EFI Codes and Troubleshooting

[broncosbybart]

Lately the racer has been acting up. It runs well when cold, but when it gets to operating temp it will backfire and throw the check engine light on for a few seconds after the backfire. Backfiring only happens during hard acceleration. It is a stock Explorer engine, no EGR or emissions stuff, 70mm MAF from a crown vic or similar- the one that should work, sensors are about 1 year old.

I have a few codes being thrown. 31, 81, 82, 85, 84. These all come up on the KOEO test. In memory are codes 29 (VSS- which isn't used), and 31.

The truck used to run fine. I am thinking that the MAF could be dirty (again) and will clean it. I hate stabbing in the dark.

From what I have seen on the oldfuelinjection site, code 82 should only come up on a KOER test. No idea if that is right or not. I have not run a KOER test yet.

What do you all think? These 2 digit codes are hard to do a search for, as the search feature only starts with 3 characters.

 

[Amac70]

http://oldfuelinjection.com/?p=14

 

[Viperwolf1]

Nothing significant in the codes. Could be dirty MAF or low fuel pressure.

You can get all those codes during KOEO.

 

[broncosbybart]

Thanks for the reply. So crazy question here in a few minutes:

I took out a plug and it looks like it is running lean. I do plan to replace the vacuum booster as I suspect it could be leaking. The backfire issue also seems to validate the lean condition at operating temps.

If I can't find the source of the problem before the race next weekend, any thoughts on using the engine temp sensor input to replicate a cold engine condition for the duration of the race (about 1-1.5 hours)? That should cause the engine to run richer, right? Ghetto I know. Just not sure how much time I'll have to tackle the fix.

 

[Viperwolf1]

No way of predicting how well that will work. My guess is "not very". Do you really want to race with a lean engine? No time to fix but maybe enough time to swap a blown engine?

Unplug the MAF and see if it runs better. Vac leak should be easy to find also. Fuel pressure just takes a gauge.

 

[chuzie]

My fuel pressure gauge is the single best thing I ever added to my EFI system. Instant feedback and elimination (or inclusion) when troubleshooting issues, no guess work. If it's not pressure, that leaves scheduling. If it were scheduling I would imagine a code would be thrown unless the MAF is not dorked up enough to be out of limits. Have you run a KOER test? Viperwolf has a good point; see what happens unplugged.

 

[broncosbybart]

yeah, i think a fuel press. gauge will make its way to the gauge panel soon.

cleaned the MAF and replaced the vacuum booster. runs well now. keeping my fingers crossed... ordered another MAF that I will be bringing to the race with me this weekend. i've got to find a good cone style air cleaner. using a K&N right now (going light on the oil for the thing). tried a dry style 'riceburner special' type and it didn't work worth a crap.