Ok, a lot of you know I've been chasing a phantom problem on my black car since the old motor setup last summer. One good dyno pull, and after that the A/F was stuck on the really rich side (about 10.5) and I had a terrible low end stumble, even with a neutral no load rev, if I moved the throttle fast, it almost choked out. I've killed the car by doing this.

Fast forward to a new motor, with everything re-used but the cam and shortblock. I'm still having that same issue. On a cold start it's fine, but after about 45 seconds something loses it and the problem presents itself again.

I just replaced the last part I hadn't checked, the fuel pump, and gotten nowhere. At idle, both side LTerms and STerms dump to 108 and 1 on both sides once it hits closed loop. The cam is a custom Joe O setup, and what's happening to me is exactly opposite to what is being said in the first part of this thread. Yes, the cam has big duration lots of overlap. The car doesn't seem to be burning rich in reality as there's absolutely no black smoke coming from it that I could see, and the stink and fumes ability to make your eyes water are all indicative of a lean condition.

Parts that are either new or have been replaced: Shortblock, Fuel Pump (Racetronix), Fuel Filter, AFPR (Hypertech, set to 43 with vaccuum line off), SVO 30# Injectors (no leakers I could find), Opti (was throwing DTC 36, putting a new one in, car will run fine with this code via service manual), TPS, MAP, Mucho tuning (not the problem), Plugs, wires, O2's (I'm upgrading to the heated ones next week), Ignition box and Coil (Accel 300+, car runs MUCH worse without it), and everything else checks out.

Anyone have ANY ideas at all???

 

Think you got that backwards. Stink and fumes that burn the eyes are indicative of burning rich. BUT what do the plugs indicate? Are they black? What is your vacuum level? What is your compression or leakdown level? I haven't followed your problem since the beginning so for give me if I ask questions you may have informed everyone else earlier. What is your engine temperature monitor reading from the ECM? Could it be indicating that the engine is not warmed up when it actually has but the ECM is enriching the fuel cause it thinks its still cold? Sorry got too many questions to help you out but curious minds want to know.

 

That's what I was thinking, and the plugs are showing rich. They're pitch black, and have about <1 hour of run time. Compression and leakdown should be fine as the new shortblock only has about 20 miles on it. Vaccuum is about 12-13 In/Hg at a 1050 idle, and about 9-10 In/Hg at a 800 Idle. My ECT is showing just fine. Approximate ambient at cold start up, no holes or anything I could see.

Something I'm wondering: the first time the car was on the dyno last summer after the H/C package, it got one good pull in, but was going lean on the top end. Second run did the same thing and started detonating and was shut down early. Could the going lean have damaged my injectors somehow????? Those are the only things I can think of that could be a problematic part at this point, as everything else has checked out.

 

So what about the engine temp sensor?

 

You talking about the Engine Coolant Temp Sensor, the one in the water pump?? If you are, then it's fine. Approximate ambient at cold start, can't see any holes as the temp goes up.

 

Since you've been trying to find this problem for a year now, don't assume anything! Do the leakdown test!! As far as your vacuum level is concerned it is way low. Once you get below 17, you have a tough situation. Don't know much about your setup but you should start hunting for a vacuum leak. In speed density, the PCM uses the Low Res signal from the OPTI, the IAT and the MAP for fuel management. Let's focus on the MAP for a second. As I understand it, at WOT throttle, MAP is high and vacuum is low. Therefore, when MAP is high, the PCM enriches the fuel mixture. Is it possible that because the vacuum level is exceptionally low that your MAP readings are always high and the PCM is enriching the fuel mixture because of that? This is were Fred comes in. Not entirely sure if the Low Res signal will override what the MAP is showing or not. (not formiliar with the algorithm) However, if the MAP is too high(over 80Kpa) and the throttle position is closed, it will set the SES light for code 33. Maybe your TPS is slightly off and the PCM will not set 33. Use the scanner and see what the MAP readings are when the problem occurs. Your programmed enrichment tables will also have a lot to do with it as well but that's a starting point.

As far the engine temp is concerned, you watched the temperature rise as reported by the ECM right? Not the gage right? Cause the gage uses the sending unit in the drivers head not the sending unit for the ECM which you identified in the water pump.

You brought up a point about the injectors. Perhaps they are dumping too much fuel. Well several things regarding that are as follows: If that were the case it should run rich even when it's in open loop. If they are dumping too much fuel when they are on, chances are (but not necessarily) that they are staying open when they are off. This would mean 2 things. The fuel pressure would drop like a rock after the engine was shut off and starting it back up would take several cranks. In addition, have you ever checked the vac line to the fuel pressure regulator to see if it's wet?

Hope that helps. After you get some of the data above, let's get Fred to help with it. He knows everything

Dave

 

My vaccuum level is going to be low. I'm not running a small cam, and it's got the signature Joe Overton ramps on it too. I'm actually very pleased with the vaccuum I'm getting out of it right now. There's no leaks anywhere, I've checked.

This problem isn't a MAP issue either, as it was present with my old stock shortblock and Heads and 224/230 cam setup. That one was pulling 16 In/Hg of vaccuum and the exact same thing was going on.

It's not the injectors because fuel pressure holds for quite a while before starting to drop. The AFPR is brand new and good, no leaking there.

I'm watching the ECT as reported by the ECM using datamaster. Not the gauge, those things aren't accurate for crap.

My TPS is at about a .55.

Like I said before, I've checked everything, and can't come up with a solution. This is just one of those mysteries.

 

I think you're missing something. First if you're having a compression or leakdown issue, it rarely comes from the rings but usually from the valves or a gasket problem. Which as I understand it, the heads came from an engine that did the same thing as the new one. So your supposition of "Compression and leakdown should be fine as the new shortblock only has about 20 miles on it." is flawed. Second, you stated "Fast forward to a new motor, with everything re-used but the cam and shortblock." Obviously something you moved over is defective. I believe a trip back to basics is in order and maybe a focus on ignition or engine control components is in order. You should at this point start over with the approach that you never saw the car before.

 

I realize that part. If it was a vaccuum leak large enough to cause those kinds of problems though, the car wouldn't old a steady idle via the IAC like it does either. The heads were rebuilt while the shortblock was being done.

 

Here is something you might want to check.... I'm not sure if it will help you or not, but this is a wierd problem that I had on my LT-1 Corvette.

Right after I installed the Hooker shorty headers (looks exactly like the exhaust manifolds, only they were less expensive) and removing the catalytic converters, the car would start running really rich on one side to where the oxygen sensor would clog. I replaced the oxygen sensor and it would be fine for a week and then start running really rich again. I did this twice then started looking into why it was happening.

Blah Blah Blah....four weeks later, after alot of troubleshooting and scanning, I finally tracked the problem down:

On the driver side (the side that was fine) the O-sensor was right at the collector of the headers. On the passenger side (the problem side) the oxygen sensor was down the pipe about 12 inches after the collector. What was happening was since the cats were removed, the passenger O-sensor was not being kept hot enough (the cat used to be right beside it) to operate as well as the driver's side one, which was right at the collector rather than 12 inches down, and so the car would start running rich on the passenger side because the colder o-sensor was telling the PCM it was leaner than it was. This would cause a domino effect to wear the PCM would keep richening it up further and further until the O-sensor would finally get clogged.

I welded an o-sensor bung on the passenger side right behind the passenger side collector, and moved the o-sensor to the collector like on the drivers side, and the problem went away.

So if you're running long tubes, you might want to check to see that your o-sensors are running hot enough. Maybe going to heated ones is the ticket. I have long tubes on my '97 Camaro and the oxygen sensors work fine.

The other thing to try is to maybe retard your timing at idle a few degrees so the exhaust system runs a little hotter to help them heat up.

Good luck.

-Dave C. '97 Z28

 

I'm actually waiting on new heated O2's and the wiring harness to come in so I can do the conversion. I'm hoping that's going to be the fix, but I'm not going to hold my breath either.

I'm running ASM headers, and the old single wire O2's seemed to be handling everything ok, I'd just get a little bouncing in and out of open loop at idle.