O2 Sensors Not Reading Correctly? Holy Crap! I Think It's Fixed!!! Post #49

[Steve83]

Crankshaft throws are identical for 13726548 and 15426378 firing orders. Crankshaft doesn't care which cam is used.

So there's no reason to change the camshaft, right? Bank-fired EFI doesn't care what the firing order is (banks are the same) and SEFI can be rewired easier than a cam change.

 

[70_Steve]

I thought I'd summarize a couple threads and all the posts into one, to help someone if they're doing a search for the 41 and 91 EFI codes.

PROBLEM:

This is a new EFI conversion on a freshly rebuilt 351. The engine will start, but idles poorly with random misfires, and the exhaust smells very rich.

TROUBLESHOOTING:

KOEO codes 81, 82, 85 and 84. CM codes 11. KOER codes 41, 91 and 33. The KOEO codes are for all the emissions stuff I’m not using. CM code 11 is Pass. The KOER code 33 is for the EGR valve I’m not running. But the 41 and 91 codes are Left and Right bank lean.

Verified proper operation of the TPS, and also replace with a spare. No improvement.

Replaced the ECT. No improvement.

I verified 12 volts to the O2 sensor heater, and a proper heater ground. I verified the proper operation of the O2 sensors on the bench with a propane torch. Reinstalled and ran the engine with a DVM hooked between sensor output and ground. With the engine idling, the DVM showed less than .1 volt. But goosing the throttle would make the voltage jump up to more than .7 volts. Looks like the O2 sensors really are working.

Replace the MAF sensor with a used spare. No improvement.

Checked the exhaust system up to the O2 sensors to verify there are no exhaust leaks that would let fresh air into the exhaust stream and affect the O2 sensor reading.

Looked at the plugs and noted that they were much whiter than normal. I also noted that my nickel plated headers turned blue at the cylinders. Looks like it really is running lean.

Also had it confirmed that even with a lean mixture, if it’s lean enough to misfire, the exhaust will still smell rich.

THE FIX:

I replaced the MAF housing with a spare, started the engine and it idled perfectly.

What I noted was that the hole through the spare looked a little smaller than the one that was installed. I also noticed sanding marks around the middle of the one that was installed. I used an inside micrometer and measured the bore of each MAF housing. The spare, that made the engine idle correctly, measured exactly 55mm. The one with the sanding marks in the bore measured 56.5mm. Apparently enough of a difference to screw up the air flow indication.

Ebay buyer beware!!!

 

[Viperwolf1]

So there's no reason to change the camshaft, right? Bank-fired EFI doesn't care what the firing order is (banks are the same) and SEFI can be rewired easier than a cam change.

No need to change cams when adding SEFI. Rewiring injectors will cause additional unfixable problems caused by the O2 sensors now each reading 2 of 4 wrong cylinders.

 

[AZ69EB]

Steve,
Congrats!!! Cherry Creek run is in two week. A great time to put a few easy miles on your Bronco.

I hope you make it.

 

[stretch]

Steve,

Congrats at finding your problem. I glad it was something as simple as the MAF.

My problems were exactly the same as yours, and the new MAF fixed it as well. Purrs like a kitten. I'm just not as close to driving mine as you are. Maybe a couple more months. At least thats what I tell my wife;D

 

[toddz69]

I
THE FIX:

I replaced the MAF housing with a spare, started the engine and it idled perfectly.

What I noted was that the hole through the spare looked a little smaller than the one that was installed. I also noticed sanding marks around the middle of the one that was installed. I used an inside micrometer and measured the bore of each MAF housing. The spare, that made the engine idle correctly, measured exactly 55mm. The one with the sanding marks in the bore measured 56.5mm. Apparently enough of a difference to screw up the air flow indication.

Ebay buyer beware!!!

Wow!! Glad you were finally able to figure it out, Steve! What a nightmare.

Todd Z.

 

[70_Steve]

What a nightmare.

Yes, it was quickly getting to that point. I'm not sure how long it would have taken me to resolve this, had I not already had a spare MAF laying on the floor...

 

[NJB71]

Congrads Steve! Its awesome isnt it! Bronco runs like a champ, happy it worked out for you, DirtDonk wanted me to measure my MPG, but everything I am running is made to go fast.....besides my right foot weighs 100lbs at least, so do u want to take over the responsability?
Stephen

 

[HoosierDaddy]

In an effort to stop the hi-jack , here is why you DO NOT swap the injector wiring to match your non-HO firing order :http://fordfuelinjection.com/?p=92

Holy Smokes Steve , good catch on the size differences and what it will do to your EFI'd motor. Great info.