Lippy951

Hi Everyone,

I really need some help. I have been at this thing for weeks and looked through every forum possible and can not figure out what is going on. Everything I check or fix does not solve this running issue. Really need some fresh ideas and help from the guys who know these cars best.

Little back ground on the car. It is a 1986 944 Turbo. Really good shape and clean engine. I have had it since 2015 and I have completed some nice modifications to it. I have put at most roughly 1k miles on it since I owed it. Most recently back in 2016, I put Vitesse system on it. New turbo, PB, momonitor software etc. I got everything from Vitesse. John helped me tune it up and all has been well. I am getting ready to do some more work on it but I am holding off until this is solved.

Ok, here is what happened. The last time I took the car out and it ran very well. A friend of mine took his car out and we went out for a real sporty drive. All was good and put the car in the garage. About a month or so goes by and I went to start the car up and the battery was dead. I jumped the car and got it running. Pulled the car out to warm up before a quick ride. This is where it gets weird. I get in the car and give is some gas and it just wants to stall. Idles great, vacuum gage reads 16" to 17" like normal and the AFR are normal, dithering around 14.7. IF I shut the car off for a few seconds and restart it, everything is fine. After a few minutes, if I give it gas, it wants to stall. No changes to the car have been made since that drive.

This is where is gets even more unusual. Sent John a quick email about the car and he told me to try and run the car with the PB out and short the plug. This will run on the base setting. When I do this, here is what happens. The car barely runs, vacuum readings are very low. Around 8" to 10". The AFR is very lean to the point it just doesn't even register. After a week of testing everything, I decided to change the FQS switch to 1 which is +5% fuel. The car idled better and AFR came down a bit. So, I went to switch 3 which is +10% fuel and the car is close to running as it was before. I got the AFR around 14.7, vacuum is around 15" and it idles a lot better but not like before. I have no idea why is needs more fuel. I haven't driven the car because of it wanting to run lean.

Here is what I have tested so far:

Emptied the gas and put fresh gas in.
New 3 bar FPR and damper
Fuel gauge at rail - Static pressure 43psi, running 38psi, vacuum line off 44psi. Leak down test passed. All seems good here.
Fuel strainer and filter were changed about 2 years ago.
Ignition wires, rotor and cap were all done earlier this year. I changed the plugs after the running issue started, no change
New injectors from Vitesse. This were put on after running issue started. We thought maybe this was it. No change
Injector harness is new for Lindsey Racing. Install around 2016
MAF voltage is around 0.6 from the Momonitor. It is also getting 12 volts of power.
TPS was test out of the car and at the plugs. All passed. Also shows good on the Momonitor.
Vacuum lines. I test this in 3 parts. I take the intercooler pipe off and pressurized it. All good. I block off the turbo outlet and pressurize it the intake. All good. Then I test the lines off the banjo bolt of the inter cooler. All good there as well.
All grounds were cleaned when I installed the new turbo.
DME temp sensor test good. I have a new one if I need to swap it out. The one in there was changed out when I install the new turbo.
The O2 sensor was install with the new turbo was installed.
ISV seems to be working fine.
Reference sensor are new and install shortly after I got the car. I had a Porsche guy install them and made sure they were spaced properly.
Took the battery out and had it tested and it passed. Its about 5 years old. Almost due for a new one but I don't think this causing my issue.
Check the wiring from my Vitesse install. All looks good and I am planning to check it again.
DME and KLR were send to ECU doctors in Jacksonville , FL. They told me the units were good. They were sent out back in 2015 just to make sure they were good. No change here.

After car warms up. I unplug the O2 sensor and the car goes little leaner. The AFR goes to 16. I thought it would go rich.
John think the PB might be bad. That's why I am try to get the car running with the short plug in. No idea why I am getting two different symptoms with the PB and short plug?

Any thoughts??

I would really appreciate insights or help.

Marc

Tom M'Guinn

I trust you have sent John logs from the MoMonitor, and that they don't show anything useful.

Are you adding fuel with the piggyback? Or is it just running leaner without the piggyback for no particular reason?

This "feels" like one of those situations where the cause might be one of the things you already checked off your list (since you checked off so many of the most likely culprits).

If you are a zillion percent sure there are no vacuum leaks, I'd check one more time.

ECU Doctors are great at fixing broken DME and KLRs, but it is very difficult to find quirky little faults on a box that is basically working but having odd issues. This isn't a knock on them, and I always recommend them, but I know of two situations where they gave a box a clean bill of health even when they were causing issues. One was a KLR on my own car. It worked "fine" but would cause a noticeable hesitation when you floored it. ECU Docs looked at it and said it was fine, but the problem followed the KLR when I swapped KLRs with another car. So, just to humor me, I'd try another DME and KLR if you can get your hands on known good ones.

If you haven't already, check the DME temp sensor and TPS signals all the way to the DME/KLR, to rule out a harness issue. Wouldn't hurt to check for blink codes.

I'd change the battery. 5 years is old for a battery in the modern era and it's been drained, etc. You say it's getting 12 volts of power. It should be about 13.8 when running -- do you have that?

Have you confirmed the timing belt is aligned and didn't slip?

Humboldtgrin

Lippy951

Tom - I sent John some logs and nothing too much stood out to him. Since the PB was disconnected, I used the FQS to add +10% fuel. I am in the process of trying to find another KLR and DME to swap. I thought about that today and I will humor you, so I am looking for some. I put a new plug on for the TPS. It was bad (real bad) and I thought that was the issue. I replaced it, checked it out at the plug and with the momonitor and all was good and I saw no change. I ran the car tonight. DME temp senor was reading 246 ohms at 192 temp. So that checked out. I checked battery out tonight and with the car off it read 13.48 and while running it read 13.60. Little lower than 13.80. I will replace that soon. Went through the harness yesterday and checked all the connections on the Vitesse setup and all looked good. I replaced the fuel injector harness couple years ago. TPS plug I just fixed. Next on the list is to do the ISV plug and DME temp sensor plug. I will have to check the timing belt. That didn't cross my mind. I will go over the vacuum lines again. A zillion is a lot. I haven't driving the car yet because of the lean issue. But with the extra fuel, I feel more comfortable and then I will plug in the blink code lights and see what comes up. I made them couple years ago.

Humboldtgrin - Beverly Hill Cop, great movie. I might have to watch that movie this weekend! Anyway, I was looking to find a new harness but none are out there. LR full harness is looks great but not sure I want to tackle that right now. Everything I tested for looks good. I suspected the KLR/DME might be bad, that is way I sent them to the ECU doctors after this issue started and a swap would be great if I can find someone.

I was talking to another guy on the phone today who is on these forums, owns and works on 944, plus he is familiar with Johns system. We talked for about 45mins going over different ideas. He was very perplexed to say the least. So here is why?

PB In - car runs great like normal no issues what so ever. After a few minutes, the system freezes. When I have the PB software pulled up on the laptop and I am monitoring rpms, voltage, etc. I see it just freeze. At that point, any gas given to the car, it just wants to die. No revving what so ever. It even says "Factory Unit - Stops after 3 minutes". I sent this John and he has never seen that before. I shut the car off and restart it, everything is fine until it freezes again.

PB Out and Short in - The car runs like crap. Runs lean, vacuum is in the toilet and it barely runs. It will rev up and it doesn't freeze up. I add +10% fuel it run better.

My questions are:
1. If it was a hardware issue like vacuum hose, wiring, TPS or DME Temp sensor, etc., wouldn't that show up whether the PB was in or out?
2. The PB is just for fine tuning making the chip/board better, why such a completely different set of symptoms?
3. If the KLR or DME was bad, again why such a huge difference whether the PB was in or not?
4. Could the PB be corrupted or something or could the chip/board be bad? Then again why such a totally different set of symptoms?

I have not idea about electronics like this. I am more of nuts and bolts type of guys. I am asking because I am really trying to understand this aspect of the car. I appreciate the feedback. Keep them coming because I need them.

Tom M'Guinn

When the PB is in, are you adding any fuel with it?

As to your questions:

1. I would think sure so...but see below
2. Great question, that's why I was asking if you are adding fuel with the PB?
3. I'd agree that points away from the DME/KLR (but you never know -- see below).
4. I'd say everything is possible, although if runs poorly without the PB, then it's kind of hard to blame the PB (unless it took something else out with it).

Assuming you are not adding fuel with the PB (a critical assumption that makes the rest moot if untrue), I'd want to take a hard look at the MAF signal going to pin 7 of the DME. When the PB is installed, what is the voltage on pin 7 of the DME when the car is idling nicely for the first 3 minute (i.e. the MAF voltage in the momonitor)? Then, when you take the PB out and put in the shorting plug, what is the MAF voltage at idle? I believe both the DME and the PB convert the MAF analog voltage to a digital signal using some type of hardware analog to digital converter (ADC) chip. The piggyback no doubt has much more advanced hardware than the obsolete 8-bit converter built into the DME. So, if something odd were going on with the signal from the MAF, it's possible that the piggyback and DME are processing the signal differently, such that the PB is able to "deal with it" for a short time and send the DME its own good signal before shutting down, while the DME is simply unable to convert it properly in the first place without the PB, due to the DME's antiquated design. But what could be wrong with the signal if the momonitor shows a seemingly normal voltage? I honestly don't know. Maybe the current is too low, or it's super spikey, or it only stays at the correct voltage when the motor is running well? Similarly, it could be the DME's ADC on pin 7 is faulty, such that the DME is able to process the PB's (cleaner) signal for a short time, but not the MAF's. If it were me, I'd be very inclined to create my own clean .6+/- volt signal (with trim pot for tuning) and send that to the DME directly to see if the motor idles cleanly and, if so, whether anything changes by sending your own .6 volt signal through the PB. If you want to try that and need help creating the signal, let me know. Just a random internet theory, but the test would add to your diagnostic data set for sure.

By the way, are you running the ignition pulse through the PB too, so that you can alter timing? If so, I suppose something similar could be happening there, but seems less likely given your symptoms. It's also possible you have multiple things going on...

fast951

Marc,

You we're adding lots of fuel with the PB, which I consider abnormal. This is why I asked you to remove the PB as you were masking the real problem. The car should idle and run fine without the PB.

without the PB the MAF signal at the DME is normal. So there is something causing the lean condition.

As far as the issue with the PB, it must be investigated. So you need to send it in. Hopeful the dead battery and jump starting did not cause any damage.

fast951

To add to Tom's suggestions, if the car has an aftermarket cam it can cause a lean idle at stock 850 RPM. Some cams require higher idle RPM.

Tom M'Guinn

I see, so disregard my whacky ADC theory. So it sounds like the car is running very lean for some reason (mixed up ISV and AOS hose maybe?), and the piggyback may be having issues. John's maps are dead on accurate for a typical 2.5 turbo motor, so if your car is running that lean, Vegas odds say it's getting unmetered air. Alternatively, some sensor or malfunction could be reducing the actual amount of fuel being delivered, which would show up if you looked at the injector duty cycle and fuel pressure and flow testing. I once saw a car (not a 951) that bottomed out on a speed bump (or something) and squished the fuel supply line running under the car. Pressure looked good, but it couldn't flow enough to run right.

Lippy951

Tom,
I am not adding fuel while the PB is plugged in. I only added fuel when the short plugs are in.
MAF voltage with the PB in at 840 rpm, I am reading 0.73.
MAF voltage with the PB out and shorting plugs at 840 rpm, I am reading 0.62
How do I read the voltage at pin 7 of the DME when the car is idling? I could do this test if you think it could help.
Ignition Pulse via PB, I have no idea.
I had a Porsche shop do the timing belt and water pump when I bought the car so hopefully that didn't change, but will check anyway.
Not sure about the duty cycle, but testing the fuel pressure with the car off is 44psi, while idling its at 38 psi and with the vacuum line off its at 43 psi. Pressure looks good when revving it.

Hi John,
you have a great memory. I do remember adding some when you turned it after I installed your system. How much, I don't know. Would it be helpful to see that? I can either look it or send your that file?
I know I mention when we tuned the car or shortly thereafter that I could not download the previous save file to the PB. I get a download failure message. I know you mentioned that this wasn't a big deal and I am just wondering if I downloaded one of the previous files, would that make any difference diagnosing this issue and the freezing up? I will send you out the PB.
I changed the map with the dip switches and saw no difference in how the car idled.
Aftermarket cam, no idea. Anyway to check this out?

Tom, I with ya on the vegas odds and John has been really good to me and very helpful. So, then let's go back to the unmetered air. When I do the vacuum test, I take the intercooler pipe off and I install a cap with a Schrader valve. Then pressurize the system to almost 20psi. It hold for a bit then slowly goes down. I could post a video if that helps. Then I take the banjo line from the intercooler pipe and the two lines to the wastegate and test them. All is good. The only questionable part is the turbo area. I block off the turbo outlet and pressurize the inlet. Not too much, maybe 5 psi or so be it doesn't hold at all. The AOS is capped off when I do this test. There is air leaking out of the turbo body via soapy water. Maybe I didn't tighten the bolt down enough? Could this be the cause of my lean condition? The other areas are the rubber couplings which I can look at more closely for holes or tears. I do know the car idles worse when I cap of the ISV at the intake manifold and at the intercooler pipe. I would think that this is telling its working. The AOS is connected to the turbo inlet pipe.

So if I am understanding this right, if I had a vacuum leaked or unmetered air coming in, if we just add more fuel, this would masked it? And the vacuum gauge wont show this, at least the vacuum leak?

Lippy951

John,

Just to clarify, when you are talking about adding lots of fuel with the PB, that's not what I did. I only add +10% fuel via the FQS with the short plugs in after you told me to try and get the car running with out the PB in. Adding the fuel was the only way to get the car to run and idle. I never messed with the PB since you and I tuned a couple years ago. When we did that, I am pretty sure we took some fuel out because it was running a little rich. I remember checking the grounds to make sure they were good. I am sure we also ran the car with the plugs in to make sure everything was running ok

Tom M'Guinn

If your MAF voltage is .73 with the PB installed, and .62 with the PB not installed, then you are adding fuel with your PB as John said. That just means your car is running lean, for some reason, and the extra fuel is helping it run. Spray starter fluid around all the potential leak points (including the turbo you say is leaking) and see if the idle changes... If so, you found the leak.

Lippy951

Tom - I didn't realize that was what the voltage was showing. I thought we pulled fuel, I was wrong. I tried the starter fluid as well as propane to see if there was any change in idle. Didn't notice any. Only thing I saw was the bubbles coming out of the turbo housing. However, I did find two interesting discoveries over the past couple of days. I am going to call this round of repairs "Jump-n-plug".

I took the intake off to see if I could tighten the bolts up a little on the turbo housing. I found that the intake gasket on #2 cylinder was not reversed therefore blocking part of the injector spray. I know this is not good but is it bad enough to cause my lean condition?

I already made a new plug for the TPS since it was bad last week. See the picture, it's bad. I fixed it. I was going to replace the plug for the DME Temp sensor and ISV when I have the intake off next. I figure I would check the speed/reference sensor plugs to the harness. When I purchased the car, the guy told me that sensor was bad. So I replaced both and never had an issue with the car starting. I was truly amazed at what I saw. I read up on these sensor and I don't think it would cause my lean condition. Read that bad sensors causes starting issues and other running issues. Not sure exactly running issues are. Do you have any ideas what the running issue might be? I bought a new plug harness for the these sensors and I am hoping I see big difference in how the cars runs. I just have no idea how the car even ran with plugs in this condition. Can anyone thing of any other plug I should replace??



Reference sensor plug

TPS plug

Lippy951

Gasket on backwards
Here is the picture of the gasket partial blocking the injector.

gruhsy

Check every last one for sure. I am willing to bet you will find more