Misfire under boost

[turbo84voyager]

I am experiencing a missfire / slight backfire under boost. I had a similar problem a few weeks ago and turned out it was a lean condition caused by a bad fuel pump. I replaced the fuel pump with a new aeromotive stealth and the issue got better but now it pulls hard to about 15 psi and then it has a slight missfire at part throttle and at WOT it will do the same but also have a light backfire. I checked my fuel pressure at idle and its right on. I tried different known good calibrations with no difference. I removed the AR51 plugs and put a set of 9yc plugs and I think it got a little better. Now when I had the problem with the fuel pump when I tried the 9 plug which is hotter than the 51 it had a nasty backfire. It is nothing like that now. It seems to be more load related and is worse when it is under more load. I didnt get a chance to borrow the fuel pressure gauge with a long hose to drive it again but I pinched off the return line and it spiked to over 100 psi also when it misses the wideband and dawes does not go nearly as lean as it did. It may go into the 13's but that is probabily from the unburnt fuel. The one time when it did this it cleared right up after a few seconds. I tried a different coil and it seemed to help out a little at part throttle but not much at WOT. Any ideas?

Thanks!

Justin

[Vigo]

My only idea is that it seems ignition related. Might try gapping the plugs really tight and see if it goes away, that would verify ignition.

[black86glhs]

Set the gap at say .025 and see how it does.

[turbovanman²]

Which vehicle? What setup? What are you using for ignition components? Ignition and cam timing triple checked? Codes?

[turbo84voyager]

Sorry for not stating which vehicle, I dont know what I was thinking . It is my 89 caravan 2.5 turbo. Anyway read on the forum about a few people having blow out and they gapped the plugs smaller so I regapped the plugs to .030 this morning ( they were .035 ). I did a WOT run this morning and a few 16 psi part throttle runs and I did not feel any missfire. Any problems if I just run it with the .030 gap or should I get a hotter coil?

Thanks!

Justin

[Vigo]

Unless you have some high-dollar plug wires on there i would consider that a possible problem. Maybe swap wires from one of your other 2.5s and open the gap back up and see? Or just live with it, .030 isnt going to do anything but maybe cost you 1% power out of boost.

[turbovanman²]

Sorry for not stating which vehicle, I dont know what I was thinking . It is my 89 caravan 2.5 turbo. Anyway read on the forum about a few people having blow out and they gapped the plugs smaller so I regapped the plugs to .030 this morning ( they were .035 ). I did a WOT run this morning and a few 16 psi part throttle runs and I did not feel any missfire. Any problems if I just run it with the .030 gap or should I get a hotter coil?

Thanks!

Justin

Unless you have a flame thrower coil, .035 is too big. .030" or less with a stock type coil and I think spec is .030 from the factory anyhow, :p