I have a 2001 Volvo S80, for the past 2 months i have encountered a loping issue when i start the vehicle. It is very random. Some days it does it and others it does not. When it is loping I can’t get it to rev over 2,500 RPM. I put some sea foam in the fuel tank and it ran for 3 weeks with no issues, but now it is back to loping again. If i rev it up and hold 2000 RPM it takes about 20 minutes before it cleans out and runs normally. I have put a fuel pressure gauge on it to see what it it is doing while loping. It holds 58 PSI and drops down to 56 when loping but when it drops down all of my electronics go dim so i assume that the fuel pump is losing power as well during this. I removed the Mas air flow sensor and cleaned it out and re installed, no change there. I have also removed the ETM and cleaned it up as i have read that it can build up carbon and stick. My ETM was not that dirty but did have some carbon built up on it. I reinstalled it and still no change. I have run 2 tanks of fuel through it with sea foam, since it worked before but not this time. I am also getting more symptoms. I was driving on my way home from work 4 days ago, i was doing 70 MPH and then my engine RPM dropped down to idle, 1,000 RPM. I had no throttle response in the gas peddle. I pulled off the side of the road and pushed the peddle to the floor and back up numerous times. Then bam working again, got back on the road and it did it again. It did this. 4 times on my way home from work, I have a 20 minute commute. I’m not getting any check engine lights but I hooked up a scan tool to see if it was throwing any codes and it is not throwing any. i2 days ago, I drove it to work and when I went to leave I turned the motor over, it Hits 1000 RPM and then dies. I am taking my Truck and trailer to work and picking it up to bring it back home. I feel like the next thing is throwing parts at it but this is a terrible way to fix a car.

Any Suggestions welcome.

 

Nice

 

Sounds like you have a fuel delivery issue. Could be the fuel pressure sensor/regulator, could be the fuel pump or the fuel pump relay (note that a failing relay is a sign that the pump is failing and drawing too much current). Could also be something like a throttle position sensor - tough to diagnose when there are no codes. Try jumpering the relay to see if that helps the car to start.

 

I agree. Some type of fuel delivery issue seems most likely. Have you checked fuel pressure? Might be best to take it to a shop for propper diagnosis rather that continuing to throw parts at it.

 

I think (that's always trouble) that the lights dimming and voltage drop are more a symptom of the root cause , and the fuel problem is just another symptom. Low voltage is going to cause both the pump and pressure sensor to malfunction. I believe the sensor failing causes a rich mixture (so as to not cause engine damage and not strand you (like Volvo cares about that!). But the phrase " takes about 20 minutes before it cleans out and runs normally" sounds like it's running rich if you mean that it takes a while to clean out excess fuel. Your pump may be failing and drawing extra current, Filthy fuel filter? I doubt that as I can't see it coming and going.
Who knows what the Seafoam is knocking loose. Crud clogging the pump would possibly make it pump harder/longer. But I can't see how that would make it eat current.


You may have an intermittent short and since it is presently not starting the short may have progressed to a permanent short which is much, much easier to locate.
I would first get in there w/ a multimeter and look for trouble then go after the pump and sensor. (and the filter if it's original).

And finally, using solvents as strong as Seafoam is nor without risk on an old engine.

 

Alright, so I decided to start with the basics and go with a tune up. I replaced the fuel filter and then I decided to replace the spark plugs. I pulled all the spark plugs and the plugs in cylinder #4 and #6 were caked with oil. Obviously these are not firing. Weird I would not get a miss fire code. I pulled the coil out of #6 and started the motor, it is still loping the same. I have ordered 2 OEM Bosch Ignition coils from Amazon, my local parts store wanted 160.00 for one coil that was a Duralast brand. Bought the OEM ones for $44.00 a piece. I’ll put these on and see if it fixes my issue.

 

So it was not starting because it was In limp mode some Fail safe Mode. I disconnected the battery for 20 miniutes and plugged it back in. Fired right up but still loping. I pulled the spark plugs out to replace them, the number four and the number six cylinder plugs were caked with oil. I did some troubleshooting with coils it seems like they are not even firing on four and six I bought two brand new coils off Amazon they are the OEM ones put those in and it’s still loping. I unplugged the new #6 coil while it was running and no change in motor RPM or loping. If i unplug #1 it changes drastically. Maybe injector?????? It smells like gas when it is running for 5 min so that tells me it’s getting fuel just not burning it. Sorry I’m also just spit balling here too.

 

Oil or gas?
Oil would indicate bad rings (check compression but I would not suspect that first) or bad valve seals which pop up on engines driven w/o oil for a while.
Can you get some spark off those 2 cylinders at all?

 

I’m getting spark on all 6 cylinders. I did a compression check on the cylinders. 135-140 psi on all cylinders then i added a little oil to all cylinders then did it again jumped up to 180 on all except 4. Number 4 jumped up to 300.
just not sure on the gauge i am using because I feel like i can’t get a good seal on it due to its 6” down a hole.