Rough running after fuel pump replacement

Craigd2599 · Post by **Craigd2599** » 25 Jul 2018, 14:14

1997 850 2.4 NA changed fuel pump yesterday. Car started rough but smoothed out immediately. Drove it around the block ran like a champ. Daughter tried driving it today, starts rough again. Too rough for her to try driving it. (I'm not home at the moment)
Any thoughts?

Post by **abscate** » 25 Jul 2018, 14:39

You need to sort out if its on the ignition or fuel side of the troubleshooting tree.

Fuel pressure at rail is the solid test for delivery - usually nothing goes wrong after that.

How old are coil, cap rotor, wires, plugs?

Craigd2599 · Post by **Craigd2599** » 25 Jul 2018, 14:41

It's time for a tune up but the thing ran like a Singer sewing machine before the pump failed

Post by **tryingbe** » 25 Jul 2018, 14:48

Here's the thing; everything works until they don't.

So, instead of insist something worked great... verify what works and what doesn't. People on the internet can't troubleshoot a nd diagnosis without information, you can get the information by measure the fuel pressure at the fuel rail, do compression test, check spark plug wires, spark plugs, check compression numbers, and etc. If you can't do the work or don't want to, send it to a shop.

Craigd2599 · Post by **Craigd2599** » 25 Jul 2018, 15:57

So...
I've worked on more than my share of Volvos, Chief. I went through the checklist when I diagnosed the fuel pump in the first place, which is why I'm asking here.
Maybe you haven't posted in a while, but this place is normally very friendly.
People here are helpful...not smug.
Thanks anyway

Craigd2599 · Post by **Craigd2599** » 25 Jul 2018, 15:58

abscate wrote: ↑25 Jul 2018, 14:39 You need to sort out if its on the ignition or fuel side of the troubleshooting tree.

Fuel pressure at rail is the solid test for delivery - usually nothing goes wrong after that.

How old are coil, cap rotor, wires, plugs?

As soon as I got home and started the car, it ran perfectly. I'm thinking it had some air in the lines after the pump changeout. Ran it about five miles and it was flawless.
Thanks for your input!

Post by **abscate** » 25 Jul 2018, 16:25

I had quite a bit of cranking and sputtering on my 99 after the PCV job, where I had broken the fuel line and lost pressure. I suspect you are right on that diagnosis.

Craigd2599 · Post by **Craigd2599** » 25 Jul 2018, 16:27

Thank you! I'm driving it to work tomorrow (It's actually my daughter's car now) if it starts rough in the morning, I'll throw the pressure gauge back on it and see if it's leaking down. In which case I'll swap out the regulator. But I think we're okay.
Thanks again for your input!

Post by **JimBee** » 25 Jul 2018, 17:35

You haven't mentioned the brand of fuel pump you installed. If it's a Walbro, and you can't figure out what's causing the roughness, try pulling the pump, removing the filter and reinstalling it just to try it. The Walbro I bought wouldn't start my 850 at all. Finally discovered the sock filter that shipped with it was for E85 fuel and for some reason I still don't understand, it wouldn't pass through enough gasoline to start the car. With the filter removed it started and ran fine. The vendor finally sorted it out and sent me the right filter.

The wrong one has a rectangular pattern of small holes, maybe 1 mm diameter. The right one is a fine mesh with no distinctive holes. They're visibly different.

Craigd2599 · Post by **Craigd2599** » 25 Jul 2018, 17:37

This one had the fine mesh. I matched it with the old one before installing. It was an Airtex.