Lean Misfires at 2700-2800 rpm

[Roybatty]

Prowler - I can see you don't sleep!
A quick update - I was finally able to resolve my 2 to 3k stutter - I ran through the entire TB valve plate O-Ring fix/TB cleaning - and as a bonus shes actually idling correctly also. I did also do the following - TPS check per manual, ISC cleaning, BOV adjusting, ensuring battery hook up is good (I have a neg battery cable that tends to loosen) and even added some plumbers tape to some choice areas (screw in BOV etc - screws that don't get too hot in intake). You have got to love this Forum - thanks all.

[ProwlerGT]

Originally Posted by Roybatty

Prowler - I can see you don't sleep!
A quick update - I was finally able to resolve my 2 to 3k stutter - I ran through the entire TB valve plate O-Ring fix/TB cleaning - and as a bonus shes actually idling correctly also. I did also do the following - TPS check per manual, ISC cleaning, BOV adjusting, ensuring battery hook up is good (I have a neg battery cable that tends to loosen) and even added some plumbers tape to some choice areas (screw in BOV etc - screws that don't get too hot in intake). You have got to love this Forum - thanks all.

I can't believe I posted like 4or5 hours ago on here. WOW....... yeah nice to see someone notices I don't sleep... always taking one for the team. LOL - The TB o-rings are a great fix that I didn't even know about till pretty recently, but I think Dex has tried that (rebuilt his TB or got new) and its still an issue. GREAT to hear you resolved it though!

[DoctorDex]

Modlist is in my vB garage.

1. I don't have a barometric/intake air sensor because I use a GM MAF that feeds fixed baro and temp signals to the ECU. I haven't checked my engine coolant temp. per say, but it does put off values that seem to be correct.

Not sure how you want me to test my grounds. Please explain.

2. It still misses when the car is warm, its just not as noticeable. When the car is cold, the miss causes a large lurch, whereas when it is warm its just a little lurch.

3. I don't have a VIC motor (manuals don't have these). I've replaced my ISC with a brand new one --> no effect.

4. I've run the engine with the turbos disconnected and the problem was still present. I'm going to try this test again, just to be thorough.

5. Will try the exhaust thing sometime, but I doubt it will fix the problem.

6. I'll check the alternator voltage.

[ProwlerGT]

Originally Posted by DoctorDex

Modlist is in my vB garage.

1. I don't have a barometric/intake air sensor because I use a GM MAF that feeds fixed baro and temp signals to the ECU. I haven't checked my engine coolant temp. per say, but it does put off values that seem to be correct.

Not sure how you want me to test my grounds. Please explain.

2. It still misses when the car is warm, its just not as noticeable. When the car is cold, the miss causes a large lurch, whereas when it is warm its just a little lurch.

3. I don't have a VIC motor (manuals don't have these). I've replaced my ISC with a brand new one --> no effect.

4. I've run the engine with the turbos disconnected and the problem was still present. I'm going to try this test again, just to be thorough.

5. Will try the exhaust thing sometime, but I doubt it will fix the problem.

6. I'll check the alternator voltage.

1. Grounds - I imagine if you follow a few of the tests for ground continuity in the manual for testing sensor grounds in various locations in the engine bay and at the ECU that this will either tell you that you have a good grounded setup or not. In tracking down shorts all over my engine bay the more wires I repaired the better my ground continuity or OHM level rather became. I'm not an electrician, but I know I did it right at the time. Just see what the values or results should be for checking grounds at various sensors. Can't hurt.

2. Guess its running REALLY rich when its cold aye?... like more rich than usual?

3. Damn I thought I saw this in the service manual for turbo's and NA's.

4. COOL.

5. Yeah, I dunno... I just pulled that one out of my ass. Perhaps the SOUND it makes when the exhaust is off will lead you to some clue..... who knows... or what would be awesome is if the miss went away and then you'd know you have a restriction..... but restriction doesn't make sense cause it would seem like it would be ALL the time.

6. Cool deal. After I suggested that I actually read in one of those other car threads that someone recommended checking that as well.

7. I don't know much about engine internals as I've never had the opportunity to break one down and build it back up, but someone tell me if our engines have all that stuff (LOL) I mentioned with the valves n what not. I know we have valves n stuff, but just don't know if some of what I suggested is relevant to our platform with regards to what I said 4 posts back.

8. See if you can work out a deal with IPO or AEM or someone who will let you borrow an AEM ECU and see what happens then. Show them this thread.... that should be incentive enough as it will help them with sales and image in the long run (not that they really need help, but more lend of the hand is better always). Tell ya the truth man this would be my first priority over everything else discussed...... get any other ECU brand in there other than the Mitsu stocker and see what happens.

[DoctorDex]

I'm definitely considering an AEM. However, I'd hate to buy one and then have it still miss. Plus, I understand its a bitch to tune and you need a laptop for tuning. I don't have a laptop (although I suppose I could buy an old one) and I hate the idea of having to tune with a laptop... just not convenient.

As far as this air flow issue causing the miss, I don't think the two things are related. I did some more driving around and while driving in 1st and 2nd gears and the AF signal shows a smooth transition even though it misses. It seems that the aberrations in air flow signal only seem to come on in 3rd, 4th and 5th gears. I think this may be the "pressure pulsing at part throttle" problem talked about here: Pressure Pulsing at Part Throttle, Measurements and a Solution

[DoctorDex]

I'm interested in the valve idea. Like I mentioned before, I have a loud ticking from my rear valve cover. Its not an exhaust leak, its not rod knock and I have big bore lifters, so it shouldn't be them. My compression checks out, are there any other tests I could do? Leak down?

[DoctorDex]

Drove the car with the turbos disconnected this afternoon. Damn she's gutless without the turbos.... Anyways, with regards to the problems, the car still misses, but the pressure pulsing I was getting in 3rd, 4th and 5th gear is gone.

With that being said, its not like I'm going to drive around without the turbos connected just to get a rid of the pressure pulsing. I think I'm going to have to look into switching to a MAP system, that way I can hook up my SSQV to act like a bypass valve (kinda like the stock BOV with the hole in it). I tried doing this with the blow through setup but it seemed to make too much turbulence in front of the MAF with the BOV open at cruise. I might try taking a grinder to my Y-pipe first to see if I can smooth out all of the rough parts that could be adding to the turbulence.

As far as sorting out the missing goes, I think the next step for me is to try and get a hold of an oscilloscope (my neighbor was going to see if he could find one) and then hopefully try my ECU in a friends VR4 (he is very reluctant).

[brattesani]

why doesnt he want to let you try your ecu in his car? its not gonna screw anything up...

Originally Posted by DoctorDex

Drove the car with the turbos disconnected this afternoon. Damn she's gutless without the turbos.... Anyways, with regards to the problems, the car still misses, but the pressure pulsing I was getting in 3rd, 4th and 5th gear is gone.

With that being said, its not like I'm going to drive around without the turbos connected just to get a rid of the pressure pulsing. I think I'm going to have to look into switching to a MAP system, that way I can hook up my SSQV to act like a bypass valve (kinda like the stock BOV with the hole in it). I tried doing this with the blow through setup but it seemed to make too much turbulence in front of the MAF with the BOV open at cruise. I might try taking a grinder to my Y-pipe first to see if I can smooth out all of the rough parts that could be adding to the turbulence.

As far as sorting out the missing goes, I think the next step for me is to try and get a hold of an oscilloscope (my neighbor was going to see if he could find one) and then hopefully try my ECU in a friends VR4 (he is very reluctant).

[ProwlerGT]

Originally Posted by brattesani

why doesnt he want to let you try your ecu in his car? its not gonna screw anything up...

A bad ECU can kill the IAC for 1.... and who knows do what else. If your friend is so reluctant..... you can maybe sell the idea that you will test your IAC first and try it in your car.... 9 times out of 10 the IAC is what fries the ECU and vice versa..... at least that seems to be the going knowledge on the boards here.

I think verifying the wave forms is a great idea - oscilloscope - there are some cheap oscilloscopes on ebay (software kind) that you could plug into the laptop.... though you'd need a long lead/probe.

Yeah.... I'd check the valves... take apart engine day. Sucks, but what else is there after the oscilloscope???

I was thinking earlier tonight..... what about something uncommon/odd like the Vehicle Speed Sensor? Isn't that attached to the tranny through the speedo gauge?

[DoctorDex]

I think oscilloscope is the next step (if I can't convince my friend).

Its late and I'm tired and I've had a stupid idea that maybe the pressure pulsing and missing are somehow related?

Here's why: If you have a cylinder that doesn't fire and there is no fuel dumped into the exhaust then the this would cause the turbo to temporarily slow down. Could this be causing the pulsing?