'99 S70 AWD w/ new fuel pump - surging

[DurangoStang]

I recently replaced the fuel pump on my '99 AWD S70 using the floor cut technique, and I'm still having trouble with the car surging upon start-up (revs to about 2000 rpm, then back down to about 800 in 1 approximately 1 second cycles), and "sputtering" for a few miles/minutes (like it running on 4 cylinders, even after the surging has stopped). I replaced only the insert (I found a Walbro GJ 235 from a place in England - more on that in another post), and I'm wondering if I put the assembly back together correctly? My theory is that something isn't sealing correctly, thus allowing the system's pressure to dissipate after the car has been off for a few minutes. At the base of the Walbro insert, at the intake tube, there is a blue rubber "doughnut" that fits into a recess at the bottom of the housing. Does this need to seal to to anything? Below this, there is a plastic screen, and under that is an orange piece of rubber (that is, if I have this together correctly). This appears to be a check valve. The orange piece is loose below the screen - it can actually rattle around if you shake the assembly. As far as I can tell, this is correctly assembled, but if someone knows differently, or has some suggestions of things to look for, I'd appreciate your insight. Also, I'm wondering if the seal below the ring where the fuel pump mounts inside the gas tank could be leaking and causing this problem. I had trouble getting it to seal, but think I have it good now (a little finessing was required to get the "lip" around the seal to go around the neck of the tank without being folded under). I did press the valve at the end of the fuel rail tonight after the car had been sitting for a few hours, and nothing came out. Finally, there is the possibility that this is a completely new and unrelated problem. Again, any insight into how to fix this would be appreciated (and yes, I'll buy a new assembly if that is what it takes, but would prefer to just fix what I have - partly a $ issue, and now, partly pride!). Thanks in advance.

[rspi]

Did you check fuel pressure? Also, my guess would be a bad IAC valve. Do you have a CEL?

[DurangoStang]

There is no pressure when the car is off. I didn't check it when running. There is no CEL. After reading some other threads last night, I'm leaning towards a bad check valve in the fuel pump assembly. Thanks for the input - I'll look into the IAC valve.

[misha]

Did you have those symptoms before you replaced fuel pump?

[misha]

There is no pressure when the car is off.

Fuel pressure should be performed like this:
Turn the key into pos II(do not start the car) and check for a fuel pressure at fuel rail valve
-you should have a nice squirt of fuel from that valve
If not...fuel pump or it's relay are dead(this is not your case because your car starts & runs)

Next....you should check for a fuel pressure when car is running.You should have 43.5(on first prime without starting the car & on full throttle at high rpm's).At idle you should have around 30-35 psi.

[DurangoStang]

The car didn't have surging problem until I replace the fuel pump. I'll check the fuel pressure as you have described, though.

[misha]

The car didn't have surging problem until I replace the fuel pump.

Then...your problem is a bad new fuel pump or a bad installation of a new fuel pump.I suggest to go back and to check everything related of the replacement process.

[DurangoStang]

Misha - thanks again for your input. I actually replaced the Walbro insert only, and re-used the rest of the fuel pump assembly. I think the check valve built into the assembly is not working correctly, or the "blue doughnut" seal at the base of the insert is not sealing correctly. I can take the fuel pump out and disassemble it fairly quickly, so I can look at these parts fairly easily, so any advice on what to look for inside the assembly (all the parts, how they go together, what to look for, how to tell which one is not working, etc.) would be appreciated. A diagram of the assembly would be really helpful too.

Another theory is that the Walbro insert is bad, however, it is actually the second one I've tried. The first one was missing a small metal cap at the top of the discharge tube, but I tried it anyway. Without that cap, I assumed that there was a leak at the discharge tube (which maybe there was), but both have the same symptoms.

[misha]

As far as i heard...AWDs have a different fuel pumps & housings than FWD Volvos(not 100% sure on this,but that's what i heard).One thing is for sure....all pre '99 FWD models have built-in check valve in their fuel pumps not at the assemblies.

Anyway,i have this Walbro fuel pump replacement procedure,maybe it will be helpfull:

Walbro fuel pump replacement.zip

(4 MiB) Downloaded 189 times

[DurangoStang]

Misha,

Thanks for sending that. Unfortunately, yes, the AWD is a fairly different setup. There is a thread on this site that goes through how to take the pump out of the tank by cutting a hole in the car's floor (the pump is mounted on the front of the tank on the AWD models), and replacing the insert, however, the photos only show the top of the pump insert, and not how anything goes together at the bottom of the assembly, including the check valve. The check valve on AWD models is part of the plastic housing between the intake filter and the insert. It's a very simple design - just a thin piece of rubber that sits inside a small chamber. I can suck and blow on the filter side of this, and it seams to work correctly, but once installed, the car still surges and runs bad for 5 minutes or more, then it's OK after that, indicating that the insert and other valves are probably OK. I need to find instructions and/or photos like the ones you posted for AWD models. Maybe if I get motivated, I'll pull the pump again and take some photos. Maybe I'll try some of the other web sites, and/or buy a used one on eBay. Thanks again.

https://www.matthewsvolvosite.com/forums ... =1&t=20367