RPM dancing, poor driveability, help!

I have a 1991 3000gt vr4, 117k miles, bought it with a lower end rebuild 500 miles before i bought it.

drove car home after driving, it. eventually got a logger installed, noticed that my rpm seems to go up and down, in idle, during cruise, even in wide open throttle the rpm will drop sometimes before going up. this feels more like a loss of power, than a bucking motion.

It has a slight misfire at idle.

I had found a front o2 sensor harness smashed, but i think i may of mixed up a couple of the wires when i put a new plug on it. front 02 sensor was reading .2v even when full warmed up, and not fluctuating. fixed the 02 sensor wiring, still getting hte same reading, i may of sent 12V heater power, to the sensor ground circuit, never smelled anything smoking but may be damage somwhere, rpm fluctuation existed before i messed witht he o2 sensor and still exists though.

The o2 sensor wouldn't effect warmup or wide open throttle, so i don't think it's the culprit to my rpm fluctuation(rpm goes up and down like 10 times a second constantly)

during warmup, my o2 sensors read lean, then work towards rich, the wiki says they should start rich, and work towards lean before fluctuating back and forth once warmed up. My rear o2 will start fluctuating, but my front o2 just holds a steady voltage.

with car in run, without the engine running, my 02 sensors both read 0.03-0.05v.

I also checked my plug wires, they are bosch, all have continuity, though the resistance is much lower than stock, could these be a problem, the wires themselves are in good condition.but only 600 ohms per foot, instead of like 4500+ ohms per foot of stock wires.

I've got ngk coppers heat range 7 gapped to .028, car has 19t turbos on it, running on wastegate pressure of 11psi.

I'm just not sure where to chase this problem from, don't wanna just start smacking it with the purse, i'll end up parting it if i can't figure out how to fix it. any help appreciated!

I can attach a warmup log if you'd like. actually file size limit is 100kb so i can upload it somewherehttps://datazap.me/u/kruqnut/more-cr...p?log=2&data=8

Oh, also about the car, has vacuum delete, no EGR or Purge at the moment.

I guess what I'm asking, if you were a proper service shop that knew about 6g72tt engines, what would be the troubleshooting procedure to figure out what is wrong with the car?

I have checked plugs, put new copper NGK heat range 7 plugs in, gapped at .036, .032, and .028.
I have checked the spark plug wires for cracks, checked the resistance.
I have checked the harness on the CAS, and on the MAF. I have tried swapping mafs.
I tested the PTU and also tried swapping one.
I pulled apart the ECU and checked caps, they were good, I replaced with a chrome ecu anyways.
I disconnected the ECS computer.
I replaced the injectors, with 560cc evo injectors, set the values and latency in chrome, and flashed it.
I replaced the injector connectors.
I did compression check on cold engine, 135 even on all 6 cylinders with a cheap harbor freight gauge.
I replaced the intake, lower intake, throttle body gasket, and biss screw 0 ring.
I sprayed starter fluid heavily on every connection while car was running and had no change in rpm besides the fluctuations.
I put pressure into the intake system and it holds some pressure, though not much, extra pressure seems it is leaking thru the valve cover, as i noticed the cap bobbing up and down when i had it slightly loosened. I haven't isolated the intake anywhere to try to avoid sending air into the engine in order to pressure test the piping and turbos etc outside the relief from the crankcase.
I checked timing, adjusted CAS to 5 degrees.

After this log I re-set the idle, the best I could with a fluctuating rpm.

bump for help!

daily bump for help

You're bumping a post that is already sitting at the top. Stop. No one is around on the weekend. People will answer when they see it.

i haven't backed out of the forum, i just have the page loaded, is it hurting anyone? i waited almost 24 hours to bump it

The point on a BUMP is to BUMP it to the top of the page. When it is already sitting at the top of the page it is a wasted post. It will stay highlighted as a new post until it is viewed.

Well, what I see in that log is your front O2 is dead and your timing is jumping everywhere.

Step 1 is to fix a misfire if you have one, you can't move on to anything else until the car will idle correctly. I don't know what a "slight misfire" is, you either have it or not. You'd have better luck unplugging both O2 sensors during your diagnosis and running it in open loop.

Also, 135psi seems low to me, I'm used to seeing 155 psi.

Yes I know the front o2 is bad, i had this problem when it was still working but on a smashed connector. Also the log is open loop, as the engine is still cold in it. The rpm fluctuating exists in open and closed loop.

It misfires lightly every 10-15 seconds once or twice. the RPM fluctuates much faster than the timing changes in the log, but maybe i can get a more precise timing value to log? I would guess its misfiring because the engine is stumbling so much and it can't compensate for the rapid rpm fluctuation.

I tested the compression cold, on a cheap gauge, it was exactly the same on all cylinders, i don't know what would cause an even compression loss on all cylinders evenly, I took the consistent reading as solid, the manual said 115psi was the minimum for a TT engine.

besides the o2 sensor, if i'm having problems in open loop, what do i check?

A misfire is a very open ended problem. Plugs, wires, coil pack, ECU, PTU, any of the wiring inbetween, fuel injectors, fuel pressure regulator, etc. etc. etc. It could be ANY or ALL of those. It's too open ended.

The people on here are VERY knowledgeable about these cars and would definitely be able to help, but you have to rule out some of these things on your own. If you can get it to not misfire on idle or free-revving the engine, then we can start figuring out issues. Until then, you'll have to put your mechanic hat on and learn/figure out what the potential issues could be and start ruling them out.

I have done many tests and been mechanicing, im running out of tests, that is why i am asking for help. You maybe missed the long list of things i ruled out? Which contains many things you listed, as well as the misfire being not very frequent and only in idle, while my problem exists constantly 10-20 times a second, in all modes of operation?

I'm not chasing a misfire, I'm chasing my engine running improperly, all tests on ignition system, ecu, plugs, wires, coils, ptu, fuel injectors, have been mentioned above.

Fuel system may be an issue, as our 3s has no easy way to just slap a gauge on it, i haven't tackled that yet.

Make sure you're getting a good signal to the fuel pump, and if you have a stock FPR they will generally overrun but I haven't heard of one under running on fuel pressure

Do you not have a wideband gauge? 19t's, 560cc injectors... I see nothing about a wideband though. Kinda like step 1 when tuning a car. 560's are known to idle poorly too.

i've got a chrome ecu flashed for the 560cc injectors, not supposed to have any problems, as the latencies are programmed in for the 560cc. The problem existed before i put the new injectors in as well, on the stock injectors, new injectors were installed partially to attempt to fix this issue, the turbos will need them when tuned. This problem is existing in all conditions, i don't have a problem with an idle, i have a problem with my rpms fluctuating, this shouldnt be treated like an idle problem. This is an overall engine problem at this point.

I don't have a wideband gauge. Have one, not installed yet until i get a new downpipe.

stock fuel pump, with a new oem regulator. I may install a fuel rail setup that allows or has a pressure gauge on it. if I don't part the car out.

There is afr information in the logs, not direct, i can see the rear o2 is lean. front o2 is dead so i will have to replace that, tho when it was working i was having the same problem. I broke that replaceing the crushed connector on it.

You respond to my attempts at leading you in a direction with "I know I have those issues, but that's not the issue I'm worried about". I'm not trying to be an ass, but you've gotta get this stuff square.

Your RPM signal comes directly from your PTU. Look at the wiring diagrams (they are free for download on 3sx). If your issue really is "an overall engine problem" then there's no amount of internet troubleshooting that is going to help you.

I'm aware of the source of the rpm signal, the question is, what is causing the rpm to move up and down, I've tried swapping ptu's already and got the exact same results.

Me saying I know the o2 is bad, but it's not the problem, really shouldn't be an issue here, i'm describing an issue in open loop, where o2 sensors don't matter.

if its an overall engine problem, there still are ways to diagnose what the engine problem specifically is.

I spent alot of time going over the service manual, and testing the procedures outlined in it, for all the parts i described, ptu, maf, cas, coils, wires, plugs, injectors, timing, idle, etc. And im still having the same problem, and found no problems using the factory suggested troubleshooting.

I spent time outlining everything i've done and my conclusions, in hopes people wouldn't tell me to do obvious things over and over again.

and no i don't have a wideband, i haven't started tuning the car yet, it's still on a base tune besides the injectors being updated to be 560cc and their corresponding latencies. wideband is planned, but im not going to dump $1000 dollars on the car smacking it with my purse, if theres serious engine problems of some sort, i'll part it out if i can't find help.

fuel pressure overrun would cause richness wouldn't it?

560s have known issues. IIRC they are actually closer to 590. There are threads here regarding such.

EDIT: Thread here shows there are two different latency values https://www.3sgto.org/threads/7965-E...ighlight=560cc

Quote:

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Originally Posted by kruqnut

Me saying I know the o2 is bad, but it's not the problem, really shouldn't be an issue here, i'm describing an issue in open loop, where o2 sensors don't matter.

if its an overall engine problem, there still are ways to diagnose what the engine problem specifically is.

I spent alot of time going over the service manual, and testing the procedures outlined in it, for all the parts i described, ptu, maf, cas, coils, wires, plugs, injectors, timing, idle, etc. And im still having the same problem, and found no problems using the factory suggested troubleshooting.

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You say things like this that give me a glimmer of hope that you know what you're doing. But you don't seem to get the principle issue behind what you're saying. There are known problems but you want to overlook them. The issue is probably a small cheap one to fix, but you seem intent on us leading you to the source at this point. As I've said, you've given us an incredibly open ended issue.

Quote:

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Originally Posted by kruqnut

and no i don't have a wideband

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Widebands can tell you what your engine is doing, more than your narrowband o2's will which is why it's step 1.... aka not throwing on turbo's and injectors and a tune first.

Quote:

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Originally Posted by kruqnut

i haven't started tuning the car yet

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Yes, you have. Don't know why you think otherwise. What do you think a tune is?

Quote:

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Originally Posted by kruqnut

it's still on a base *map* (corrected) besides the injectors being updated to be 560cc and their corresponding latencies. wideband is planned, but im not going to dump $1000 dollars on the car smacking it with my purse, if theres serious engine problems of some sort, i'll part it out if i can't find help.

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You may as well give up then if that's your attitude. You're expecting the internet to blindly guide you to a solution. I have no idea if the engine is assembled even remotely well, much less if you know what you're doing.

You've got some kind of airflow issue *I think*. I'd ask what your wideband is doing during idle and when you give it gas, but that's obviously not an important part of this to you, so I can't assist any further. Good luck.

And like I said, 560's have known issues. But what the heck do I know, I'm some random dude on the internet.

i didn't throw turbos and injectors and a tune at it. car came with turbos and no tune when i bought it, i thru the injectors in to replace the old ones, and knew i would need an upgrade when i tuned. Wideband is already purchased, but i need a new downpipe to go with it.

I don't know how well the engine is built, i didn't build it, you want me to tear it down for you, then rebuild it so i can verify the quality of the build?

I'm asking what i need to test to fix a dancing rpm issue, and you want to continually focus on problems with the car, unrelated to this issue.

I'm not asking for a solution, I'm asking what do i need to test to find my problem.

I've read up on the 560cc's and have done my research. But you know, since i have already told you, this same issue existed on the stock injectors, and nothing changed when i put the 560cc injectors in. But you keep trying to focus on that. I'm not stupid about this shit, I've already read pages upon pages of these forums looking for help before I made this post.

i'm sick of being on the defensive here, but 3/4 of everything you post is just telling me to either do something i've already done, or telling me about some issue that isn't directly related to my issue.

I don't have the wideband installed, what can be done without the wideband? The cars come stock without wideband, so how would i diagnose the problem in that situation?

When the snow melts again I'm going to run another compression test on the front bank since that seems to be where my o2 sensor is reading flat, and my pulse widths on injectors are longer etc, so seems to be lean there

maybe i messed up the front part of the engine the one time i ran the car after i swapped the o2 connectors and had to limp it home. but it's still behaving in idle etc just like it did before all that happened.

my 560cc were flow tested right around 560cc all of them within 1%. the car idles and runs down the road, exactly the same with the 560cc as it did with the stock injectors.

So if nothing changed when i changed injectors, you still think its the damn injectors, and keep telling me that my injectors are the problem.

If it's an air issue, what do i test, I've been over the MAF already, and been thru the system umpteen times for leaks and have found none, i had a couple on my throttle body and i fixed them, but car is still running the same. all details in the log are showing that the computer is trying to compensate for a lean condition. as far as I can read them. the rear o2 when warmed and fluctuating is staying below .5, the front o2 is at .2 and barely moves much at all. Maf readings were the same on both MAF i have.

I understand front o2 being bad will cause issues with AFR in closed loop. if my problem was only closed loop, i would fix this before i tried to do anything else, but since my problem is open loop as well, i'd like to find the problem before i go investing hundreds of dollars more into this car.

Change the periphery in chrome to run in only open loop and take your bad o2 out of the equation. Open loop and closed loop aren't something the car just does at idle. Open loop occurs at ~3000 rpm and closed loop/o2 feedback below 3000. If you haven't changed the periphery, I would do that and see if it works any better.

I can try that, thanks, i know open loop and closed aren't an idle thing, car is open loop till it warms up, then runs closed loop at low power situations.

-everything on hold right now with the winter storm we got.