Ather

My 87 S4 has not been running on peak performance since the day I got it which has been a few months ago. It currently has 127k miles. I did a compression test a while ago and the results were not the best. The compression numbers are 175, 145, 160, 160, 174, 80, 90, 105. Another problem the car has, that it doesn't start without me pumping the gas a couple times before turning the car. It just cranks and nothing happens. After starting, it hunts for a couple of seconds but idles smoothly after that. After doing some research it sounds like some of the potential causes could be one of these or a combination of them:

1. Bad MAF
2. Bad Computer
3. Bad Injectors and O rings
4. Bad distributors and ignition wires
5. Bad plugs
6. Bad sensors (hall, knock, temp or O2)
7. Bad fuel lines
8. Bad Fuel pressure regulator.

I am sure I am forgetting some. Considering the lower combustion issue, I am inclined to think it could be the injectors, and ignition wires but not 100% sure. I should also point out that the car previously had a "small" engine fire which was repaired by the previous owner.

I have purchased new plugs which I will put in this week but wanted to get an idea what I should tackle next after that. Any thoughts or suggestions would be greatly appreciated.
Thanks,
Ather

Speedtoys

Entire intake and sensor refresh...

Do a wet compression test..what happens to those low cylinders?

Exactly a year ago with my 88S4, I was in similar shape...it "ran" albeit really really ****ty.

Nothing short of the FULL intake refresh got it right, and thru smog. (plus new cats, new o2 sensor..)

Jim M.

I'd do a leak down check to determine if the low compression is rings or valves. On a 928 the engine should be warm/hot before doing a compression check. Then as Speedtoys says a FULL intake refresh with either new or re-built injectors.

Ather

Okay thanks guys. Sounds like I have big job on my hands. Not sure how to do a leak down test. Will have to look that up.

Speedtoys

I did a full intake refresh with one good arm last winter.

Wasnt so bad...you'll learn a lot.

Speedtoys

Yannow...

Id bet, that if you had -all- the bits...and a good toolbox..

Three people could to a full intake refresh at Sharktoberfest in under 2hrs.

Ather

Hi Speedtoys, thanks for the encouraging words. I'm not that good with a wrench but I will definitely take it on. I've downloaded the legendary Intake Refresh post from Dwayne.
Aside from the sensors, what else should I be changing, cleaning or updating?
Thanks very much,
Ather

Speedtoys

Everything you put your fingers on that senses, measures, or attached to something else.

You can add a few weeks to the project, by getting powder coating, cad plating...etc..etc..or just pull apart, clean, and re-assemble in one long weekend or two.


FWIW: I will come help when time allows. My weekends are a disaster (all stuffed for a month at least)..but stoppin by after work to guide..sure.

vincer77

Are the cylinders with low compression adjacent yo each other? If so could be head gasket or warped head

kelanel

just thinking the same thing unless he's listing the cylinders in firing order lol

leakdown should reveal that if im not mistaken though.

James Bailey

Those compression numbers are terrible ! At anything under about 100 PSI that cylinder will NEVER fire and run close to right. Before doing ANYTHING else, spending more time and money, figure out what is causing the low numbers. If it is valves that is a big job, if it is a pistons/rings/cylinder issue the engine would need a COMPLETE rebuild...
The fact that the engine was on fire leads to the question HOW was the fire exstinguished ? Was water used and did it get into the cylinders and attack the pistons rings and cylinders ? How long was it parked ? Was it smogged when you bought it ?
Doing the intake overhaul could easily be a total waste of time and you may need a different engine.
How many miles have you driven it since you bought it ??

Speedtoys

Good points...re-run a compression test with some oil in each cylinder.


SOMEDAY for the hell of it, I'll do a leak down test like Continental does it on their engines..its pretty cool.

The GOOD news, is that 1/2 off engines for Xmas will be available soon.

Ather

Yeah the numbers don't good at all. I will try doing some additional testing on the cylinders. Not sure how the fire was extinguished. It was a salvage car which the previous owner bought and repaired supposedly. He had it for a couple of years and drove it very sparingly as he had another 928. I have driven 4k miles on it in the last 5 months. Drove it home from AZ to CA and then registered it. It failed the first smog and then I put a bunch of fuel injector cleaner and then it barely passed the retest.

Ather

When and where is Sharktoberfest by the way? Would really like to attend and meet the local members. I recently joined the norcal928 list so I'm guessing there will be some notifications sent out...

Speedtoys

http://www.sharktoberfest.com/home.html