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'94 940 turbo starts then stalls

soggydonkey

soggydonkey

New member
Joined
Jul 8, 2016
Location
Nyack, NY
I'm hoping someone can help diagnose a stalling issue with a 1994 b230ft that recently had the head gasket replaced by a local mechanic. Had a mysterious slowly-disappearing coolant issue, then total head gasket failure in the driveway. The car never overheated. Engine has 120,000 miles on it.

Had the head gasket replaced, head decked at a machine shop, got it back and it ran like new for a week or so. Then my wife was driving to work and it stalled at a stop sign. No stumbling, she just rolled to a stop and it shut off. She restarted it, drove it home.

It sat for a week, then I restarted it to see exactly what happened. It started perfectly, idled around 1600 for a few seconds, then dropped down to 1000 for about five minutes with a little bit of surging, then stalled when I touched the gas pedal. I unplugged the idle control valve connector, started it again, did the same thing immediately after the fan kicked on.

I installed a new Bosch idle control valve, started it, and same thing happened. Here's a video -- the fan comes on, and then the engine just stalls, as if the ignition is turned off. For about a minute it will not restart, as if there's no spark. Then after a couple minutes it will restart as if nothings wrong.

Anyone know what I should look at next? Oxygen sensor? Fuel pump?

Any suggestions are most appreciated!

--Chandler
 
Thanks for the replies -- gonna start with the radio suppression relay and crank pos sensor when I get home. Will follow up.
 
I just bought a noid light from IPD for $5. Everbody here should have one. Don't throw parts darts!

soggydonkey said:
--
Anyone know what I should look at next? Oxygen sensor? Fuel pump?
Click to expand...


Get a test lamp. I use my $10 one on $100,000 cars all the time for basic diag.
 
Last edited:
ZVOLV said:
noid light from IPD for $5
Click to expand...

'Scuze my ignorance, but what's a noid light?

Crank position sensor & wire wiggling don't have any effect, having my mechanically-inclined buddy check the radio suppression relay and ignition amplifier next. Started and ran wonderfully this AM... for 10 minutes. Then just turned itself off again, this time before the fan kicked in. I was sure somehow the electrical load on the fan was causing a drop in volts somewhere else, but I guess not.
 
"Radio....relay" powers the injectors. A noid light is plugged into the fuel injector lead to check for fuel injector pulse.

Got a $5 test lamp? Build one if not. Check for power to the injectors with key on. Test lamp to fuel pump circuit when it's a no start.
 
My money is on a bad MAF, tough to test thoroughly, but it is an easy part to swap and find out if that is the culprit.

Unplug the current MAF, and try and start it, it should fire up, and when you touch the throttle it should bog, but at least try and run. (indicates it's probably good)

If the MAF is bad, when unplugged, it may start (or not) and if it does, when you touch the throttle it may flat out die, that's a good indicator the MAF is no longer healthy.

Easy test, report back
 
lummert said:
If your car has a tachometer note it's behavior before and during the issues.
Click to expand...

Almost imperceptible surging from about 1100 to 1200 rpm. Starts just like it always did, idles that way for 5-7 minutes, then tach just pegs at 0 as the engine stalls.
 
Check for spark when it won't start. Sounds like powerstage....

Test lamp between coil negative and ground. See if it blinks. This will check signal from powerstage to coil. No blink=no spark.

Or click my signature in my first reply.
 
ZVOLV said:
"Radio....relay" powers the injectors. A noid light is plugged into the fuel injector lead to check for fuel injector pulse.

Got a $5 test lamp? Build one if not. Check for power to the injectors with key on. Test lamp to fuel pump circuit when it's a no start.
Click to expand...

Okay, thanks -- this is my next move after checking the MAF. I'm getting a used-but-known-good one to swap.
 
soggydonkey said:
I ordered a new ebay $20 ignition amplifier just to see if swapping that out makes a difference. Won't get here 'til Friday tho.[/

I had better luck using a used Bosch power stage. I keep another used Bosch power stage as a spare. Aftermarket caused issues.
Click to expand...
 
Did you check for spark? It's a job you can do with no tools. Disconnect king lead and lay it close to a good ground and crank.


See my no start thread linked in my sig.

Tach INSTANTLY dropping to zero is also a solid indicator that sparked failed. That's the only reason I mentioned powerstage.

Here is my EZK analysis thread. Crank sensor signal to EZK box. 5V square wave from ezk box to powerstage. Then finally powerstage controls the ground side of the ignition coil. EeeeZK.

http://www.forums.turbobricks.com/showthread.php?t=322395
 
So just updating this in case anyone has similar issues:

It was the ignition module or amplifier. Runs like a champ now.

Thanks for all the help, yinz.
 
Nice. Thanks for posting back. I fixed my no start once with no diag tools by just swapping the powerstage also.
 
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