Overboost fuel cutoff?

chally72 · 04-03-2010, 12:50 PM

Hi, I am having a problem with my newly purchased 86 944 turbo. I am getting a HARD fuel cutoff at approx 1.2-1.4 bars of boost (according to the stock gage in-dash). I read the recent thread on this forum about boost issues and was a bit confused about the answers, so excuse me as I ask again.

Here's where it gets a bit more muddled: The car does not have the stock turbo, (don't know what it is,) and it also has an older HKS Electronic wastegate valve controller. The HKS unit has power and the wires disappear under the dash, but it seems to have no effect on the boost limit and the previous owner was clueless and never even used it.

I've checked the pressure lines going to the dash gage and also to the (KLM?) computer in the passenger footwell, and there are no leaks, but I really don't know where to go from here. I've owned a NA 944 for several years, but this is the first turbo car of any make that I've owned or driven.

Thanks!

phil944 · phil944's Garage

Mine does the same thing. Under acceleration, especially in 4th gear, it'll just cut out. I looked around a found my cycling valve (thingy under the intake manifold with three vac lines and one electrical connector) had one of the nipples sheared off. I bought a new/used one and i hope that fixes the problem. I'll let you know when i get chance to fix it.

You shoud check to see if your cycling valve is intact.

Phil

chally72 · 04-03-2010, 03:13 PM

Oh boy, here we go..... 3 years owning an 84 944 with NO problems, and I'm getting the runaround today!

Car will not start now. No spark coming from the coil. I have 12v to both sides of coil and the DME relay is ok. The tach does not "bounce," though. Following the advice on this forum, I checked resistance on the speed and reference sensors with a multimeter and they are within spec. Wiggled wires and prayed to the gods to no avail.

In my limited driving experience with the car, it would skip slightly when backing off the throttle above 2000 RPM. Sound like a sensor? Other ideas?

And phil, thanks for posting. I will check that when I get it running again. Once again, I've read through some helpful posts on this forum about that valve.

chally72 · 04-03-2010, 03:34 PM

Well, no start situation solved....my own stupidity. When checking the integrity of the pressure line to the KLM computer, I bumped the DME plug partially off. It started once afterwards, but then I had a passenger get in and he rested his foot against the panel, pushing the plug out just enough that it wasn't connected.

Now on to the cycling valve.

Thanks!

chally72 · 04-03-2010, 05:00 PM

I've searched and read quite a bit more on this situation, so I'm going to update this post now.

My engine is definitely not going into safe/limp mode. When it does its little fuel cutoff deal, I can immediately jump back on the throttle and make it happen again. I don't have a crippled car that I have to turn the key off/on again to fix.

Now, it does backfire very loudly after this happens, which suggests to me that it has lost spark, not fuel. I saw ONE instance on this forum where a person mentioned offhand that this happened to him until he replaced the coil. I'll see how bad a coil is to obtain, and possibly check this tomorrow.

I couldn't believe the number of threads all with the same problem- hard cutoff at around 4000 RPMs under load, but no problem at all if the throttle is applied gently through the RPMs.

nynor · 04-03-2010, 09:18 PM

my car did this when i first bought it. it was the DME.

chally72 · 04-04-2010, 04:16 AM

Nynor, in searching this forum on the problem, I found one post by you that said your problem was the line from the J-boot to the cycling valve, one post that said it was the KLR, one that said it was a short in the wires to the knock sensor, and now one that says it is the DME. Did you have ALL of these problems?

nynor · 08:04 AM

Quote:

Originally Posted by chally72

Nynor, in searching this forum on the problem, I found one post by you that said your problem was the line from the J-boot to the cycling valve, one post that said it was the KLR, one that said it was a short in the wires to the knock sensor, and now one that says it is the DME. Did you have ALL of these problems?

yup, all of those problems. except the KLR, not sure where i said that, but it was the DME.

the SPECIFIC problem you describe where the engine cuts out and backfires, was the DME. mine would do this at about 5700 or 5800 RPM's. i replaced the DME and KLR at the same time because what i had to change it to was from an '86 and i wanted to keep the boxes together.

the wiring frayed at the knock sensor would put the car in limp mode and it would stay that way until i restarted the vehicle. eventually it just stayed in limp mode and i pulled the manifold to replace the knock sensor and found the wires were nearly severed.

the hoses under the manifold were all aged and either cracked or had loose hose fittings. this was causing all kinds of problems.

piperporsche180 · piperporsche180's Garage

I had a similar issue, it was a faulty KLR

ilikemy944 · 04-06-2010, 05:33 AM

TPS can cause this also. If it is the TPS it probably only happens at 80% and above throttle application.

nize · nize's Garage

what do the blink codes show?

nynor · 04-07-2010, 10:02 AM

Quote:

Originally Posted by nize

what do the blink codes show?

oh, boy. here we go....

chally72 · 04-07-2010, 03:38 PM

Nizo you blink code OCD'er, you'll be happy to know that those were the first things I checked, and it does not throw any codes.

I accidentally managed to get it to boost to around 8-9 lbs today with no cutoff, so it is a little inconsistent. I still don't think I've heard the wastegate open.

nynor · 04-07-2010, 03:49 PM

i don't think i have ever *heard* the wastegate open. if you have the stock exhaust, i don't think you'll be able to hear yours, either.

chally72 · 04-08-2010, 08:17 AM

If you look at the pictures above, you will see that the wastegate is vented to open air. So I'm assuming it will get pretty loud.

nynor · 04-08-2010, 11:29 AM

Quote:

Originally Posted by chally72

If you look at the pictures above, you will see that the wastegate is vented to open air. So I'm assuming it will get pretty loud.

only a fraction of your exhaust will exit via the wastegate. correct me if i am wrong.

nynor · 04-08-2010, 03:37 PM

so, i was looking at the pictures of your exhaust setup in the other thread. dude. i cannot imagine that you will get things working right with that crap. no offense.

my suggestion is that you set it all up stock, you will probably need to source some parts to replace the frankensteined stuff. go through all of your vacuum lines and intake hoses. get it running correctly, then start over and modify judiciously. just saying.

chip18 · 04-08-2010, 07:50 PM

What chip, is in it if any, what size fuel injectors are in it, do you have a 3 bar FPR? The PO might have just thrown a bigger turbo on it with out supporting mods?

If that's the case any boost over stock would trigger fuel cut.

chally72 · 04-09-2010, 02:49 AM

How can I tell what size injectors are in it?

And if I crack the cases on the DME and KLR computers, what am I looking for to tell me if the chips have been changed out?

How will I know I have a 3 bar FPR?

And Chip, it is not close to overboosting. I put an aftermarket boost gage on, and it pretty well agrees with the dash gage. I am getting 5-7 lbs of boost at most before this cutoff.

I will try to post pictures of the fuel rail and injector setup.

And Nynor, it is going to be very difficult to get it back to stock now. I really don't see a problem with the wastegate and turbo. As chip said, I will just have to make sure fuel delivery and chips match what is on there. A good few days replacing vacuum lines is the only other thing I'll have to do.

chip18 · 04-09-2010, 06:13 AM

Ok bar and psi I have a rough understanding off but I understand 1 bar to be 14.7 psi. I googled
1.2 bar and I get 17.2 psi! No way is it going to do that without help.

My Turbo S is chipped to run 18 psi on 91 octane and 20+ on race gas or E-85. Stuock turbo,3 bar AFPR, 55 lb injectors, 2.5 inch cat back and Max Performance chip.

So you said 1.2 bar that would be fuel cut, if it's hitting fuel cut at 5 or 7 psi that's much different!

Right now you need to quit boosting till you get it sorted out. The factory gauge doesn't tell you how much boost it's running, your after market boost gauge tells you that. The factory gauge just tells you when your hitting boost.

Do you have a wide band O2? What are your AFR's when this happens? If it's going lean at WOT, anything above 13 to 1 afr, your going to be replacing your head-gasket, if your lucky!

If it does indeed have an aftermarket turbo, you need to support it, with upgrades or replace it with a stock turbo.

You can check the fuel pressure at the rail with a fuel pressure gauge, you hook up the gauge and pull the vacuum line FP would be 44 psi with a 3 bar FPR.

But that means nothing with out knowing if the car is chipped. First step is look at the DME
most after market chips are marked. So that needs to be the first thing you do. If it's an aftermarket chip, then you need to determine what (the chip needs) if it's the stock chip and you have an aftermarket turbo, you need to replace the turbo with a stock one or support, the turbo, with proper mods.
But quit boosting now!