98 V70 GLT Misfire and bad gas mileage

MoparWade · Post by **MoparWade** » 22 Dec 2013, 20:58

Took a trip in my V70 today and I noticed initially that my fuel economy was down but attributed it to having a bunch of stuff in the car. However, later in the trip I encountered an idiot who just wouldn't get out of the way so I punched it and passed. When I did everything was fine at lower boost but once up at 12 I could feel a misfire and sure enough I got a code for misfire in cylinder 4. Have had some minor surge issues in the recent past but it only happened a couple of times and ony at freeway speeds and it was just a little stumble. I did the full IPD tune up with cap, rotor, plugs and wires about a year ago and would expect them to still be good. Did visually inspect those components though and they all look fine. I did check compression a couple months ago and #4 was the lowest at 150 but that was with a cold engine and after a quick shot of lube it was 160. So, I don't think think that's the problem. What I am concerned abut is the fuel filter and the coil. The car has 180k on it and I would bet that fuel filter has never been changed. The coil appears to be original and I should have changed it with all the other upgrades but I just spaced it. If anyone has any thoughts or advice I would certainly appreciate it.

Post by **Ozark Lee** » 22 Dec 2013, 21:21

Did you re-check the compression on cylinder #4? Given that #4 was low before and the misfies is reported on #4 that is where I would start.

...Lee

MoparWade · Post by **MoparWade** » 22 Dec 2013, 22:09

Just checked it again, cold this time too and it is the same. However, I noticed that the spark plug doesn't have the normal appearance. It doesn't look fuel fouled necessarily but it is missing the nice toasted brown carbon on the electrode. It's not wet it just looks oddly clean, if I didn't know better I would think it had just been put in and barely run. Could it be a failed or failing injector?

Post by **rmmagow** » 23 Dec 2013, 07:49

Get the exhaust gas in coolant check kit to verify no head gasket problems. Slight bit of coolant into a cyl will make the plug look clean. BUT it may well be the injector too, move it to another cyl and see if the miss follows. Change that fuel filter too, overdue.

MoparWade · Post by **MoparWade** » 23 Dec 2013, 13:23

Exhaust gas check done very recently while searching for coolant leak, heater core. Will move injector and see what happens.

MoparWade · Post by **MoparWade** » 23 Dec 2013, 15:13

Okay, so I just swapped the plug and injector for cylinder 4 with cylinder 5. Misfire remained with 4 so I'm going to get some new plug wires, cap and rotor and try that. It is only cylinder 4 so I am hesitant to think it is a cam sensor or crank sensor.

MoparWade · Post by **MoparWade** » 24 Dec 2013, 17:52

Don't think anyone is reading this anymore but I have swapped out ever piece that I am aware of that could cause problem in just cylinder 4 except maybe the CPS. I have heard of knock sensors causing misfires but I would assume that would be an issue across the whole cylinder bank.

Post by **Pauloil** » 24 Dec 2013, 19:11

Ozark Lee wrote:Did you re-check the compression on cylinder #4? Given that #4 was low before and the misfies is reported on #4 that is where I would start.

...Lee

did you see this?

MoparWade · Post by **MoparWade** » 25 Dec 2013, 02:30

MoparWade wrote:Just checked it again, cold this time too and it is the same. However, I noticed that the spark plug doesn't have the normal appearance. It doesn't look fuel fouled necessarily but it is missing the nice toasted brown carbon on the electrode. It's not wet it just looks oddly clean, if I didn't know better I would think it had just been put in and barely run. Could it be a failed or failing injector?

Yes, I saw and responded to it. I did make some progress tonight though. I found that the injectors don't fire in sequence but rather all at once. So, I swapped plugs for the injectors on 4 and 5 and took it for a brief but aggressive drive. Performed great, no CEL and no misfire. Thinking when I check the wires for the plug on the #4 injector in the light tomorrow I will find a bare spot that has been grounding out.

Post by **rspi** » 25 Dec 2013, 04:39

Nice find, I was thinking injector myself. Keep us posted.

Try to do your compression test warm. Wet number(s) should be near 185.