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  #1  
Old May 25th, 2015, 12:31 AM
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Tristan Felchlin
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Intermittent stumble

So got the D90 running and out of the garage.
Replaced the pan gasket with some right stuff and fixed all of the leaks.
Replaced the injectors with mustang 19lb 4 hole variants

Took it out for a drive and right at about 2500-2800 rpm there is a bit of a stumble and lurch then continues on just fine.
No leaks at the injectors
No noticeable air leaks

CEL is showing the standard O2 fault.

Any ideas of where to look?
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  #2  
Old May 25th, 2015, 02:07 PM
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Tristan Felchlin
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Additionally there is an occasional backfire in that range.

Timing?
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Old May 25th, 2015, 02:09 PM
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Bill Adams
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Backfire is timing. Start at the distributor. Cap, rotor, wires plugs, amp module.
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Old May 25th, 2015, 07:41 PM
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Jason England
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Quote:
Originally Posted by o2batsea View Post
Backfire is timing. Start at the distributor. Cap, rotor, wires plugs, amp module.
stumble and backfire is probably an air leak. Check your hoses. The big one is the main culprit and can leak underneath where it rots through.

Unless you've played with the timing I'd start with air being the issue especially as you've had the plenum off to do the injectors.
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Old May 25th, 2015, 09:26 PM
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William
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Does it happen under pretty heavy throttle/acceleration only? Mine did something similar when under acceleration (around the same rpm). Turned out to be a bad Throttle Positioning Switch (TPS). Occasionally it also idled a bit high 1,500 rpm. How is your idle?
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Old May 26th, 2015, 11:46 AM
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Tristan Felchlin
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No it was under normal driving conditions. Discovered a line coming off what appears to be a PCV on the fuel rail was disconnected.

Didn't have time to see if that helped before I had to leave again. Will do timing next time I am home though. Was doing some reading and just verifying normal is 6 at btdc but it can be advanced to 8-9? Is that sound logic?
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Old May 26th, 2015, 11:59 AM
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Chris Davis
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That could cause issue due to vacuum leak--and it is worth checking out before continuing to other stuff. It would affect your timing via the vacuum advance on your distributor, assuming you are running one, among other things. Vacuum related issues have all sorts of symptoms...

As for timing, you can really go as high as you want before pinging, technically, which is usually around 10-14 depending on altitude (higher altitude, you can typically go higher). That doesn't mean you SHOULD and you have to be very wary of your total advance when you do. Running at 6 should not be a problem at all (nor should 8).

I'd connect and see if it happens--no need to create issues that don't exist. I have had a TPS sensor go out, but my stumbling at specific rpm (I believe mine was at 2400) was the alternator of all things--one of the diodes went out (so it was still charging) but it bled AC into the system that cause my fuel injectors to fire right at 2400 rpm. That took a while to find out... That can also be checked, easiest at an autozone or such place, but possible with the right meter at home if you know the procedures....
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Old May 26th, 2015, 11:17 PM
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Quote:
Originally Posted by Coug D90 View Post
No it was under normal driving conditions. Discovered a line coming off what appears to be a PCV on the fuel rail was disconnected. Didn't have time to see if that helped before I had to leave again. Will do timing next time I am home though. Was doing some reading and just verifying normal is 6 at btdc but it can be advanced to 8-9? Is that sound logic?
Check the timing with the vacuum advance disconnected and if it's around 6 +/- 1 BTDC leave it alone until you've sorted everything else out.
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