Car bogs on low RPM acceleration, rev limits above 5k...

1528 Views 11 Replies 5 Participants Last post by ttmkiv, Oct 30, 2001

AZWildcat

Discussion Starter · Oct 29, 2001

As you know, I rarely post for help, so that should be a sign of how truely desparate this situation has become. I have been on the car with a volt meter/ o'scope for 30+ hours this week to no avail. Anyway..

The update...

Smoking fixed: combination of cam covers that were too loose and a bad PCV valve.

Lack of acceleration fixed: Vaccum/boost leak, hose on the top of the throttle body broke.

All codes fixed: New knock sensor fixed the code 55. The sync issue was far more involved. First I hooked my scope up to the crank position sensor pins at the ECU and the waveform appeared normal. The sensor ohm tested correctly, but to triple check, I pulled the sensor off and looked at the teeth.. all were in place and the wheel wasn't wobbling.

I then turned to the cam position sensors.. Testing them on the scope at the ECU showed a good wave form for #1 and a questionable form for #2. I then tested the signals at the sensor pins-- both were good. (Their resistance was also good) I then ran a continuity test from the cam position harnesses to their corresponding ECU pins. The negative wire from cam position #2 was open, so I ran a wire from the sensor to the ECU harness, tapping both ends.

The result? All codes are cleared, but the car still runs like shit. It cuts out anywhere below 2000, bogs when the gas is hit under 2000, and rev limits itself when on the gas/boost. What am I missing? The car is almost undriveable. Could this possibly be mechanical?? I can't imagine how, but I've gone through my entire list.

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pooshda

· #2 · Oct 29, 2001

Im not 100% sure if I had the same problem before or not, but I had it pretty bad before I replaced my turbos... although it was only for one drive and then mysteriously stopped..

Im sorry I cant help but I do have a question regarding smoking... when we put my turbos back together after replacing them, I seem to have a small amount of oil on my turbo heat shield and sometimes a rather SMALL amount on one of the turbo pipes under the black metal vaccum pipes... my friend thought maybe it was a result of a PCV valve.. which could be the result of the oil, in turn causing the smoke.. is that possible?... also someone once said something like the stock BOV can blow a little oil on the heat shield, but it never happened much before and not this much oil.. its not BAD, but its more than a few drops.. any idea? Im worried that it was maybe gasket related somewhere, and that would suck cuz putting it back together was a pain in the ass... very small work space

My Vac is also pulling in 25lbs on the boost guage, that seems a BIT HIGH... doesnt it?... car runs fantastic though, other than the little oil on the turbo piping/heatshield area =|

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ttmkiv

· #3 · Oct 29, 2001

It sounds like I am having the same issues as you. Have you tried going over the VPC wiring and sensors with a fine tooth comb? My car bogs terribly when i first step on the gas. The rpms will drop down to about 1k and then pick up again. I almost have to double pump the throttle to get the motor to rev up. I checked everything with the VPC and AFC connections, and turned nothing up. So i decided to quickly fab up a way to run the stock MAF again, and tested that. The car ran MUCH better, and that is where i stand right now. I still havent figured out what is up with the VPC.. So if you havent checked the VPC sensors, and wiring, check that. Let me know if you find anything, or get it running again, and I'll do the same.

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SyCK

· #4 · Oct 29, 2001

AZWildcat said:
[B

The result? All codes are cleared, but the car still runs like shit. It cuts out anywhere below 2000, bogs when the gas is hit under 2000, and rev limits itself when on the gas/boost. What am I missing? The car is almost undriveable. Could this possibly be mechanical?? I can't imagine how, but I've gone through my entire list. [/B]

May not be relevant but my car acted alot like that awhile back.. ran like ass and rev limited at around 5K. After replacing the cam sensor and crank position sensor it just ended up being the cam gear slipped and sent the cams' position all off. Time, money and labor wasted cause I didn't simply check that first. Worth a shot if you haven't looked there yet. *shrug* dunno....

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pooshda

· #5 · Oct 29, 2001

If I rev my car in park... I cant go much higher than 5k before it seems to stop.. and my exhuast makes a very loud pop... that all happened after the DP/exhuast, it would rev all the way to redline before.. although, it shifts at redline while im actually moving.. so I guess thats normal?... or not?

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AZWildcat

Discussion Starter · #6 · Oct 29, 2001

Aaron,

The "double pump the throttle" is the most interesting part as that's exactly what I have to do. Do you have any problem running the car out however? What were you doing before the car went into this problem? I was running at the drag strip.

If there's anything I know about cars, it's electrical and that's why this problem irritates me so much.. I can't figure it out.

ttmkiv said:
It sounds like I am having the same issues as you. Have you tried going over the VPC wiring and sensors with a fine tooth comb? My car bogs terribly when i first step on the gas. The rpms will drop down to about 1k and then pick up again. I almost have to double pump the throttle to get the motor to rev up. I checked everything with the VPC and AFC connections, and turned nothing up. So i decided to quickly fab up a way to run the stock MAF again, and tested that. The car ran MUCH better, and that is where i stand right now. I still havent figured out what is up with the VPC.. So if you havent checked the VPC sensors, and wiring, check that. Let me know if you find anything, or get it running again, and I'll do the same.

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AZWildcat

Discussion Starter · #7 · Oct 29, 2001

Re: Re: Car bogs on low RPM acceleration, rev limits above 5k...

Euphoric said:
May not be relevant but my car acted alot like that awhile back.. ran like ass and rev limited at around 5K. After replacing the cam sensor and crank position sensor it just ended up being the cam gear slipped and sent the cams' position all off. Time, money and labor wasted cause I didn't simply check that first. Worth a shot if you haven't looked there yet. *shrug* dunno....

Actually, that was one of the first things I looked at. The cam timing *appears* to be good, but the problem is I can't see the crank's timing. So, they both may be off relative to the crank. I am considering a timing belt change just for good measure.

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ttmkiv

· #8 · Oct 29, 2001

Dennis-
I didnt run the car out all the way, when that problem was happening. It would sputter and bog and then rev up fine, but i never took it into heavy boost or much past 5k rpms, as i wasnt sure what was wrong with the car at that point.

My car started doing this after i reinstalled the head after having the valve stem seals replaced...

Do you have the tool to test the VPC pressure sensor with? I forget what it is called, but its something that you can apply a specific pressure/vacuum to the sensor and get a reading on its output. I'd be interested in hearing what you get for values. I can never get close to what the values are supposed to be for the pressure sensor even at atmospheric pressure. Its supposed to read 1.744 volts between the blue and yellow?? wire with the car in the accessory position and the hose off of the pressure sensor. I usually get somewhere around .5V and it drops off to 0.

AZWildcat said:
Aaron,

The "double pump the throttle" is the most interesting part as that's exactly what I have to do. Do you have any problem running the car out however? What were you doing before the car went into this problem? I was running at the drag strip.

If there's anything I know about cars, it's electrical and that's why this problem irritates me so much.. I can't figure it out.

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Grant

· #9 · Oct 29, 2001

Dennis, if the crank pully slips a tooth the whole car will shake and it will idle like shit (at least with the exhaust cam already set to -3). It will drive just fine other than that and the obvious lack of power. Also the check engine light will flash (sometimes) on my 97.

This may seem like a stupid suggestion, but if you have a geforce, have you tried another ECU? From the sound of it something bad happned to the electronics in the car, maybe something in the ECU got fried?

I don't really see how a bad airflow signal could cause this, but you could find someone with an OBD2 scanner you can log long term fuel trim. If its doing all sorts of weird things, you know the airflow signal is messed up. Or just put in the stock MAF.

First thing I would do is suspect aftermarket parts.

Also, the car will rev limit at 5k normally if its in neutral (or if the clutch is in, I _think_). There was a thread about this on the list where someone had their clutch sensor switch (or whatever its called) go bad and the car would always rev limit at 5k. Doesn't explain the bogging however.

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· #10 · Oct 29, 2001

Check the VPC pressure sensor lines to make certain they are tight and connected properly (no tears or leaks either). Also, check the VPC temp sensor. They are very easy to break. Definitely sounds VPC releated. See if you can rig the MAF back up temporarily as Aaron suggested.

Check the manifold pressure lines to the FPR etc... Any manifold presssure leak will cause the VPC to act funny.

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AZWildcat

Discussion Starter · #11 · Oct 30, 2001

I am very happy to say that significant progress has been made...

Today I took the car over to Billy's to check the timing and really to get a
second opinion. He looked at the timing and decided the car had not jumped a tooth, so we started looking at other things...

I knew the #2 cam position sensor was a little suspect, but I thought it was
working ok after the new wiring. (I 'scoped it at the ECU and it's waveform
looked like cam angle #1) Billy suggested pulling the sensor and starting
the car... I had thought of that, but didn't think the car would start. To
my shock, it did start AND ran well! No more bogging/missing/etc. It is
still rev limiting, but I think that's to be expected. Anyway, it APPEARS as
though this problem is on the downward slide. Thanks Billy!

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ttmkiv

· #12 · Oct 30, 2001

Dennis-
What did you do with the cam sensor? Just unplug it and start the car? Keep me posted with your progress if this fixes your car.. Thanks!

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