days to fully prove that it is cured though LOL, but it looks good so far.
The car also seemed to run smoother when warm than what it was before. I also tried to give it some kickdowns etc, but it did not throw any codes!
The only thing left so far to complain about, is the very hard shifting while cold.
How will the trans act if the converter is about to give up? Any way I can find out if that is the problem? The car still has the stock converter.

Thanks,


Ken

 

Bad news!
Today it was the same starting problem.
So, where do I go next to figure that out...?
One thing I have noticed though, if I give it a can of injector cleaner, it seems to be more willing to start. Could it be that the injectors are bad? If that is the case, why would it go away once the engine reach normal operating temp?

Thanks,

Ken

 

Ignition Module in the distributor.

 

Well,
I got the new ignition module in, and it seems so far that it somewhat helped, but it did not solve all problems.
The car is still difficult to start in the morning, it will misfire and only run if you can keep it at 2000rpm or higher. It also needs to "vary", meaning that if I hold it steady at 2000, it will also die, but if I keep "pumping" it at 2-2500 rpm,it will run even though it is rough.
Then, once it is warm, it runs fine.
The only error code I've gotten now is 43, which come only if I accelerate hard, not neccessarily WOT though.
I saw in the FAQ that 43 is Low voltage on timing unit, what can that come from? And where does the timing unit get its voltage from?

Thanks a lot for any help that can help me figure this one out.


Ken

 

Ken, I've worked on 3 seperate code 43's, twice it was (for sure) a bad knock sensor.

The third I replaced the knock sensor with a new one, still had the "43" come up, buddy took it into GM and they replaced the knock sensor and the ECM. This one was kinda weird, every thing looked fine on my scanner, until you shut off the engine and then it would give 2 or 3 knock counts.

There's a diag to test the knock sensor, but I don't have it handy...also IIRC, the diag also talks about faulty wiring to the ESC module. A few guys have used resistors (do a search for "bypassing the knck sensor") to see if the problem goes away, much cheaper than trying a new sensor, less messy too

Thing is though, on all three occaisions that I worked on the code 43, there really was no performance loss/drivability problems associated with it.

IIRC, one the SE light would light just a short while after startup, the othe two the SE light would light up during cruise.

><><><><><><><><><><

Also, the more I think about it, plug wires crosstalking can cause a false code 43, check the plug wire routing and make sure they're seperated well. Also make sure the knock sensor wire is not wrapped in next to the plug wires.

 

Thanks a lot Mike!
I will check out the knock sensor, because when I did my mods this fall, I thought the knock sensor seemed kinda "sloppy" physically. The connector was a little loose, so maybe there is something there!
I would never have guessed that the KS could be related to that code though?

Thanks again!

Ken