09-20-2010, 11:09 AM #1
Another Backfire and some answers
Well I lost another intake manifold recently due to backfire. I can explain some of the conditions which lead to this event but not all ..... at least not yet. Reading through some of the other posts and based on my experience the backfires are caused by excessive fuel left over after a cold start. Now if the motor is started and then warmed up you will probably never experience a backfire as any excess fuel will be burned when the motor runs and warms-up. But if you start the motor and have too much fuel being dumped in and don't warm it up, wait 18- 24 hours such that the excess fuel vaporizes and mixes with air in manifold then you could have damaging backfire on your hands.
If you have a stock ECU and have not messed around with RRFRR or other fueling tweaks then don't be concerned as the stock ECU has been well calibrated to minimize these conditions. But if you are using an aftermarket ECU or modified fueling ( particularly at start ) in some way then be careful when doing multiple cold starts without warming up the engine.
That being said does anyone have an intake manifold for sale ?
09-20-2010, 11:19 AM #2
the only time i have ever hadmy ski backfire the tb sensor was bad
09-20-2010, 02:00 PM #3
09-20-2010, 02:46 PM #4
- Join Date
- Aug 2009
- Discovery Bay, CA
I would think injector issue too.... that being said i saw duke had 2 manifolds for sale about 2-3 weeks ago he may have one. Good luck
09-20-2010, 04:05 PM #5
Thanks guys. Leaky injector definitly not the issue ..... I have checked this many times with the manifold pulled back from head and the injectors and fuel rail connected and pressurized. Cam timing seems o.k. as the motor turns 8700 - 8800 RPM and pulls strong. Intake valves are sealing good as pressure checked intake tract and it holds 25 psig with very low leakdown.
The backfire problem started when I started messing with cold start fueling in my ECU. Trouble is that the motor now cold starts great ( provided it doesn't backfire ). However this apparently requires way more fuel than it should so now I'm thinking injector timing is off or the like. After the last backfire I pulled the plugs, disconnected injector wires, cranked the motor and a significant amount of fuel mist was be pumped out of the spark plug holes. It looked the motor had been flooded but I know it would have started and run smooth.
09-20-2010, 04:08 PM #6
09-20-2010, 04:19 PM #7
It's a Motec but I don't want people to think that it is to blame as I'm the one programming it ! Most ECU's are not prograble so the only way to overfuel is with oversized injectors or too much fuel pressure
09-20-2010, 04:48 PM #8
09-20-2010, 05:54 PM #9
I have Motec in the loop ...... but good idea. My last solution was to run a script on my on-board PC connected to the Motec via USB which triggers a cranking purge but this was only a band aid and did not eliminate the problem. Any ideas are welcome.
09-27-2010, 08:20 AM #10
Well I finally got to the root cause of my problem. There was a setting in my map to inject fuel with the engine stopped when the TP exceeds 90 %.....sort of like pumping the pedal on the old carburated automobiles. In my case I had the laynard on the post and was stroking the throttle without starting the motor. The fix was easy just change the map to eliminate this injection.
BTW a leaky injector would caused a very similar condition so if you experience a backfire in the intake manifold you probably have a leaky injector.
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