Problem

cyclemike · 02-04-2001, 03:28 PM

I've been running into a problem lately with my 87 951. I been driving it fairly hard lately and after driving for 15 or so minutes, when on full boost around 5K it feels like someone just slams on the breaks. I think i hear the wastegate cut pressure loose also. I'm not sure what is causing this, i did put an adjustable boost regulator on about 8 months ago. I did remember reading something about this a while back but please refresh my memory or add your thoughts, diagnosis's. Thanks

Mike

porscheboi928s/c944t/n · 02-04-2001, 07:33 PM

can u describe it more????..could be alot of things...i'm no expert but it could be ur gas filter(starves at high rpm)...is there a detonation??(u said at full boost).. could be the timing backing down(retarding)...it is very hard(for me) to diagnose ur car here on the forum.....these are just my diagnosis on ur car....and i can be very very wrong too!....just my 0.02 cents

todd951 · 02-05-2001, 11:28 AM

Do you still have your stock chips? It sounds to me like your ECU is cutting off the injectors (with the stock chips it cuts the fuel off when it senses an overboost condition). If you're running your boost controller at a higher than stock level without replacing the stock chips, then this almost certianly what is happening.

[This message has been edited by todd951 (edited 02-05-2001).]

cyclemike · 02-05-2001, 05:17 PM

That could be the problem, however I installed the boost enhancer out of the box which was set to stock boost I think. I'll definitely check to see what the enhancer is set at. I don't think I'm getting detonation. I recently replaced the fuel filter so I'm sure that isn't the cause of the problem. Is there anyway I can adjust the fuel regulation to see if this cures the problem, without buying a set of chips. I do think this is going in the right direction. I don't really know how to explain the problem other than it feels like someone hit the brakes for a second and then I can't accelerate. If I back off the throttle things return to normal until I get back on the gas hard and the boost and rev's go up again. Any more help or ideas would be greatly appreciated. Thanks.

Mike

Goku · Goku's Garage

It is definatly the boost regulator. I have a wastegate shim without chips. That is what happens when you overboost. Almost 100% that is the problem. It is a weird thing when it happens the first time, but as you know, it's not suddel. Well either get some chips, take out your boost controler, or learn to drive with it =).

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Goku Super Saiyan MCSE
88' 951
00' VW Golf 1.8L TURBO
Tonight I feel ambitious and so does my foot as it sinks on the pedal I press it to the floor...

drew1 · 02-05-2001, 05:33 PM

Don't know the rev limiter is operated, but sounds like something there.

drew1

todd951 · 02-05-2001, 05:44 PM

The Lindsey boost enhancer should not cause this at the stock setting. You've probably got something in your boost control system that isn't working properly. I had the same symptom in my 951 (with no mods), and it turned out that the cycling valve was bad. Your problem could be that, or it could be the wastegate, or it could be a bad connection between the KLR and cycling valve... You should probably take it to a reputable Porsche mechanic to diagnose the problem.

Walker944 · 02-05-2001, 05:49 PM

Cyclemike,

Go the http://porsche-944-garage.tripod.com/

Go in to the 944 Turbo FAQs, section 6.4

It sounds like your problem you have is an over-boost issue. Hope this helps.

--Mike

6.4 Turbo Overboosts

Problem statement: By far the biggest problem (at least so it seams) with my new 951 is that it cuts the fuel VERY abruptly during heavy acceleration. It is almost like someone is hitting the brakes! It usually happens around 4000rpm but will not occur if I just accelerate "normally". Also, my boost gauge is stuck at one when the engine is on (it returns to 0 when engine is turned off). I believe I can hear the turbo spinning during the acceleration so somehow the boost gauge must be connected wrong?

Second Problem statement: The car idles and runs fine, as long as you don't get on the boost hard. If you floor it, the boost gauge goes up to about 1.8, then, a couple of seconds later, the car jerks hard, and the boost goes away (fuel shut off??). I believe that either the cycling valve or the wastgate isn't working. Is there any way to check out which of these 2 items isn't working? Does anyone know of better designed parts to replace these?

Diagnosis 1: This is an overboost situation. One of the most common causes of overboost is the pressure line leading from the wastegate. A crack here will cause overboost for sure the DME then shuts off the fuel. This hose is rubber & can dry rot over time.

Diagnosis 2: You have a broken vacuum/boost line (hose) between the intake manifold between cylinders 3 and 4 and the KLR (Turbo control computer) box in the passenger footwell, or your KLR box is broken. If this hose is somehow cut or is leaking, the KLR will be reading atmospheric pressure, which will result in no real power for you. The KLR doesn't know how much boost, so goes into overboost protection mode (which is the abrupt cutoff of boost.)

Diagnosis 3: One possibility is that the connection to your air flow meter needs to be cleaned. The next is your wastegate is stuck. The next is that you have a leak in your lines going to the wastegate so that it doesn't measure the proper boost from the turbo and keeps letting boost build. Result: your DME/KLR will shut down the fuel so you don't blow your head gasket and you fly through the windshield. Inspect your hoses to and from the wastegate and cycling valve.

wolfrpi · 02-05-2001, 08:00 PM

I would definitly buy a set of chips for your car. Running too much boost with the stock settings is going to grenade your engine if you are not careful. The chips do many good things including increasing driveability and removing the boost limiter. My car runs so smooth now, I'm not sure if I want a MAF! Call Huntley Racing, they have great prices on chips. Also, get a real boost gauge...the dash gauges are electronic and are known to be very inaccurate.

Erick

86 951
87 924S

cyclemike · 02-06-2001, 03:41 PM

Thanks for the replys guys. I think I'm going to order a set of chips and see if that changes things. I've been meaning to get around to ordering the chips anyway. Now of course, the next logical question, which chips for my 87 951? Go ahead, hash it out. Thanks again for your replys.

Mike

todd951 · 02-06-2001, 09:20 PM

I think you should hold off on the chips until you get your overboost problem fixed. The ECU is cutting the fuel off to protect the engine, so if you remove that protection by getting aftermarket chips without correcting the overboost problem, you could break something.

1.2gees · 1.2gees's Garage

Todd, it sounds to me like he wants to break something... Err, he wants the overboost...

That's what an adjustible boost controller is for isn't it?

Try backing off the boost a little! You're likely to blow your head gasket, before anything else, unless you get detonation. Chips will make the car run a little richer, and back off the timing a bit too, however may let the boost go a bit higher than the rest of the engine might cope with!

The proper way to make sure you don't get detonation would be by controlling your timing, and running the engine a bit cooler (you use more fuel to do that, anti-freeze temp doesn't affect cylinder head temps too much!)

And the way to do that (IMO) would be higher fuel pressure, then possibly (but not likely) larger injectors. An air/fuel ratio meter would probably be another welcome addition.

For the time being, try backing off the boost (from your adjustible controller).
Ahmet

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It's all the driver...

wolfrpi · 02-06-2001, 11:16 PM

Todd, I think mike is not sure what the boost enhancer is set to. Even so, I would reccomend disconnecting the cycling valve and running a manual boost controller to make SURE that the engine does not overboost.

Erick

todd951 · 02-07-2001, 05:46 AM

The boost enhancer is not intended to be a controller, and is not easily adjusted. I was under the impression that he installed it out of the box without changing the facotry setting, which is 10psi, so it shouldn't be affecting the maximum boost pressure at all. A boost controller *controls* the boost, but if the wastegate or cycling valve or something isn't working, then he doesn't have any *control* over the boost, which is why I say he should fix it.