88 F-150 302 M5OD tranny 4x4......she runs rich...waaaaaaaaaaay to rich. FPR, TPS, IAC sensors have all been replaced. Truck has longtube headers with no bung for the O2 so it's hangin. But a buddy of ours has an SD truck with the same exhaust and the O2 hangin and his doesn't run NEAR as rich. We're talkin so rich that it looks like a diesel gittin on it there's so much black smoke pouring out. MAP sensor has been replaced but the vacuum to it is disconnected because the truck stumbles and dies on itself with it connected. No change in this behavoir with a good MAP sensor.Won't show codes with paperclip...I think the CE light is bad??? I'm sure I'll think of more but this is all for now...

fix that O2 sensor first...

and chek for codes

Yeah I'd fix what you know is broken first. That o2 sensor hangin' is a bad idea. It's probably sensing way too much oxygen since it's not in the exhaust pipe, which would make the computer want to dump more fuel to even out the A/F ratio. Just shootin from the hip.

Already thought of that and tryin to hunt down some factory pipe...but like I said know someone with another SD truck with the 02 hangin and his does NOT act like this truck...

Every truck is a different beast. Who knows why his doesnt run the same...?

flareside_thunder said:

88 F-150 302 M5OD tranny 4x4......she runs rich...waaaaaaaaaaay to rich. FPR, TPS, IAC sensors have all been replaced. Truck has longtube headers with no bung for the O2 so it's hangin. But a buddy of ours has an SD truck with the same exhaust and the O2 hangin and his doesn't run NEAR as rich. We're talkin so rich that it looks like a diesel gittin on it there's so much black smoke pouring out. MAP sensor has been replaced but the vacuum to it is disconnected because the truck stumbles and dies on itself with it connected. No change in this behavoir with a good MAP sensor.Won't show codes with paperclip...I think the CE light is bad??? I'm sure I'll think of more but this is all for now...

Click to expand...

Won't show codes with paper clip? Umm, was the CEL output even wired to a light in the 88 trucks? I know it wasn't on an '86 'Bird. Trucks tended to lag the cars quite a bit back then because emissions regs weren't nearly as tight for trucks. If it is, that O2 hanging should be setting a code disconnected. Is the O2 sensor actually there, or just the connector hanging down? Here's a little trick. Disconnect the EVP (EGR Valve Position) sensor. Warm the engine. As soon as it's warm enough for closed loop, lack of the EVP signal will DEFINITELY set a code, and turn on the CEL. If that doesn't happen, better get a light bulb if it actually has a CEL on the IP. Plan B would be to hook up a light as shown on www.fordfuelinjection.com. Good site for EEC issues.

No O2, though, yeah it would run pretty rich, and may even go to 'limp' mode. Limp mode will just about suck a dent in the tank because it uses fuel so fast.

O2 sensor is there but hanging...

Your EEC should be throwing codes like it's got diarhea, then. Would probably be better with no O2 at all than one that's hangin in the breeze. If it ain't bein smothered with exhaust, it's going to turn the injectors way up, thus your smoking like a freight train when you gouge it.

I've actually disconnected mine for some troubleshooting with a lean miss. While it didn't tell me the real problem (leaking plenum gasket) it did throw a code after the truck got up to operating temperature. RELIABLY, the CEL would come on within 8 minutes of starting the engine with the HEGO disconnected. What it did NOT do, though, is run rich. It wasn't as efficient as it could be, but it never smoked. That was probably in part due to the leaking intake and failing ACT, though.

If your header's got a bung, get that HEGO mounted. If not, get a muffler shop to put you one in. Even if you only monitor one side, if it's bank fired, also read Speed/Density, it won't make much difference just monitoring one side. It won't let you know if you have a fouled injector on the other side, though.

I probably worry a lot less about the emissions issues than I do the driveability issues. Without the O2, the EEC cannot go into closed loop performance and will not optimally control the A/F mixtures. There's a reason for each of the sensors (feedback). The EEC is little more than a control loop that requires various feedbacks and weights them accordingly.

You need the MAP also, if its disconnected and wont run you got probs, remember when Jurgen unplugged his MAP and the truck ran real bad and smoked. You can get a O2 bung at any performance store and drill a hole and weld it in, even a nut welded onto the pipe will work. I know when I took the snap-on scanner home, with the old school ford connectors it wouldnt read my bronco, but doin the paper clip did work, and an 88 bronco has the ck engine light. Yours might be pulled out.

flareside_thunder said:

MAP sensor has been replaced but the vacuum to it is disconnected because the truck stumbles and dies on itself with it connected. No change in this behavoir with a good MAP sensor.Won't show codes with paperclip...I think the CE light is bad???

Click to expand...

This sounds like a FUBAR'd computer to me. The fact it won't spill the codes and it runs worse with the MAP connected really points the finger at the EEC. These computers are programmed with an open loop strategy in case one of the main sensors(O2 and MAP) goes bad, it's programmed to apply enough fuel for roughtly 13.5:1 A/F ratio which is rich but not black smoking rich.. so something is definitely royally screwed with this one, it should run more like the other SD truck you mentined.

we've already swapped in two other computers with no change.....both the others are for the same setup and are SD.

EDIT:Something new has arrived. Pulled the oil dipstick and it smells like fuel...I'm thinkin intake gasket.....any thoughts?

If you're smelling gas in the fuel then I'm thinking bad rings. You sure the smoke out the tailpipe isn't blue?

Running waaaay too rich will dilute the oil aaaaand wash the rings...

oh O2 sensor is unplugged as well.....

OK..
Does it hold fuel pressure when the engine is shut off?
What is the fuel presure?
Is the FPR leaking fuel out the vacuum line?