1998 V70 - Engine Runs Rough After Sitting (ECU replace,ent) Topic is solved

[whirligig]

Make sure you check the battery cable to the starter -- in particular, the ground that bolts to the front subframe cross-member. I had a cable corroded completely through there and the cable appeared intact until you went and tugged on it. This can cause intermittent starting/stalling issues that can take quite a while to diagnose.

There is no issue with the starter. It cranks after a stall. I'm not getting any ignition. I'm not sure if it's starved for fuel, flooded, or no ignition.

What's the status of the ignition parts on this car...plugs wires cap rotor coil? How old are they?

The cap, plugs, and wires were recently changed at 180k. They were new when I installed them at 120k. I made the mistake of having my mechanic complete the 120k service and he removed everything I did and installed new stuff over my lightly used stuff. I kept the parts since they only had a couple of hundred miles on them. Several years later, I brought them out, cleaned them, and re-used them. They are working fine. I went on 150 mile round trip to Santa Paula last weekend and not even a hiccup. Then I let the car sit a couple of days and it starts kicking me in the ass and quits a mile out of the starting gate.

I just ran my homemade smoke machine and found a minor leak in vacuum hose at the purge control valve. That's replaced. There's no smoke or leaks toward the rear of the car but I did patched small crack on one of the J-hoses. This Uro hose is only a couple years old and it has a crack. Anyway, I'm starting to think it might be the EVAP system. Possibly a clogged charcoal canister or a malfunctioning valve. Maybe the mechanic can tell me.....

[whirligig]

My mechanic's diagnosis is the ECU is not working right. He saw engine hesitation. The ECU has been replaced. He told me that I would never have found it and he's probably right. We'll see if there's any issue when I have a chance to let the car sit for a day or so. So far the car is running fine.

[erikv11]

A bad ECU is pretty much unheard of. Good job by your mechanic if that is the case.

[whirligig]

Morticia is fixed! I started the car this afternoon after she sat undriven Sunday about 40 hours. It started with no problem. I drove it around town taking care of errands. It ran just fine with no hesitation or stalling. So this is a wrap. It was the ECU.

A bad ECU is pretty much unheard of. Good job by your mechanic if that is the case.

My mechanic said it was also quite rare. However, he did show me a cabinet full of ECUs that he used for troubleshooting. Like any piece of electronic that has to work under extreme environments such as heat, cold, vibration, emf, etc. It may face fatique, component failure, and cold solder joints. I wish I had a chance to inspect my old ECU but it was needed in a swap for its replacement. Anyway, its done now. Thanks everyone for your help.

[abscate]

This past month I replaced a myriad of fuel related items on my 1998 V70 with over 180K miles. The fuel pump relay/controller failed and it was replaced with a Kaehler unit. Sometime later the fuel filter was replaced with a new Bosch because it was due. After this, I encountered rough running sometimes stalling if the car sits for more than one day. Subsequent starts for that day, the car will run fine like nothing happened. I then checked the fuel pump.

I conducted three pressure tests on the old fuel pump. The priming (i.e. turn the ignition key 3 times without starting) came out about 40 psi. The running pressure was 45 psi. But the fuel leak down test was showing a pressure loss from 38 psi to 27 psi in 36 minutes. So I replaced the old fuel pump with a Hella unit. It runs fine for the most part but I'm encountering the same stalling and rough running if the car sits for more than a day. I get an occasional stumble if it sits for 12 hours. I get stalling and rough running if it sits for more than a day. I have not done a leakdown test since installing the new pump but I suspect a leak somewhere. I just can't find it or smell it (yet). Is the rough running due to air in the lines? Could it be a leak around the injectors? Would a check valve work? Any clue?

By the way, this fuel system does not have a return line nor a pressure regulator.

Rare case of ECU replacement. Of course: without root cause and a third party, this is not a clean diagnosis.

[whirligig]

Boy, this was painful re-reading this stuff again. Yes, I suspect I could have still used my old ECU. The reason I say that is the new MAF sensor at the time became defective after just a year. OBD data showed abrupt air flow changes at idle. After replacing this with an old one, that problem went away. I haven't had a start or stalling issue since if I exclude the pre-mature timing belt failure at 187k but that's another story.