SummitP

Hi Guys, my 89 951 is running rich under boost. Idle is spot on when warmed up, whether I have the 02 sensor plugged in or not. It may go to 14.5 or so with it unplugged, but hovers right around 14.6-8 when plugged in. Tells me 02 sensor is working.
I did notice today, my idle stuck lean, 17ish for a while, but then a little later, ran back at the 14.7 range. It again stuck lean a little bit, but then went back to normal.
When I roll to a stop, it will drop idle below 800rpm, down to 500 or so, for second, and then comes back up to 800. Vacuum appears good... (will get the number tomorrow)
Bad ICV? But pressure test holds...

I have replaced all the vacuum lines on the car, replaced the intercooler hoses, (old and stiff black ones with silicon from LR). When I pressure tested, I found a leak at the thermo vacuum valve. replaced that. Can't find any leaks anymore. I am pressure testing with the copper arnnworx cap at the intercooler intake.

I recently replaced the clutch and cleaned the bellhousing grounds. I also checked the cable condition by cutting back the insulation and checking the cables out, they are clean clean clean, look new. When I check for positive voltage from the negative battery terminal and my various ground points, I get 0.00-0.01v. I have not checked ground under the dash...
So basically I think my grounds are solid (except the under the dash one).
My voltage at idle at the battery is 13.4v. Shouldn't it be a bit higher? Alternator crapped the bed a while ago, and I had it rebuilt with a new voltage regulator installed.

I have a recently rebuilt 26/8 from evergreen turbo. I replaced the AOS seals while I was in there. All new sealing rings in the exhaust. I also rebuilt the throttle body with new seals when I had everything apart. New heater control valve was installed as well.

Set up is a vitesse MAF+ kit, with the map sensor. again, all new vacuum lines everywhere. Recently cleaned the maf sensor with sensor cleaner.

Bypass valve was replaced.

ECM temp sensor is relatively new.

I tossed a Fuel pressure gauge on the end of the rail, and it reads right around 40psi at idle. Pressure holds for a while after I shut it off. Fuel filter has about 10k on it.

Car has 150k on it. I did find this the other day... pulled a plug, and it had oil on the threads. I check the other 3, and they did as well. I read that might be valve seals? but then wouldn't the car smoke on startup? It does not... Could that also lead to running rich? Car sat a while during the clutch change, but was showing rich symptoms prior to clutch change.

Car boosts well, but goes to around 10.7 afr under boost. If I flip over to FQS switch position 2, to pull fuel, it will idle lean. Should be set to 0 per Vitesse, (and ran fine for a while there after the vitesse install.)

Could the brake booster fitting be leaking? But isn;t that a check valve? pulls vacuum, but no pressure into booster?

Any input is welcome.... Thanks guys.

ealoken

My car had the same issue, 9,8-10,8 when boost, but my head had a massive oil leak, valve seals totaly worn out.

Is your car burning oil?

SummitP

It doesn't seem to be really burning oil. My thought about the valve seals was based on something I read here about valve seals being the cause of the oil I found on the spark plug threads.
And mine never gets as rich as 9.x, but does go down to 10.8, 10.6 on occasion.

ealoken

OK, at worst i burned 1 L oil on 100 L gasoline..

SummitP

Did doing your valve seals solve your running rich problem?

Haha, that ratio means nothing to me. I use about a quart every 7-800 miles. So yeah, it eats some oil, but I've seen worse.

ealoken

Ill find out in 4 weeks, getting the engine together and re dynoed.
But i have a new ECU system, no MAf, and a lot of changes.

SummitP

figured out the oil on the spark plugs, and I'm a bit of a knuckle head on that one... I had put a dab of oil in each cylinder prior to startup a while back, cranked engine over manually, and then put the plugs back in. doh.

peanut

when you had the fuel pressure gauge on the rail did you check to see if the FPR was working properly ?
The vacuum system should reduce the fuel pressure by 0.5 Bar or so at idle and increase it up to the max of the FPR which is 3.25Bar on mine when the engine rpm is raised and held for a while.

Check carefully for any fuel in the vacuum system causing a rich mixture. My FPR was leaking intermittently which I only found by accident when running the engine with the FPR vacuum connector pulled off.

Your fluctuating idle could be caused by the ECU varying the additional air flow through your IAC valve to compensate for the rich idle mixture which can set up a constant fluctuating idle if the rich mixture is extreme as mine was

SummitP

I will check the FPR. It should be good, but should doesn't mean is, it was a new 3 bar fpr when I installed the Vitesse system. The idle does not fluctuate constantly, occasionally it runs real lean, 16, 17, but most of the time, it just settles in at about 800, and it will start rich when cold, but pretty smoothly will go to 14.7 as it warms up.

SummitP

So drove it around today, and got to diagnose a lean idle condition. Fuel pressure gauge was bouncing down at a regular interval. When I checked it before I started seeing this lean idle situation, it was steady and right around 40psi. Now it dips at a regular interval down about 5psi.
No fuel in the vacuum line at the fpr.
Sprayed a bunch of points with carb cleaner and saw no change in idle.

peanut

if your fuel pressure is dipping down that low its a miracle the engine runs at all.
The injectors require a certain fuel pressure in order to function.

It has to be an intermittant FPR I should have thought.

Porsche FPR are very expensive but it is a little known fact that late models at least have the option of fitting 2x different types of FPR.

If you disconnect the flow line at the inner front wing you will find that there are two connection options , an AN6 nut or a hose spigot which is normally hidden by the oem Porsche hose.

I recently removed the flow line from wing to fuel rail and connected a short piece of fuel hose to the spigot which allowed me to fit a regular type FPR at a fraction of the cost of a Porsche FPR.

I fitted a used a VW Golf GTi FPR costing $15 off ebay but a Corrado and others will fit . As long as it will maintain 2.5 BAR it will work fine.

So instead of the original Porsche 944S2 FPR with a nut type fitting you can also fit any 2.5-3.0 BAR FPR with a double spigot fitting

SummitP

The fuel pressure is only dipping a few psi for a fraction of a second, and then stable, then dip again, then stable, then dip, kind of a like a needle that bounces every second just for a fraction of a second.
Fuel pressure behaves like this. When cold, it is stable, car starts easily, pressure is stable, afrs are rich (as they should be at cold start). At operating temp, the fuel pressure does that dip of a few psi every second or so. Very regular.
I drove it today and this morning after warming it up, it ran fine, but rich on boost. My AFRs are also a little rich when I start to apply throttle, maybe 12, and when I get into boost, goes richer, down to about 10.5.
I did try disabling the icv at lunch with a jumper cable, and the car ran fine like that too. But no change to afr under boost. Seemed like it ran better for a while, but once it got up to temp, it was rich again.
With the icv disabled, or enabled, vacuum at idle is -380mm/hg, or -15in/hg, at 4700ft altitude. So that looks ok to me.
It holds boost to 14psi just fine, and pulls well, but definitely running too rich at about 10.5-10.8.
Thinking about testing the DME temp sensor and wiring, maybe it is corroded, and providing too much resistance?

just a reminder, vitesse maf+ and recently rebuilt k26/8.

fast951

The fuel fluctuations may be an issue with the gauge. You have 2 different issues, fuel pressure dip and rich under boost. May not be related..

If the AFRs are rich "only under boost", you have a pressure leak. The only way to find it is by performing a pressure test. Good vacuum, does not mean there is no pressure leak. A proper pressure leak test includes turbo outlet hose, IC,... not just the intake.

If you are running V-MAF+ software, and it detects a faulty MAP sensor, it'll go into "limp mode", which defaults to extra rich under boost. However, the driver gets warnings when in limp mode, so you would know. Limp mode testing is detailed in the supplied instructions.

If the AFRs are rich all over, which does not seem to be the case here due to your good idle AFRs, then I would check numerous things: MAF ground, FQS, FP, Eng Temp....

SummitP

John, you are a gentleman and a scholar, and I am always amazed at the level of support you go to to keep people running your equipment happy. I did pressure test about a month ago when I finished up the clutch job, and I did find a leak at the thermo vacuum valve. I replaced it.
I did not get around to doing a pressure test this afternoon, but as it has not been driven a lot this spring, I gave it a little bit of an Italian tune up on the way home from work, and it ran with Afr around 11 or so. It is running better than it did before the clutch job. I did a thorough ground cleaning at the bellhousing when I did the clutch, and cut open the insulation on the ground cable to inspect, and it looks like new. I have done a positive voltage test across multiple ground locations and get like 0.01v on a digital vm.
I'll report back again after I do a proper pressure test with the car warm. I'd also like to do a test of the due temp gauge.
Thanks for the help.

peanut

that constant regular idle fluctuation has to be due to the ECU using the ICV to adjust for a rich mixture. Its a classic symptom.

The ECU is sensing that there is a rich mixture and opens the ICV to compensate and attempt to bring the mixture back to a stoichiometric ratio.

The mixture then goes too weak so the ECU closes the ICV and this sets up a constant over compensation by the ECU for the rich mixture which sets up the cycling idle rpm.

I would concentrate on the components that you have changed (MAF) and others that can cause a rich mixture. leaking injectors , leaking FPR .