Occasional loss of power.

[AllHailKingVolvo]

Fitting a new underbody fuel pump has made a big difference to my 744, loads more power and smoother under acceleration. It was prone to stumbling and hesitant periods before changing the pump. I’d definitely investigate it...if the brushes and/or commutator in the pump are worn and occasionally breaking connection, it could be the case that the car is experiencing fuel starvation for short periods hence the hesitation.

Mine was generally okay starting wise, but is a lot better now.

[Laird Scooby]

I wonder if the starting will be improved with the 4-pintle injectors?

[AllHailKingVolvo]

Originally Posted by Laird Scooby

I wonder if the starting will be improved with the 4-pintle injectors?

It is better...Right on the button now!

[Delta66]

It happened today, this time I was only doing about 10mph having just turned into a side road and the engine died completely, the rev counter going to zero as the revs dropped. It took about 4/5 seconds from feeling the loss of power to the engine cutting out. I turned the ignition off completely, waited 5 seconds and it started first time and has been running fine since.

Is that still suggesting the fuel pump?

[Laird Scooby]

Did the rev counter drop to zero as soon as you felt the power loss or only after the revs had died completely?

[Delta66]

Only after the revs had died completely.

[Laird Scooby]

If the rev counter was still registering something until the engine physically stopped turning then it's fair to say the CPS is probably ok.

This is a bit of a hunch based on a recent bit of experience but worth a try.



First, check the relay in position "E" as shown on the diagram is pushed fully home.

Second, renew fuse #1 with the correct rated fuse. Don't just pull it out and think "yeah it looks ok" as they have a nasty habit of concealing hairline breaks that only appear when the fuse gets warm after some use.

See if that improves matters.

[Delta66]

Done. The relay did not move, so I presume it was seated fine and it is the same as the others I can reach. Fuse 1 looked fine but swapped (with the horn which still works OK) as I don't have a spare.

[Laird Scooby]

Originally Posted by Delta66

Done. The relay did not move, so I presume it was seated fine and it is the same as the others I can reach. Fuse 1 looked fine but swapped (with the horn which still works OK) as I don't have a spare.

The horn, by its very nature is only ever used intermittently so it's doubtful a hairline fracture in the fuse would ever show up. Chances are it's probably ok but if it does cut out again, please fit a new fuse to eliminate that from the fault finding process. It's not like they're expensive :

https://www.ebay.co.uk/itm/CADILLAC-...Y/113027602134

Less than £1.20 delivered - a cup of coffee in McDonalds is more i'm sure!

Glad the relay itself was seated firmly in its home, i know of a 940 recently that was reluctant to start and would occasionally cut out or "fluff" a bit while driving. The owner sent me a photo of the fuse box in connection with something else and i spotted the fuel pump relay was sitting skew-whiff. He pushed it fully home and problem solved!

You can't quite see it in this photo but the overdrive relay (square green - the round green is the bulb failure) on the right was the one i noticed in this pic, can't find the other pic from a different angle where the fuel pump relay (on the left, white one) also appeared "not quite right" but it seems someone at some point had several relays out and didn't put them back right.

Going back to the fuse, i can't count how many faults i've fixed where the fuse has been the culprit with a hairline crack that only ever shows up under load because it gets warm - usually by the time you get the fusebox cover off and so on, it's cooled down enough so the crack doesn't show.

If it seems i'm going on about it a bit - that's why!

[Delta66]

Update on progress. Got a code reader and the only code to appear was for the mass airflow sensor. Since it was a cheap ebay one I fitted some time ago dealing with lumpy running and uneven idle, I decided to use the Euro Carparts next to my work and get a HAAS one, which got for £99.

I cleared the ECU and fault codes, fitted the new sensor, started the car, ran it for a short while and then checked the codes again, all was fine.

I took the car for a drive and went via the dump with a load of rubbish. All fine.

I then started the car, the engine started fine, there was the normal woosh as the revs blip above 1000 and then it cut out. It took another 5 attempts before the car would start and then it was fine again, as if nothing had ever been wrong. Got it home, checked the codes and AGAIN the only code was the airflow sensor!

It is now booked into the local garage, but on explaining the problem the owner admitted he was a bit stumped.