Missfire under boost

[turbo84voyager]

Hi,

I am experiencing a missfire at about 16 PSI. The van pulls hard up to the 16 psi then it starts breaking up. At the time it starts breaking up ( missing) I get CEL on for what I am guessing is knock. I dont hear any knock and the light does not go on at all when it is not missing. It is pretty consistant at 16 psi at Part throttle. I did not try WOT. I pulled about 2 degrees of timing out at this point but it is still there and I still get the CEL. I am running the Turbonator ( last years version) 3 bar 40 + cal. I am running the autolight AR51 plugs. The plugs look fine. AFR's are around 11.3 when it does this. When it starts missing the AFR's go up to the high 12's low 13's but that is probabily because the missfire is not burning the fuel and causing the O2 to think its lean. I am not sure if mabe I have a weak coil. Has anyone ever experienced a problem like this or recommend where I should start looking.

Thanks,

Justin

[ShelGame]

What version of T/SMEC is it?

[bakes]

What is your current plug gap if you can drop it .024 for testing if the miss goes away look into the igntion system for weak links

[turbo84voyager]

Im Running V16 turbonator. As for plug gap, I didnt check the gap when I had them out but I gapped them to stock specs. The only thing is the AR 51 plugs have grounding electrodes that only go to the corner of the center of the plug. Hard to describe, basically looks like someone removed some of the grounding electrode. I have been running these plugs in the past with no problems but I will have to try a smaller gap.

[mpgmike]

Try replacing your coil with the newer style that bolts to the T-stat housing. This gives you 2 advantages. Firstly, the coil has higher output than the older oil filled original. Secondly, it requires a shorter coil wire (less resistance).

Mike

[ShelGame]

Im Running V16 turbonator. As for plug gap, I didnt check the gap when I had them out but I gapped them to stock specs. The only thing is the AR 51 plugs have grounding electrodes that only go to the corner of the center of the plug. Hard to describe, basically looks like someone removed some of the grounding electrode. I have been running these plugs in the past with no problems but I will have to try a smaller gap.

Is it version 16.0? You'll probably have to open the .asm file in notepad to tell. The revision history is near the top of the listing. If it's 16.0, that's your problem. I had tried to re-scale the Pumping Efficiency to range from 50-150%. And, it didn't work. Occasionally it caused an overflow that would send the PW to near 0.

There were other changes to later version that might also be the issue. Before you try too hard to tune it out, I'd try the latest version.

[turbo84voyager]

Mike, I will try one of the newer style coils. I know the current coil was replaced at one point but since pretty much all aftermarket replacement parts are junk any more it could definately be weak. The more and more I think about it, consistancy of 15 to 16 psi makes me think it is something else though.

Rob, I will check the version when I get home this evening. I believe I have the version where this was fixed. I did have the problem a while back where it would have an occassional missfire but I cant remember exactly what the cause was. I remember you sent me a fixed version to test for you and it resolved the missfire I had at that time. I am thinking it was the pumping efficency problem. The engine does not miss at any other point and pulls hard and it feels like I hit a rev limiter at about 16 psi.

[turbo84voyager]

I was running Turbonator V16.3. The problem is there at WOT as well. I pulled the AR51 plugs and installed an almost new set of RN9YC champions. I checked the gap and they are at.032. I took it for a ride with the other plugs and it was worse, I had a loud backfire ( almost thought I blew out the muffler). I tried again and right before it happened I swore I saw my wideband jump to the 14's. I pulled the Cal and installed a FWD cal I had. It is not as agressive as mine. I took it for a ride and the same breakup / missfire and a little backfire as well. I was watching the A/F and I dont believe it went nearly as lean. Prior to it the A/F was in the high 10's. Any idea where I should start looking next? It runs fine under 15 psi. Thats what scares me the most, I dont like having this problem at a higher psi of boost. I checked for codes and I am getting a code for an internal ECU error and that it cannot calculate mileage. I am assuming these are just from the cal.

Thanks

Justin

[bakes]

Check your I shaft

[turbo84voyager]

What do I need to look for on the I shaft (im assuming the accessory ( oil pum / distributor) I didnt know there were problems with the SOHC shafts.

[ShelGame]

I was running Turbonator V16.3. The problem is there at WOT as well. I pulled the AR51 plugs and installed an almost new set of RN9YC champions. I checked the gap and they are at.032. I took it for a ride with the other plugs and it was worse, I had a loud backfire ( almost thought I blew out the muffler). I tried again and right before it happened I swore I saw my wideband jump to the 14's. I pulled the Cal and installed a FWD cal I had. It is not as agressive as mine. I took it for a ride and the same breakup / missfire and a little backfire as well. I was watching the A/F and I dont believe it went nearly as lean. Prior to it the A/F was in the high 10's. Any idea where I should start looking next? It runs fine under 15 psi. Thats what scares me the most, I dont like having this problem at a higher psi of boost. I checked for codes and I am getting a code for an internal ECU error and that it cannot calculate mileage. I am assuming these are just from the cal.

Thanks

Justin

You can turn that code off easily in T/SMEC; Just go to the CONFIG2 flags and select 'Supress EMR'.

[85boostbox]

What is your fuel pressure at? I would start with basics first. Sounds like a fuel problem to me.

[Force Fed Mopar]

I currently have the AR51 plugs also, and I have run up to 22psi without spark blowout. So I would guess that's not the issue. The gap on the AR51 plug isn't really adjustable, as you say it doesn't reach over top of the electrode, just goes to the corner of it. IIRC the gap is like .017" or so.

I would upgrade to V18 and see how it does. It is possible it's the coil or coil wire also. Or a fuel issue, as mentioned above. AFR reading lean could indicate the pump is running out of volume, either too small a pump or it's getting weak.

[trannybuster]

What do I need to look for on the I shaft (im assuming the accessory ( oil pum / distributor) I didnt know there were problems with the SOHC shafts.

Neither did I at one time, then I failed two of them. Check your timing with timing light, its fast and easy to check no.....my issue was same as yours, blowout...

[85boostbox]

To add to my comment there are 3 reasons why I suspect a fuel problem" 1 It is always happening at 15-16 PSI boost, 2 When it happens you get high AFR's and 3 It is happening all the time whethere you are WOT or part open throttle.

[thx138]

I had a similar issue (at around 18/19 psi). Tried different plugs and gaps (ended up with the autolites). Was using magnecors and a blaster 2. MSD 6AL2 fixed the issue as soon as it was installed. So I assume this was a blow-out issue and the MSD box was a band-aid but it has work fine up to 25/26 with no issues. (The 2 step limiter was an added bonus).

[turbo84voyager]

Before work, I swapped the coil and coil wire with my shadow, I had a new 3 bar map I threw on, checked the timing and adjusted it to 12 degrees. I know I had it backed off a little. I installed my fuel pressure gauge and I am running approx 50 psi at idle and about 58 psi with the vacuum line off. while driving, it was doing the same thing. I did take notice that if i am cruising down the road and get on it ( about 1/2 throttle) the A/F jumps to about 13.5 and then appears to slowly lean out. I would expect it to do the opposite. It must be doing this because I glanced down while merging into traffic and at about 8 psi the A/F was in the low 14's which should be way too lean. This is making me think it is slowly running out of fuel. I am going to try changing the fuel filter. I have been thinking about it, it has not been changed in about 6 years, about 20k ago. It has the 255 pump and that was put in about 4 years ago. Other than a weak pump I dont know what else could be causing the problem.

[turbovanman²]

I would do a volume test, it should be at least one pint in 30 secs.

[turbo84voyager]

I changed the fuel filter. It definately was not blocked. I did get some junk out but it had some water in it as well. Took it for a ride, same miss / backfire. I am thinking I had gotten some bad gas. I removed the fuel line and jumped the pump relay. There definately is no volume problem. It filled a beer bottle in a few seconds. It has a 255 lph pump. The fuel in the bottle does not look real golden like gas usuially does and when I smell it I can smell more of the beer residue then gas. I poured some gas I had for the mower ( from another gas station) in another bottle and you can definately smell it and it is more golden. I am going to drain the tank. Yes it is filled to the top

One strange thing, before I removed the fuel line, I pressed on the shrader valve to remove the pressure. I believe I got more air out of the rail than gas. Any idea why? Even when I pulled the fuel line there appeared to be quite a bit of air.

[turbovanman²]

The supplied hose isn't very good and can break down, the one inside the fuel tank. I would also check to make sure the clamps are tight, the pick up o-ring is still there and the pick up is properly installed. Its easy to do after you drain it.