# POOR COMPRESSION 1 2 3



## vj5256 (Oct 20, 2009)

Help guys, I'm about to blow a gasket. So I pick up this s4 with 64k miles online and It runs like poop







It seams to missfire and backfire a bunch. I vag the engine and it says missfire 1 and 3. So I check compression and it is weak on the drivers side. I then check the timing belt and it definitely looks correct. I have been doing a bunch of reading and it appears a bad temp sensor caused it to dump fuel in that side and wash the cylinders. They vary from 25 to 75 lbs. 4 5 and 6 I think were 125 to 150lbs. At one point early on cylinder 2 was at 125+ but now its down to 50.
So how do I get my compression back, or do you think maybe it's something else?
fyi ... yes I will replace the belt soon, but right now I need to get it running first


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## JBallou (Jan 6, 2009)

*Re: POOR COMPRESSION 1 2 3 (vj5256)*

Sounds like you have a few prob;ems. First any idea what caused the fuel wash? the compression issue can be delt with, with a small amount of oil down each cylinder to seal the piston rings.
Might need to do that first to get it running, with new spark plugs in order to find out what caused it in the first place. Then set about diagnosing the missfire/wash issue.
Cars that run are sometimes easier to diagnose.


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## Peter Badore (Jun 17, 2002)

*Re: POOR COMPRESSION 1 2 3 (JBallou)*

The valves are probably bent. Someone have have reset the timing belt after the belt skipped from a crash or lack of maintenance, but the valves stay bent. Fuel wash is probably not the cause of the very low compression you reported.


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## vj5256 (Oct 20, 2009)

I dont think they are bent, but always possible. I am airing out the cylinders for a couple days then putting in new plugs. The other cylinders have from 175 to 200psi. I will unplug injectors and see what the preasure is tomorrow. Is there and easier way than uplugging the injectors to keep it from pumping in more fuel, like maybe the cams sensors?


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## Peter Badore (Jun 17, 2002)

*Re: (vj5256)*

You could do a leak down test to see if the valves are bent. I have worked on many Audi V6 
engine cars and own two 2.7l biturbos. The low compression that you are seeing is typically caused by bent valves. As for stopping the fuel flow from the injectors just remove the combination relay for the fuel pump and the injectors it is code number 208 in the relay panel.
first row.


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## vj5256 (Oct 20, 2009)

So I let it sit for a couple days and also put some oil in the cylinders. Notta... nothing ...







Guess I am pulling the head tonight. I think the intake valves on that side are bent.


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## Peter Badore (Jun 17, 2002)

*Re: (vj5256)*

Are you pulling both cylinder heads? There can be slight leakage from a minor valve to piston impact. I would carefully check all valves in both and "when in doubt toss it out" as the 2.7l biturbo takes lot of time and effort to repair. Just my opinion, but we worked on an Allroad 2.7l biturbo that needed 3 complete engines in 6 weeks to get it right from all the mistakes made by the prior repair attempts.


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## vj5256 (Oct 20, 2009)

*Re: (Peter Badore)*

3 engines in 6 weeks is just crazy. I pulled the head and yes, one intake valve was bent in each cylinder, and barely bent at that which is why it would still build a little compression, but not enough to run. Obviously the belt had jumped one tooth and it just clipped the outside intake valve. I will replace the bent valves and put the head back on. Any suggestion on where to get a cam holder or other thing to do while apart.


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## Peter Badore (Jun 17, 2002)

*Re: (vj5256)*

I have all the tools. You can also rent them from some online parts suppliers.


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## vj5256 (Oct 20, 2009)

hey I see you have an 89 944 .... we should see how it does against my 89 928








Oh yeah maybe can I borrow your alignment tool after my 928 woops ya ... haha


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## Peter Badore (Jun 17, 2002)

*Re: (vj5256)*

Ok. When did your 928 S4 have its timing belt and chain pads changed last?


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## vj5256 (Oct 20, 2009)

*Re: (Peter Badore)*

I don't know. Why do you ask, you looking for some work? I have only had the car a short time. I was plan to do a teardown this winter. I am going to supercharge or turbo it. Thinking I will also replace the clutch, and engine seals while I'm at it, it definitely has a case of the oil spots.


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## Peter Badore (Jun 17, 2002)

*Re: (vj5256)*

Because the timing belt and chain pads are weak/failure areas in the 4V/cylinder Porsche 944S and 928 32 valve engines. No i don't need work just look at my partial car list. Also the last 928 4V V8 I worked on required an engine pull to remove the cylinder heads--not a maintenance friendly design--that engine was the first year of the 5.0 928 4v which was changed by the time your 928S4 was introduced.


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## vj5256 (Oct 20, 2009)

*Re: (Peter Badore)*

turned out to be bent valves







1 valve in each cylinder was bent just a pinch. 3 new valves and a new head gasket and she's ripping down the road. and that porsche s4 is getting supercharged this winter ... see ya...


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