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Won't boost, misfires, stalling, hard start.

ZVOLV

<Master Tech>
Joined
Nov 19, 2002
Location
California
1990 940 Turbo. I just did the head gasket.

UPDATE: Fixed It! I found a loose hose clamp at the throttle body.

I can usually get the car to start after excessive cranking and I even drove it for 20 miles but it just would fall on its face when I got into boost realm.

Stalls at stops and misfires a bit at idle and won't really stay running on its own.

I'm gonna give it the full shakedown but this is just a side job in somebody's driveway far from home or the shop so my resources and patience are limited. Especially after working all day and messing with this thing Iin the dark on the drive home.


-Starts and runs but you can't really drive it
-stalls and sometimes won't even restart.
-when it is drive able it won't boost
-misfires at idle and stalls after a bit
-compression is all above 130-150 or so on all 4.
-no codes yet
-runs worse with maf unplugged
-no change with temp sensor unplugged
-doing a cylinder drop test it usually stalls and Def drives worse with a cylinder disabled. Doesn't matter which.


I don't have all the answers guys. I cam probably get it sorted out with time but just seeing what kinda ideas you guys throw at me as far as where/how to diag.
 
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I asked my lead tech and he says to start with a running compression test and vac test. I really have a feeling the lower end is toast. It got so hot it melted the timing cover, burned a hole in the head between two cylinders.

A leak down test was also suggested.


Cranking compression seemed a little bit lower on the middle holes and they are the suspect ones.

The misfire at idle is a big clue to me that it's not something like a boost leak.
 
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I think they drove it much further than I thought while hot. People lie about this things.
 
I'm sure you have already done this and have suggested this trick multiple times, but have you checked the plug wires by spraying them with water? The only reason why I say this is because prior to my head gasket blowing and overheating, I had just replaced the wires with brand new Bougicords (which never did fit quite right in the first place). Well, after installing the new head gasket, it didn't seem to run any better, and after throwing more parts at it, I decided to spray down the plug wires and start the car at night. As soon as it started, I could see numerous blue arcs of electricity!

Upon further inspection, I noticed that some of the insulation on the Bougicord set had been mis-formed from the excessive heat causing the electrical energy to pass.

They've since been replaced and the damp/cold start problems/ hesitation are gone.

You state that the timing cover was melted. Could other components in the area too be suffering from some melting? Just a guess, and I hope that you are able to fix it in a speedy manner!
 
^^^^Thank you. Today was lots of wrenching. Trans services, oil changes, some light diag, and I finally got the pitman arm off a 4 runner steering box after 4 days of attempts with pullers, torches, air hammers and finally full body swings with the mini sledge got it off! I don't give up easily!


Why did you even re used that engine if it over heated that bad?

I don't run into this problem very often and when I do, we usually replace the whole engine with a used one with a warranty for this exact reason. I'm just helping out a good buddy and we took a chance and I have a feeling its not going to pay off this time.


I'm asking you guys for diag suggestions. B ' s will end up on th IL.
 
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Ignition components are suspect but I don't/try not to, throw parts at a problem anymore. I could see sparking in the dist but not sure if it was the spark just jumping the gap.

I even reused the old plugs but I probably shouldn't have.

Looking at the old head tonight with my 40 year veteran tech he said he had never seen a head melted thru between two cylinders like that before! He gave me a couple other ideas

I usually get a car to start on the first try after a big job. This one'sstarts but just has no power and dies all the time. I checked for airleaks. Airleaks would cause the no boost but not the misfire at idle. The car does surge at idle sometimes but really really ddoesn't act like an airleak.

Ha, last head gasket job I did at the shop was on a Subaru and first try oil sprayed everywhere from the HG. THIS can be put on upside down and the oil passage had no gasket material and it made a big mess
 
I put a an 88 760 back together that blew molten aluminum into the exhaust manifold. It had burned thru the combustion chamber wall and the only thing left near the exhaust valve was the seat. It alsomelted the timing cover, possibly, I forget, but THAT one ran after a head swap.

old $1000 car....meh...it's worth tossing a junkyard head at it to see what happens.


Short of popping a piston out, what would you tbrickers do to test the bottom end?
 
miln2309-20.jpg

http://www.cpomilwaukee.com/milwauk...qLeNQkX5PzGpNq_kTSBMdtZ8t8QUWAm6H6BoC2NPw_wcB
$104
 
I've seen EXACTLY what you described Zach, got a pic of the head on my phone. Guy drove the car (91 745T) for several hundred miles, said it was making a weird noise but drove okay. Finally caught on fire at the gas station what mocha spewed from the coolant tank onto a hot turbo.

The root cause...running uber-lean from a dead in-tank and dying main.

I'll second the scope on the plug wires. Also clean the RSR, and check fuel pressure.

You already check the AMM-turbo hose that always melts? Vacuum leaks?
 
Thanks Gselss.

This thing won't even rev in neutral without sputtering on the snap. Its way worse than a vac leak. Heck, I dunno if it even runs anymore! It even made some nasty clacking noises when I first started it.

I'm gonna try ether to rule out anything fuel related. It has no test port for fuel pressure but I could get a rig going.
 
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