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940 Turbo, random hesitation - fuel troubleshooting?

fatcatbestcat

Professional Hack
Joined
Oct 1, 2019
Location
Mississauga, ON (Canada)
Hey, it's me again.

This has almost certainly been covered a few times, but the Google machine keeps giving me conflicting answers.

I'm driving my '91 940 Turbo daily right now, and have had zero issues for the first thousand miles or so I've put on it. Just now running into one, though.

On my commute from work yesterday, I start getting a hesitation at various RPMs. A cough, and then it just keeps running. Eventually I get one bad enough to completely stall the car. Pulled over to see if anything important was broken, and couldn't see anything obvious. Made it the rest of the way home, coughing a few more times. I get it home, let it sit and cool off for an hour and suddenly the issue is gone. Drove it to work today and couldn't replicate the stumble or hesitation I was experiencing yesterday.

This is with a practically full tank, only driven 41 miles since my last fill-up. I've got a few days to work on it, anything out of the ordinary I should check out?

I'm going to be making sure my fuel pump works and replacing the relay anyway. It's got a cone filter on the intake, which is a little dirty - I'll be putting the stock airbox back on, but I'm a little doubtful that has anything to do with my problem.

If anyone has any other advice, please let me know. And if you could recommend a part # for a good replacement pump, that would also be helpful. Lots of conflicting info there, too.

Thanks!
 
I agree that this sounds like a fuel issue, but how's your maf? A buddy of mine recently bought a 740 wagon that had weird hesitations all over the place. Looked under the hood and the maf was a pro parts sweden unit. Tossed in a bosch one and it was back to normal.
 
I agree that this sounds like a fuel issue, but how's your maf? A buddy of mine recently bought a 740 wagon that had weird hesitations all over the place. Looked under the hood and the maf was a pro parts sweden unit. Tossed in a bosch one and it was back to normal.
MAF is something I've suspected but the one in the car is a newer Bosch unit. The dirty cone filter right next to it probably isn't helping, I'm going to swap back to the OEM box, OEM filter and blast the MAF itself with cleaner to see if that helps. A good uses MAF isn't something I can really get on short notice.

The problem went away so I'm not really sure what/how to check now. If the pump seems to work okay, I'm thinking about replacing the filter and running some fuel system cleaner through it.
 
Okay - an update on this. Fixed?

On a whim, I took the MAF off - and then promptly broke the ceramic temperature probe while trying to clean it. Got a spare used MAF, cleaned it out, and reinstalled it with the factory airbox and a new filter. Car fires right up, and no stumble so far.

Going to take it to work and monitor things to see if the MAF was the fix all along.
 
Hey, it's me again.

This has almost certainly been covered a few times, but the Google machine keeps giving me conflicting answers.

I'm driving my '91 940 Turbo daily right now, and have had zero issues for the first thousand miles or so I've put on it. Just now running into one, though.

On my commute from work yesterday, I start getting a hesitation at various RPMs. A cough, and then it just keeps running. Eventually I get one bad enough to completely stall the car. Pulled over to see if anything important was broken, and couldn't see anything obvious. Made it the rest of the way home, coughing a few more times. I get it home, let it sit and cool off for an hour and suddenly the issue is gone. Drove it to work today and couldn't replicate the stumble or hesitation I was experiencing yesterday.

This is with a practically full tank, only driven 41 miles since my last fill-up. I've got a few days to work on it, anything out of the ordinary I should check out?

I'm going to be making sure my fuel pump works and replacing the relay anyway. It's got a cone filter on the intake, which is a little dirty - I'll be putting the stock airbox back on, but I'm a little doubtful that has anything to do with my problem.

If anyone has any other advice, please let me know. And if you could recommend a part # for a good replacement pump, that would also be helpful. Lots of conflicting info there, too.

Thanks!
I've recently been having a similar issue with mine, it seems to only happen when going around a corner but it happens at any speed/RPM. I assumed it was wiring for the fuel pump, was the MAF the actual issue all along?
 
I've recently been having a similar issue with mine, it seems to only happen when going around a corner but it happens at any speed/RPM. I assumed it was wiring for the fuel pump, was the MAF the actual issue all along?
Yes, swapping to a clean, known good MAF and the stock airbox and new air filter cleared up the issue. Car also gained a few MPGs as a result.

Coincidentally, I ran into a few stumbles yesterday on my ride home - it's been obscenely hot this week, so if cooler weather doesn't make it go away, I'm going to put fuel system cleaner back in the tank and clean or replace the MAF since I panic ordered a second spare back in May when I first started having problems.

I'm starting to suspect the PCV is clogged and letting nasty goop cover the MAF.
 
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