Hello,

I've been having an ongoing fuel pressure problem that I can't seem to figure out and would greatly appreciate some advice on.

My problem is that my car hardly starts with the vacuum line attached to the fuel regulator and works just a little better with the line disconnected. It will only run for about a minute or less before stalling out.

My car is a 1988 Volvo 240 sedan and has never run quite right in all of the years that we've owned it. It had a fuel pump failure (which was fixed) but also has several other problems that may or may not be related. All of the current problems seem (to me) like they might be linked so I'm hoping that someone might be able to make sense of them.

The car seemed like it was starving for fuel. I checked the return gas flow out of the regulator and it seems strong. I've replaced the fuel regulator twice. Once with what I thought was a working used one and also with a new one. Also a while back with a possibly incorrect one.

I don't understand why disconnecting the vacuum line helps the car run better - it seems like the opposite should occur. I would think that reducing the vacuum would send more gas to the engine?

The engine almost always dies immediately if I try to give it any throttle.

My MAF sensor also seems to be bad. I have it disconnected. Runs worse when connected. Not sure if this is related or not.

When the car starts it runs smoothly and then just slightly sputters and dies with no missing beforehand.

Thank you in advance for any advice. I would greatly appreciate any help.

Regards,
Tim

 

did you pull a spark plug to see if fouled/running too rich?

 

Thank you for the suggestion silvermine. I pulled a plug this morning and it had a lot of carbon on it. I put new plugs in a while back and they couldn't have more than an hours worth of runtime (probably a lot less). I guess that this indicates too much fuel?
.
The car occasionally seems to run longer now. Sometimes it runs for over a minute before it dies. If you try to start it immediately after it stops, it won't start. If you wait a minute or two it will start again.

When running the engine sounds great and purrs right along. If you give it the least amount of throttle it dies immediately.

Thank you again.
Regards,
Tim

 

you said you could only get it running with the MAF unplugged?

if so, you have a bad MAF.

 

seems like it's running rich...
before replacing, you could try cleaning your MAF with proper MAF cleaner and then plug back in and see if that
helps.
does the vacuum line from the FPR smell of gas?

 

Does this engine have the water temp sensor for cold start. If so this may be an area to look at also. Also the IAC

 

I've never had MAF cleaning do any good, when I've inspected the MAF's they've always been quite clean inside. I suppose if you had a defective air filter, or your engine backfired quite a bit, they coudl get sooted up.... if you do this, hold the MAF so the electronics module and connector are on the top side, with one end tilted slightly down, and spray from the higher end, this way the spray won't run down inside the electronics module.

 

they all have a coolant temp sensor... if the IAC is defective, it still should start if you hold the gas pedal sligthly depressed when you start it. cracked IAC hoses would tend to cause it to run too lean (due to too much air) whereas the symptoms seem to be too rich.

 

Thank you for all of the valuable suggestions Silvermine, Pierce and Jagtoes. I really appreciate the help.
I’ve definitely been at a loss for quite a while but feel like I have a chance of making progress thanks to all of your suggestions.

Things have changed somewhat with the car. I’ve been starting it off and on while working on other things and it seems to run a little better each time I let it run (No idea why). It’s to the point now where it will start up and idle smoothly and indefinitely after four or five starts.

The car usually stalls or runs poorly when any throttle is applied no matter how long it runs.

Here are the current symptoms:

1.) Hard to keep idling for the first several starts. (The car always fires with only a crank or two and starts right away after sitting for about a minute or less after it stalls.)
2.) Wont start easily or run for very long when the vacuum line is hooked up to the fuel regulator.(Things seem to have changed with this a little – the engine will idle just fine with the vacuum line attached as long as the engine is at operating temp.
3.) Giving the engine any throttle at all almost always results in an immediate stall. Sometimes giving throttle causes the engine to slow down and miss like it is starving for fuel. Very rarely the engine will rev up almost perfectly.
4.) When the engine doesn’t stall while depressing the accelerator, and the rpms slow down a low, throaty idle sound will come from the air cleaner box.
5.) When at idle the car sounds great. Quiet, no misses, no sputtering. Just perfect.

So at this point the MAF is not working and is disconnected. The Vacuum line is disconnected from the fuel regulator and the car idles well for the most part. It seems like it would idle forever but just won’t rev up properly. Yesterday at least, it seemed like the vacuum line could be hooked up after the engine warmed up to operating temp - still wouldn't allow any throttle though.

The vacuum line that hooks to the regulator is just hanging open and sucking air. It seems that if I attempt to block it the engine runs slightly slower.


I hate to add any thoughts because I’m at a loss (and am probably wrong) but it seems to me that the car stalls because it isn’t getting enough fuel. Could the fouled spark plugs be caused from all of the failed starting and sputtering before it started working better?

I really appreciate all of the comments. I’m looking in to each of them. I apologize for not replying sooner. I spent a long time replying yesterday and when I went to submit the reply my session had timed out - I lost it all.

Thank you again for all of the replies. I really appreciate the help.

Regards,
Tim

 

With the MAF disconnected, its running in 'limp home mode'. YOU NEED A NEW MAF.

 

you're probably right pierce but he could try cleaning the MAF first, they're on the pricey side...never know might work...

 

I do agree with you pierce. I do intend to either change out (or more hopefully) manage to clean the MAF.

Would anyone be able to tell me if the limp mode would be so severe? The car still won't run with the vacuum line attached until the engine is at operating temperature and, more importantly, the car won't move at all (stalls) because it doesn't have enough power if you put it in gear. If this is limp mode I wouldn't be able to limp in inch.

I have another Volvo that hopefully won't end up being a parts car that I can borrow the MAF from. I really hope that I can resurrect the one that isn't working though.

I'm pretty sure that the MAF was working when these problems started....It's been so long that I can't remember. I do know that the car has backfired through the air cleaner several times during the times that I've messed with it in the past.

My plan for the next step is to get the MAF working. Thank you for the advice.

I would have replied sooner but the rain and flooding that we've been getting here is absolutely killing me. I need to get this car somewhere where the weather doesn't keep me from working on the car.

Thanks again!

Regards,
Tim

 

LH injection, the primary input is the MAF, this tells the system how much air is going into the engine, so it knows how much fuel to inject.

without the MAF, it only knows 2 things, the throttle is not at idle, and what the RPM is, so it has to GUESS how much fuel to inject, and it has to err on the rich side as a too lean motor burns holes in pistons. it will have very poor throttle response, and no power, basically barely run and only at lower speeds.

 

Well, I had some success and a major disappointment this morning.

I tried cleaning my old MAF to no avail. There was no change. I then installed a MAF that I borrowed from another working car and although the car didn't run right, it did run better. Thank you all for the advice with this. It was good to see progress.

The disappointment came about when the original problem that this car suffers popped up again....The car lost all spark.

Extremely intermittent spark was what made me park this car a couple of years ago. I had been troubleshooting this problem off and on and finally let the car sit for most of a winter and summer. The fuel problem started after the car had been sitting for so long.

I suspect that the intermittent spark problem is the hall effect sensor. I never had a chance to verify because the car suddenly started running again without another failure.

I guess that I'm going to have to start over from scratch - I lost my notes from troubleshooting the sensor, coil, and distributor.

All I know right now is that the tach doesn't seem to be getting any impulse (the needle is dead) and that I have no spark from the coil.

Obviously, I won't be moving forward with the fuel problem for a while. It might even be fixed.
Thanks for everyone's help! You're great.

The car only ran for a couple of cold starts with stalls when the spark died. It was looking very promising and I was thinking that the car would run much better once it warmed up. That's when the engine shut off. Didn't get a chance to warm up even a little.

I might end up starting a new thread after I do some research on the hall effect sensor. Last year I was getting ready to hook up an oscilloscope to see if I could find a 5 volt signal from the sensor. I got too busy and had to abandon working on the car and now I've forgotten almost everything that I had learned. I do know that I wasn't making much progress because my wire colors didn't seem to match any troubleshooting guides that I found.

Thank you again.
Regards,
Tim

 

the signal from the hall sensor is farily low level and has to be amplified by the ignition control unit, there's a DC bias voltage across the wires. the most common failure I've seen is in the thin pair wires that go to it, where they go through the side of the distributor.