1998 V70 T5M Random Misfire Problem

Seaway · Post by **Seaway** » 26 Oct 2015, 04:48

What started as me thinking I had a drivetrain problem has been correctly identified as a misfire under load problem. Basically any heavy throttle input makes the engine vibrate - mostly between about 2800-4000 rpms, give or take a few on either end.

Thus far I have replaced the plug wires, the distributor cap and rotor and the plugs have about 1000 miles on them. They are gapped at .025 as I am running 17psi of boost with an ARD Green Tune and was getting spark blowout with the gap set bigger.

After replacing the wires the other day, the car ran beautifully for about 150 miles, and then the problem resurfaced. There is a slight "tick" randomly at idle, and under load there is a lot of vibration. I replaced the distributor cap last night and again, the idle cleared up and the car was smooth and strong under load, but the problems quickly came back. I then re-routed the ignition coil wire and it seems to have cleared it up on my commute to work this morning (read somewhere that the coil wire can interfere with the crank position sensor and create some weird misfires). I have a new ignition coil on the way today which I will put in - at that point the whole ignition system will be new - and hopefully that will be the end of it.

If not, the only other thing I can think of is a boost leak fooling the ECU into dumping more fuel than necessary under throttle input. Not sure that would explain the little tick at idle, however. Is there anything I am missing? There are no codes and no pending codes. I suppose I could swap in the stock ECU and see if anything changes.

Post by **abscate** » 26 Oct 2015, 04:58

Nice! Intermittent ignition stuff can drive you crazy, which is one. One of the nice things about the 1999-on plug on coil systems is the elimination of a lot of the ignition wear parts.

Seaway · Post by **Seaway** » 26 Oct 2015, 05:04

Hopefully if it is all new, it will all work... That is the hope anyway. I am putting in an MSD coil as it is about half the price of the stock coil. I will have to make up some kind of mount for it, but I can probably handle that.