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Discussion Starter · #1 ·
Hi, I recently got a 1992 940 with the b230ft 8valve. It has a problem that I can’t figure out.. according to my manual it is supposed to idle at 750 rpm. And when I start it and warm it up it runs like it should. But after it’s hot and been driven around it will pulse at idle from 750-500. it will be at 750 And it sounds like the engine is about to die until it hits 500, then the engine picks up again to 750, and starts to die again, it happens rapidly.. the other part is that when your driving and you accelerate hard enough to get into the boost, then slam on the breaks the car will die. It does not happen if your cruising and slam on the breaks, and it does not happen when you break for corners or slow down moderately. It’s only when the boost is high then the breaks are slammed. It also dies when your in drive creeping forward without any giving any throttle and turn. It seems to me like the power steering pump is putting more strain on the engine that is idling bad to begin with. All this happens with the A/C pump on or off... So in my attempts to fix this I started with a new battery, spark plugs, and wires. Nothing changed. Then I noticed the throttle body adjuster screw was cranked all the way open to keep the throttle plate as far open as it could be, I adjusted it to the middle and all the way down, and the lower I went the worse the engine would idle and made it easier to kill when driving, so I cranked the screw all the way back up how it was. Then I inspected all the vacuum lines, and I was satisfied with that. I tested with a vacuum gage. And the pressure was low so I suspected the valves were off. According to my manual they should be between .014-.018 all but one was within tolerance. cylinder 2 exhaust valve was .010. I don't have the tool to adjust these and I don’t believe that is the source of my problem. My next thought was that the throttle plate had a buildup around it keeping it from closing all the way and I was still suspicious about the adjuster screw. So I took the intake apart and cleaned the throttle body (that had no build up) and the manifold. I also checked my injectors with a multimeter and they all had the same resistance. I put it all back together.. and still no chance. I cleaned off the MAF sensor with parts cleaner as well wondering if it was too dirty to do its job, and again the problem is still there. I think it has a bad sensor causing the problem, but this also has no diagnostic port that I’m aware of, and the under the hood ‘code reader’ that has a pin and blinking lights says that there are no codes. This has the Bosch injection system (I guess some have different fuel injection systems). Please help...
 

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I'm having almost the exact same situation, but it is not with a Volvo. The symptoms, however, are exactly the same. Does your car, by any chance, not want to start back up after it is warmed up/fully hot?

when I start it and warm it up it runs like it should. But after it’s hot and been driven around it will pulse at idle from 750-500. it will be at 750 And it sounds like the engine is about to die until it hits 500, then the engine picks up again to 750, and starts to die again, it happens rapidly.. the other part is that when your driving and you accelerate hard enough to get into the boost, then slam on the breaks the car will die. It does not happen if your cruising and slam on the breaks, and it does not happen when you break for corners or slow down moderately. It’s only when the boost is high then the breaks are slammed. It also dies when your in drive creeping forward without any giving any throttle and turn. It seems to me like the power steering pump is putting more strain on the engine that is idling bad to begin with. All this happens with the A/C pump on or off...
The car that is doing the same things with me is not only not a Volvo, but not a Turbo. However, I believe the answer is almost the same, in the similarity of symptoms...

I started with a new battery, spark plugs, and wires. Nothing changed.
You replaced everything that the spark travels through, and gave it a good tune-up.

Your issue is probably with the source of the spark, and perhaps somewhere in a failed distribitor, rotor, or, more than likely, for the win.. an ignition coil putting out weak spark to the engine and failing under severe load, in the case of this car Turbo Boost, or sometimes failing to provide enough current when hot, as the power output goes down.

It's either that, or a fuel delivery problem.

Good compression?
Your car almost certainly has a distributor, on a 1992 Volvo 8-valve.. Yes
Fuel is being delivered good? Starts up fine, so, it must be.. failing fuel pump will affect starting..

I'm going to vote for weak spark
Please pull a spark plug wire off, read how to make the spark jump safely to a tool like a screwdriver, and please post back and tell is if the spark is yellow, orange, or white/blue. You will notice that the white/blue spark jumps considerably longer than the weaker yellow and orange spark, and please don't be holding the screwdriver when you do this, just have it laid on the top of the engine and either try to view it through the opening of the hood up, remote start the car with a relay tool that functions as the key, or have an assistant look for spark. using a video has to be put in perfect view, as it can be hard to see.. This if you are doing this 100% by yourself.

I'm voting weak spark.
 

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Discussion Starter · #3 ·
It has a new fuel pump and filter, I forgot to add that originally. And I will check the spark, thanks for the reply! I’ll let you know how it goes
 
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