It is definitely time to tape the gauge to the windshield and go for a ride with a few WOT passes. That really is the best method because you need to see what the fuel pressure is doing under a load at WOT. It does sound more like a fuel delivery issue than a FPR issue. The white exhaust manifolds (and if the plugs are bone white, too) would certainly indicate a lean condition. When was the last time you replaced the fuel filter? A build up of debris could cause these problems as well. I would replace it immediately if you haven't already done so.

 

It is definitely time to tape the gauge to the windshield and go for a ride with a few WOT passes. That really is the best method because you need to see what the fuel pressure is doing under a load at WOT. It does sound more like a fuel delivery issue than a FPR issue. The white exhaust manifolds (and if the plugs are bone white, too) would certainly indicate a lean condition. When was the last time you replaced the fuel filter? A build up of debris could cause these problems as well. I would replace it immediately if you haven't already done so.

 

Well I taped the gauge to the windshield and went for a drive but it didn't seem to prove anything. The needle seemed more steady, it was at 38 at idle and at WOT with the engine pinging away it jumped right to 48 and stayed there. I shifted at 4500 and it never dropped from 48. I drove around for about 15 minutes so that I could check and see if there was any difference with the engine warm but everything still seemed to check out okay. This is really driving me nuts. I guess I better get the cable made.

 

Based on the latest fuel pressure test, it looks like fuel delivery is in good shape (at least up to the injectors themselves). I am anxious to see exactly what is happening to the timing at WOT.

 

Well I finally got around to getting a cable made, going to test it out tomorrow. Hopefully it will reveal something. I don't have a lot of experience with TPI motor, I have only had this car and an 85 IROC before this one. Something that I have noticed that is different between the two cars is on the IROC if you touched the TPS without moving the throttle you would hear the injectors speed up and the engine would die. On this car you can play with the TPS all day and it does not effect the engine at all, but will set an error code. Dan if you get a chance will you try this on yours and see what results you get.

Ethan

 

With my car idling, if I loosen the TPS mounting screws and move the TPS back and forth, my idle definitely fluctuates.

I forget what type of resistor the TPS uses, but moving it around by hand will definitely cause changes in voltage, falsely signaling the ECM different throttle positions. The result would be a noticeable fluctuation in idle and/or the engine stalling out (like you experienced on the IROC).

What code was set after you moved the TPS around? You had mentioned a while back that you checked the TPS and it checked out ok. How did you check it? Did you measure the voltage throughout the entire range of the throttle, from idle to WOT? Did it rise evenly from .54 volts at idle to about 4.5 volts at WOT? Based on what you described below, I'm back to thinking it is the TPS.

 

I checked the TPS out using an analog voltmeter, the needle appeared to move smoothly with no problems. I'm on my out to the garage now to test the cable so I will check the tps voltage with the program if everything works out good.

 

Good deal - hopefully the scan will provide some insight...

 

Well everything worked and I went for a spin around the block, but I'm not sure what to make of the results. One thing I did find is that the TPS voltage does not go above 4.04, this is with the pedel to the floor. I also noticed that as I drove at a steay speed the O2 voltage would jump back and forth around .5 volts like it is supposed to but if I even hardly touched the pedel it would drop right to 0 and if I stayed on it, it would ping and stay at 0 until I lifted then it would jump to .9. I'm not sure what I'm looking for in the BLM and INT but they were for the most part around 128 but ranged from 108 to 146, but those extremes did not have a lot of data points to average. Can you suggest anything I should be looking for?

 

Congratulations on successfully building the cable and getting everything to work

I don't think the TPS voltage at 4.04 WOT is an issue. I'm not certain what to make of the O2 sensor voltage data you are seeing versus the throttle positions you are describing, though. Maybe someone else will chime in with what should typically be seen.

Was the car in open or closed loop while you were cruising steadily? When you pressed the gas to WOT, did it go into open loop?

Where was the timing at during cruise vs. WOT? Were there any knock counts?

 

The car was in closed loop while cruising and would switch to open loop. I used the winaldl program so it showed knock counts but not timing advance. There were a lot of knock counts at all rpm ranges. I'm not sure what to try next, I guess I can try and go for a little longer drive and collect more data. The O2 thing bothers me, since every book I have read seems to say it should go instantly to .9 never to 0.

 

A high number of knock counts is at least a place to start, although you already said you hear pinging at WOT - at least we know the ECM is hearing it, too. It partly explains the sluggish performance, as the ECM will retard timing because of the knock detected.

Normally, you'd only get 1 or 2 knock counts here and there, so there is clearly an issue.

I am definitely no expert on the exact causes of engine knock, but some research there might prove helpful. I'll see if I can come up with anything.

Edit - after thinking about this - a very lean mixture / hotter cylinder temps will cause pinging. I know you confirmed that fuel pressure was not dropping off, even at WOT, so fuel delivery should be good UP TO the injectors.

I wonder if the problem is with the injectors? It might be worth it to measure each injector's resistance. They should be close to 16 ohms.

Sorry to keep throwing different ideas at you.

 

I changed the injectors maybe 2 years ago thinking that they were causing a problem but there was no improvement. I really think there must be some thing going on with the fuel pressure. I think next weekend I will pull the FPR apart and take a look, maybe there is something wrong inside that isn't noticable on the guage. Have you had one apart before? I'm with you on the timing I think the timing retard is what is killing me, it feels like you are driving everywhere with the brakes on. There not, I have checked .

 

I have never had the FPR apart. Based on diagrams I have seen, it doesn't look too complicated - a spring, a diaphragm, some type of check ball or valve to open / close the return port - that about covers it.

I'm not sure what the a/f ratio measuring limits are of the narrow band O2 sensor, but the O2 voltage going to 0 also indicates lean (very lean).

There is a fuel issue in here somewhere!!

 

I'll chime in with some input.
The WOT TPS of 4.04V is not an issue at this time.
You are correct about the bouncing O2 voltage, that is normal.
Going to zero when you hit the gas is very bad, it should be the opposite, you should be seeing over .800 mv at WOT.
The BLM's ranging from 108 to 146 is also a bad thing. 108 is indicating rich, and that is as rich as the stock prom can read...so you are maxed at that point. 146 is quite lean, with 160 being the leanest reading it will indicate.
The first place I'd look is vacuum leaks, it really sounds like a bad leak somewhere.

 

I thought a possible vacuum leak also. I have checked and can't find one and the car doesn't seem to act like there is one. The idle is relatively smooth for a engine with 180000 miles on it and vacuum at idle last time I checked was 17. I'm going to try and go for a longer drive and so that I can get more accurate BLM and INT numbers. I appreciate all the help and suggestions please let me know of anything else you can think of that might help.

 

180k miles? You may be having fuel delivery problems in one or more cylinders, by way of plugged or partially plugged injectors. This would account for good pressure but running lean and it would account for the O2 going to 0 when throttle is applied.
Unfortunately there is no simple way to check for this. The way GM calls for uses a tester and pressure gauge. This is called an injector balance test. The tester clips to an injector and your battery. You charge the fuel system and look at the pressure. Then you hit the button on the tester and it fires the injector for a set amount of time. you then write down the pressure when it is done. You do this for each and every injector. The readings are not supposed to vary more than 5%. If they do, replace the entire set of injectors. Oh, and you need to start and run the engine after doing 2 injectors to keep from loading up all of the cylinders with gas.
Another way you could do it (harder and messy) would be to pull the injectors up, keeping them in the fuel rails and keep the lines connected to the rails. Get 8 large babyfood jars and put one over each injector to catch fuel. Have someone crank over the engine and you watch the spray pattern of each injector. If any are not a nice even cone..replace the set. To further verify the injectors, get a graduated container (cc's would be best) and pour the fuel from each babyfood jar into it one at a time and compare the amount of fuel each injector put out. If there is a gross difference in the fuel amounts, replace the injectors. (Note, disconnect the coldstart injector before cranking the engine over)

Before going to all of this trouble though, get an ohm meter and ohm out each injector. You are looking for them to be 15-17 ohms (a little more or less depending on temp) and they should all be within 0.4 ohms. again, if any fail this replace the set. The reason I keep saying replace the set is that if any have failed, the others are probably going to follow suit soon.

 

How about the possibility of a failing MAF sensor? I've seen them fail such that it'll under report the actual air flow but not so much as to set a code. Since this sensor is one of the most important ones for calulating fuel delivery, it's stands to reason. See if you can substitute a known good one and recheck.

 

With the scanning software he is running he'll be able to see what the MAF is reporting and should be able to determine if it is close to right. Also..at WOT the ECM is operating in open loop again and the MAF isn't playing a role anymore, and WOT where he seems to be having the most trouble. Also, I believe he mentioned that it was changed already.

 

Everything, except the BLM's appear normal. If the 02 is going to zero volts, it's going open loop meaning the exhaust temp isn't high enough to keep the sensor at 600 degrees (or the O2 is bad or something like coolant, oil, too much fuel is washing it out). I'd verify that the ECT and MAT signals are close to ambient on a cold engine. Compare the ECT temp to the gage readout as it warms up. Track BLM's by Cell (there are 16). You want to start with it at idle and then at steady state cruise - maybe 1800 to 2200 rpms.