Ive used the forum many times, i have searched and found nothing to answer my question.

I have a 91 740 turbo 117xxx miles, the car is amazing drives great, boost is good, however when i give the car some gas and depress the gas pedal past a certain point the car is sutting out. This usually happens around 3500 to 4000 rpms. This shut down feels like the computer is shutting the car down. if i drive the car normal its accelerates fine shifts great and no other problems. I noticed this problem when trying to pass on the highway. Also if i have the car in neutral i can rev the car freely. im stumped, this only happens when driving. I checked the turbo piping for leaks and everything seems fine.


Is there a safe mode the car can be in? Is there a boost or turbo relay?

One more question, there is a fan in front of the intercooler, is that supposed to be on all the time? I dont think mine comes on; could that be a heat issue and why the car shuts down when pushed. Thanks

 

30 views and no help.....am i the only one to ever have this problem.

 

First, the fan.

It's an auxiliary fan. It only comes on when the coolant in the radiator reaches a certain temperature. So the times it should come on is when the car is idling on a hot day when the engine is good and hot. It's on only when it needs to be. Now, on my car is melted the fuse panel and I had to rewire another fuse. I've also had the switch burn up in the radiator. I replaced all that and now is works great. You can rewire it to come on with the AC, but unless you live in Texas or some place hot like that, it won't help much. So if you stop your car, before you turn it off you should see it start if it sits idling for long enough. Also, check your fuse panel for the auxiliary fan fuse and see if it is intact. If the fan's bearings go bad then it will start blowing fuses.

I would pop-off my distributor and check it for condensation, cracks or eroded electrical surfaces. Also, have you changed the plug wires? Check the plug gap as well. If it's too difficult for the spark to jump the gaps in the system, large fuel in puts will stop the spark from jumping the gap.

Now if the car is boosting more than normal, then it's the charge over pressure switch actuating. This happens around 14 psi (these cars are only supposed to boost to around 7psi). The car should be way powerful before it cuts out. If that is the case, the pressure line to the waste gate actuator fell off, has a hole or the waste gate is stuck. But I think that is a little unlikely because you would notice an increase in power since this problem showed up.

Good luck, I hope that all made sense.

 

Thanks for the help, im gonna look into the waste gate and the hoses around it.

 

Your car doesn't use a over pressure switch,they used those on LH2.2 yours is a LH2.4.

First check your tune up items as Titan Joe suggested.

If your car is missing under boost and black smoking out of the tail pipe you probably have an inter cooler hose torn.
Remove the pass side inter cooler hose and check the underside,they usually split close to the inter cooler.
Is the ces light on?

 

Wow...a torn i/c hose usually is noticible whether or not you're under boost. The very first thing I'd do is check the air filter to turbo hose. These get oil soaked and age. What happens, you go into boost and the hose starts collapsing...they can suck flat! The easiest way to check it is to have someone put it in reverse and power brake it so it will go into boost. If you see the hose flex inward at all...it's toast. WORD OF CAUTION: Make certain it's someone you trust and make sure they are in REVERSE and that there is nothing EXPENSIVE behind the car!!
You're not pulling enough rpm's to hit the 6500 rpm rev limiter and unless your boost limiter has been bypassed you're not hitting fuel cut.
The aux fan? It's a joke...by the time it comes on you're boiling over. I DO live in Texas and so they are wired in w/ my a/c compressor.

 

Thanks for all the help....ive only had the car for two weeks so i wouldnt know the difference in boost pressure, but it seems like as i accelerate the boost needle goes pretty high pretty fast. I have a 91 so i have the newer gauge under the tach. when the car cuts out that boost needle is 3/4 the way to the right or maybe a little more and thats around 4000-4500 rpms. Thats when the car cuts out. Im saying i beat on the car and constantly rev it out. This is my commuter car and one day i happened to give it gas to pass someone and noticed it. Not sure if it helps, and im also gonna do the power brake test to check the ic piping.

 

I guarantee if you spend a Saturday under the hood you'll find one or more bad hoses not to mention a nasty air filter. Remember, on a turbo car, vacuum hoses pull double duty...vacuum under normal operation and positive pressure under boost. If you look, you will see small clamps on the ends of the small vac hoses. That's so they don't fly off!
You have a car that has the potential to be wicked fast once you get it past stage zero. Right now, you need to give it some tlc and take care of the little stuff other owners neglected.

 

thanks everyone for your help...i did a closer look under the hood and saw my air box was missing a clamp and air was leaking out.....i changed out the box for a cone filter and problem solved. Thanks again this is a great resource for volvo information.