I have a '97 5.0 out of an explorer (gt40p I believe) in my Ranger, with a small remote turbo @ 5psi, 255lph walbro hi-pressure, 39# injectors, AEM air fuel gauge (wideband), 90mm lightning MAF. PCM tuned by Sniper Special Forces (which I no longer have acces to).
A/F ratio was tuned to richen down to 11.7 (actual 11.6-11.9 on a/f gauge) when you get heavy into boost. All of the sudden it no longer does that and remains the constant 14.7 (14.6-15.1) even into boost which is dangerous as I understand it. What could cause this? I'm told the PCM can't 'lose its tune' (but it sure seems like it), so what mechanical mechanism can be fooling the computer into not richening the mixture?
It also has a miss (stutter) while at cruise speed (about 2000rpm/65mph on the highway). So far I've changed out a fuel pump, new plugs, fixed a broken EGR rubber hose (blowtorched my heater box). Have a new plug wires and DPFE on the way. Idles great, runs great under any kind of minor (or even major) acceleration.
I'm at a complete loss, and I'm skeptical my local (and only near) dealer will be able to get a grip on this custom application. Any advice would be greatly appreciated.
If you have access to a scan tool that has a live data feed mode, make sure you when you put the pedal to the floor, the throttle position sensor reads 100%. If the throttle position sensor will not read 100% throttle, or close to it when wide open, then the computer will never go open loop and use the richer mixture.
__________________
- Ian
1987 Ford Ranger XLT 4x4 2.9
Needs a lot of work, including some rot on the body, but shes getting there.
Is this setup using a MAP sensor to measure boost? If so is this device operational and is the vacuum line attached and intact? Are there any codes in the computer?
__________________
Paul O
1990 F150 4x4 XLT X-Cab 5.0, 3.55LS, Comp XE264HR-14, Flowtech LT's to 3" single, FRPP Mass Air Conversion, TweecerRT with BE, Innovate LC-1 wideband O2
No related codes so far, but I will be checking again sometime next week, as well as a fuel pressure check hopefully. Boost/vacuum gauge is working properly I believe, but I'm not sure where it measures at; I don't beleive it uses a MAP sensor, the MAF takes the place of that I believe? The Maf appears to be clean and operational, though I don't know how to test voltages to know for sure.
Yeah if you don't have an FMU in the fuel system then fuel enrichment is strictly under computer control.. which means the tuner is no longer doing it's job.
__________________
Paul O
1990 F150 4x4 XLT X-Cab 5.0, 3.55LS, Comp XE264HR-14, Flowtech LT's to 3" single, FRPP Mass Air Conversion, TweecerRT with BE, Innovate LC-1 wideband O2
I apologize as I don't think I'm stating things correctly for you to understand. The Explorer PCM (computer) was reflashed with a new tune, the PCM knows (or knew) to enrich the mixture when it was supposed to. I'm told this is stored in permenant Read Only Memory and can't be lost (even though it seems like it has). Therefor there must be a sensor somewhere that is not sending incorrect information to allow the PCM (with its new parameters) to run things correctly. Or is the PCM itself bad?
I keep thinking something in the EGR system, as the ruined hose to the DPFE occured generally at the same time as the miss at ~2000rpm, and the problem with a/f ratio. Maybe its coincidence though, and something else is up? New plug wires and DPFE going in soon. After that I guess its on to coils and throttle position sensor? I'm really needing a good scanner for this rig, Christmas may have to come early this year. Thanks for the help so far gents, all help is greatly appreciated.
If you have a buddy with another 5.0 EFI, I'd try seeing if you can convince him to let you borrow his TPS and see if it makes a change. A computer will not just loose its programming.
__________________
- Ian
1987 Ford Ranger XLT 4x4 2.9
Needs a lot of work, including some rot on the body, but shes getting there.
I understand what you're saying.. my comment about the FMU refers to another type of boost compensation that you are obviously not using. If the PCM can be reflashed it can also lose the new calibration..though this should not just happen for no reason. A problem with the TPS or MAF meter could cause this type problem but that should also throw a code, so maybe your computer did lose it's programming. A scanner will tell the story.
__________________
Paul O
1990 F150 4x4 XLT X-Cab 5.0, 3.55LS, Comp XE264HR-14, Flowtech LT's to 3" single, FRPP Mass Air Conversion, TweecerRT with BE, Innovate LC-1 wideband O2
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.
