TD New Guy
Join Date: Jul 2012
Location: North Alabama
My Ride: omnivator
Engine: 2.5 TII
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Powerful BACKFIRE-- everything looks good cannot figure it out
I'm resurrecting my 2.5 TII Petersbuilt powered Omni GLHT and cannot get over a backfire problem. The car ran fine 18 months ago and now I have "fixed it all up" and am experiencing BAD backfire at the boost peak, right after hitting the boost limiter while I am attempting to train the SMEC on the boost limits.
Normally it takes a half a dozen acceleration cycles to train the ECU but I can't get the ECU to learn the ropes this time. Maybe it is the "squishy" heavy duty vacuum/boost line I have for the wastegate instead of my normal hard nylon line but it never did this years ago before I learned about hard vs soft lines so why now.
The SMEC is from FWD performance. The only significant change made that I can think of during the rebuild is changing the wastegate actuator from the small can (originally installed per recommendations from Neil with his custom SMEC) to the large can (sold by Turbos Unleashed and recommended by Cindy for the FWD perf SMECS). It is a high compression (9:1) engine but that is not important?
The timing is good-- started at 9 deg BTDC moved it to 6 deg BTC for trouble shooting,
I checked the cam timing and it is 4 degrees retarded (1/2 tooth),
plugs old but good,
wastegate actuator is properly connected and brand new
exhaust is hooked up,-- might have a pin hole 4 feet downstream of the turbo but most likely not...I'll check soon. But a pin hole causing this backfire is not likely.
vacuum at idle about 20 inches Hg
No codes except non important 12,22,42
timing light indicates no significant misfire at idle
Fuel in fuel tank is old but ?? 100dB misfire from bad fuel???
Fuel rail holds 50 psi for an hour after shutdown so fuel injectors not leaking much
There is a vacuum leak from the HVAC system but presumably very small (Can't hear it but the heater control system is totally destroyed) so I know there is that one leak in the HVAC system to be repaired after I get this hog running again.....
Fuel pressure gage on fuel rail shows that the fuel pressure regulator is working when I rev the engine in the driveway, It worked fine 18 months ago...
I can't imagine ANY of these minor (non)issues causing this severe problem... I've been playing with these cars for years and have heard a backfire like this before before. The last backfire was so severe I felt it strongly in the floorboards and it left a huge black cloud behind me that appeared to be two lanes wide by 3 car lengths long, it obscured the vehicles behind me until they passed through the cloud.
EGT is around 800 degrees at idle and I have been attempting to get readings at WOT of the EGT and O2 sensor voltage but cannot get the engine controller to stabilize at full boost to get a good reading. It looks like there is a good 0.95 volts on the O2 sensor at WOT at least but that is while I'm feathering the throttle to keep if off the boost limiter. As many of you know the EGT has quite a time delay so under these conditions I cannot get a good reading but there is no indication of running lean.
I looked at the plugs, all OK, have pictures, have not done a compression test but it idles great and exhaust sounds normal as it did 18 months ago. 2.5 inch CAT FREE all the way back to the ultraflow with 3" tip.
Any ideas? At this point I'm dumbfounded and planning to put it back together (after diagnostic disassembly of timing and vacuum systems) and attempt to retrain the SMEC for proper boost limiting. I see no reason why putting it all back together like it was will make any difference so I am ready go give up and trash this OLD POS. I've been working on this "simple rebuild" since September 2, 2012 and cannot devote any more time to this project. TIme to park it back out in the rain and snow an let it rust away for the winter then scrap it in the spring? Very frustrating. I thought I was a top notch TII mechanic but have met my match and cannot spend any more time on this. I have to move on. I am discouraged more than ever.
Lots of good parts in this one... built by a professional engineer with lots of money and time between 1993 and 2000. This is the third Dodge Omni turbo in my learning curve. There are 38000 miles on this awesomely blueprinted customized optimized heavily Peters influenced engine. Full Cage. Custom adj Konies, Coilovers. Positraction. Caster/camber plates. Lots of instrumentation. Strut braces front and rear. This car is built well. It is set up to take 8" rims with 225mm wide tires at 35mm offset. minivan brakes with 7/8" master cylinder. (awesome brakes) I do not take short cuts building mechanical equipment. I cannot believe it but I am stumped and don't know what to do next. I've searched this entire website multiple times for backfire and not a single post comes close to describing what I am experiencing.
This has got to be a simple problem.... What am I missing? I have never heard such violent backfires in all of my life. I warm it up, a little jump in first, floor it in second-bouncing off the boost limiter, third, bouncing off the boost limiter while kind of feathering the throttle to avoid total boost limiting and then POW!! ooooo time to go home.
Thanks in advance for any comments, offers to purchase, or advice.