Hi all, I am going to take a stab at this. I've been searching through the forum and have found a few issues that seem similar to mine, but want to write it out in case something jumps out to all of you.

So, my problem is that the car, seemingly at random, will lose power and the engine will die. I've been trying to detect a pattern, but no luck so far. Most of the time it runs great. When the problem occurs, the car won't immediately start up. You have to wait for 30 or so minutes. Because of this I thought it might be limited to when the car is warmed up, but it happened to my wife just driving a few minutes from the house.

I took the car to the local Swedish specialist in my area and they were able to reproduce the problem during a test drive. Great! Right? Not so fast. They ran diagnostics and asked me a bunch of questions, but in the end they said they couldn't figure it out and threw in the towel. I don't want to give up just yet. The car is pushing 300K miles, but is a workhorse and basically runs great still (and I just recently bought new tires, ha). The way the car loses power reminds me of the problems I had when I had to get the MAF sensor replaced three years ago, but the mechanic said he didn't think that was the problem this time.

There is another mechanic (not a Volvo specialist, but he's good at older cars) I am going to take the car to when they reopen in mid August, and I am wondering if there are specific things I should point out as possibilities, especially since I can't be certain the problem will reproduce during his test drives. Looking through threads on this forum, the likely culprits are:

- vacuum leak
- wiring harness connections
- crank position sensor
- fuel pump

If the wisdom of the group can offer some advice, that would be great.

Quick disclaimer: I love driving my Volvos (had an '83 wagon before, have been driving my '92 since I bought it from the original owners in 2010), but I don't do the wrenching myself and am afraid I may not be useful when it comes to answering specific questions or providing technical information.

 

I'd bet on the fuel pump or fuel pump relay. I suspect that as you drive the pump heats up, draws too much current and the relay temporary fails. you stall, things cool off a bit and off you go. Have your shop test for the fuel pump current draw. You can also try dropping in a new fuel pump relay - but usually when the relays go, its an early warning the pump is about to fail.

 

Have you checked your noise suppression relay? A black rectangular relay under the hood - they fail like the white fuel pump relays do, cracks in the solder joints on the circuit boards. I've replaced hundred over the years for cracked solder joints and poor/no /stall running conditions.

https://www.matthewsvolvosite.com/fo...ic.php?t=49080

https://www.partsgeek.com/gbproducts...hoCWDEQAvD_BwE

 

Crankshaft pos. sensor number one suspect, fuel relay distant second.

 

+1 on the crank position sensor. Check it for cracked and flaking insulation. That is a sure sign it needs replacing.

 

It can look healthy yet be bad, can look flaky, yet work, seen both types...

 

Good leads given so far. But you may want to check into your cpu!!! Immediately

Goldenblock

 

Mt6127, this sounds like a good tip. It's funny how the car usually gets along fine without a problem. Would the fuel pump cause the engine to stall only sometimes and not all the time if it isn't drawing properly?

 

Hi there hoonk, will check on this ASAP.

 

Hi lev, act1292, and Goldenblock, great tips, thank you! I'll see what I can do. I don't normally do a lot of fiddling with the engine, so you've given me some homework. I'll do my best, and at the very least I'll have some good suggestions for the mechanic when I take the car in to the shop in a few weeks.

Really appreciate the help, fellas.

 

Hi Hoonk, and All. I have a similar problem. My car will run for 7 hours straight on a road trip but if the ambient temp gets above 90 outside the car starts to miss fire and eventually shuts down. I was told by a Volvo expert "so to speak" to try the Fuel Injection Resistor Unit (located behind the driver headlight) as next "throw parts at the problem" solution. I have not replaced the fuel relay under radio. but have done the cam position sensor, fuel pump and so that something needs to be next try solution. Do you know a good brand to get on the fuel relay--they seem to vary from $12 to 70 dollars. Should I try the "relay" first or the "resistor" first?

Also what does the noise suppression relay have to do with the fuel? and where is that located exactly?

 

I've never heard of the injector ballast resistor (a turbo only feature) failing.

 

I've never seen a bad resister, (the 4 wire wound thingy with a white connector), but have seen bad/melted connections at them.

I did not have the luxury of "trying" parts to fix my customers cars. I had to prove things were bad, If I didn't and put something on that did not fix their problem - I would lose them as a customer and they would tell 10 of their friends how i ripped them off......

So - Not knowing what year your car is - if you've got the black self diagnostic box you can plug the free wire into - (engine has a speed sensor and there are no electronics inside the distributor) plug it into #2 and check for self diagnostic codes. (then find a code book/legend to tell you what they mean) If there is a flywheel speed sensor, check it's resistance, if the black insulation is falling off of it - or the resistance is out of spec - replace the sensor.

Remove the white fuel relay, take the lighter tray out, 2 screws originally, 1 now to get to it, pry the cover off, note the date of manufacture on it, it is really old? (replace it) With a magnifying glass, examine the solder joints on the circuit board where the electromagnet coil wires are soldered - that's where the joints crack. Visible as a little fuzzy line all the way around the joint. replace or re-solder them. Find the Noise suppression relay under the hood, maybe in the rf corner of car buried under a wire harness (it's been a few years), You can tell if it's the right relay by - unplugging it while the car is running and - the engine stops running! That relay powers the fuel injectors. Pry the cover off, note the date of manufacture on the outside. Examine and find the cracked solder joints - try to re-solder them or replace the relay. I tried to always use the Factory brand of relay, but don't know if they are still available. Some cars have 2 of those black relays under the hood, 1 is for the aux cooling fan (could be a 240), if so you can swap them to test with.

Just reread your post - a 4 cyl does not have a cam position sensor, and does not need one, only the 5 and 6 cyl. need one to start. I can only guess you are referring to the engine speed sensor on the flywheel.

And you are a brave person to drive a very old car 7 hours!

 

Also you replaced the fuel pump, the one under the car or the one in the gas tank?

 

Goldenblock here again. Thanks for the shoutout. Based upon my knowledge i dont believe its cps, or rsr or fuel pump current. All possible but not likely.
please take a visual inspection of your computer, wiring etc i believe thsts the senior issue if its running fine for 30 plus.

I have a regina 2 pump system and had a similar experience.
So diag cpu immediately.

I have over 2 million miles( no misprint) on my 740 so ive seen it all.

Goldenblock

 

ECU's rarely go bad - except for the "pink label" ECU which was used on the LH 2.4 systems between '89 and '90. The pink label ECUs have a pink label on them (thus the name). Post '90 ECUs have a white label and rarely fail but is not totally unheard of. The pink label ones have a weak circuit that drives the fuel pump relay that fails over time. If you have the pink label ECU, you might want to scout the junkyards for a white label replacement. A search of the forums here will give you exact part numbers.

On the other hand, crank position sensors and fuel pump relays (and radio suppression relays on the 740s) are wear items - meaning they will wear out earlier. That's why I would start there

 

theres a table here of which ECU's are compatible.
https://www.volvoclub.org.uk/faq/EngineFIComputer.html

 

Hi all, wanted to give a quick update. The mechanic found that the fuel pump relay was in rough shape. It was original, which he found very surprising (manufactured in Germany in 1991 for my 1992 940 Wagon)... he figures there are probably very few original parts like that out there so old, especially for a car with 300K miles. Under the magnifying glass he could see that the contacts were messed up.

So far the problem with losing power hasn't happened in the week I've had the car back. Would be great if that did the trick. If it happens again, at least I know what's NOT the problem.

Will post an update later if there is one worth making. Hopefully you won't hear from me too soon!