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  #1 (permalink)  
Old 10-30-2009, 11:08 PM
Lignite Lignite is offline
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Air/fuel ratio won't richen under boost

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.
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Old 10-31-2009, 09:46 AM
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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.
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Old 10-31-2009, 09:47 AM
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Conanski Conanski is offline
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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?
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1990 5.0HO AOD XLT X-Cab F150 3.55LS, 1994 3.0L 5-sp x-cab Ranger 3.45, 2004 3.0L 5-sp X-cab Ranger Edge 4.10, 2004 2.5L 5-spd Subaru Legacy
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Old 10-31-2009, 02:37 PM
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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.
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Old 10-31-2009, 05:26 PM
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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.
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1990 5.0HO AOD XLT X-Cab F150 3.55LS, 1994 3.0L 5-sp x-cab Ranger 3.45, 2004 3.0L 5-sp X-cab Ranger Edge 4.10, 2004 2.5L 5-spd Subaru Legacy
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Old 11-03-2009, 10:33 AM
Lignite Lignite is offline
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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.
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Old 11-03-2009, 01:38 PM
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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.
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Old 11-04-2009, 12:50 PM
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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.
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1990 5.0HO AOD XLT X-Cab F150 3.55LS, 1994 3.0L 5-sp x-cab Ranger 3.45, 2004 3.0L 5-sp X-cab Ranger Edge 4.10, 2004 2.5L 5-spd Subaru Legacy
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Old 12-17-2009, 08:59 AM
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Just my thoughts: I would check the A\F sensor and monitor and calibrate them, if possible? Also check your O2 sensor, if yours is still hooked up(factory) or after market, calibrate or replace if possible.Yes if your A\F is reading correctly this is dangerous. Pull a plug and read it to see if you are actually running lean.If it is, don't run the motor and take it to a performance tuner shop to check all this out. My personal thoughts is that you have a sensor or programming problem. If you are consistently running lean ratios from idle to WOT, it's probably electrical. Pull a plug(s) out first to see, to be on the safe side. Hope this helps,zrxlover.
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Old 12-18-2009, 09:09 PM
Lignite Lignite is offline
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Thanks for the tips. I'm a bit worried about my wideband O2 sensors as well (2 of them, other 2 postcat sensors are eliminated in the ECM tune) but from reading up on them and some bumbling testing I think(?) that the O2's are functioning correctly.

I haven't made much progress yet, as I've had some major breakdowns in the interim (swapped out 7.5" rear end for 8.8", chevy rear springs, front wheel bearings, Warn Jeep hubs, brakes, all in my yard and its been COLD).

But, before the breakdowns, I decided that the miss was getting worse, and that I may (or may not) be wrong about the A/F not richening. I think now (but can't confirm until I get back on the road) that the reason I'm not richening under boost is that the engine is not actually 'getting wound up' (or approaching WOT) before I get spooked and let off because of the missing. So while it is dangerous that I'm not getting more fuel, I'm not pushing the motor very hard (chickening out) because of the miss, and never get close enought to WOT to throw more fuel in. So if I can find whats causing the miss, I think it might fix my A/F problem.

Among the other things I've changed since starting this thread, I have switched the DPFE (no better). I did get new plug wires, but don't believe the old ones are bad (aftermarket 8mm motorcrafts) so haven't installed them. I have also installed a new pair of aftermarket coils, but can't test them until I get the front and rear ends together (soon I hope!?!)

Thank you again for the advice.

P.S. checked 2 plugs some time ago, looked good to me (but I'm far from an expert). I also got a scanner, but haven't learned how to read what I'm seeing yet (no codes thrown).

Last edited by Lignite; 12-18-2009 at 09:23 PM. Reason: corrections and additions
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Old 12-18-2009, 10:03 PM
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I'd definitely change all the plugs. Sometimes the insulator can develop cracks, and have a direct short to ground.

Hopefully the new coils, wires and plugs will fix the miss. If it doesn't, then you should start looking at your fuel injectors.
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Old 12-18-2009, 10:53 PM
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Plugs are all new, and since I have them I guess I should just buckle down and put the wires on too (it is SO tight in there), but the motorcrafts on it now appear very new. I know I know, just change them

Gawd I hope it ain't fuel injectors, I intended to check them with the stethescope trick, but I'm apparently not smart enough to do that. I forgot to mention I did get a fuel pressure gauge, and all appears well, although I could only test while stationary.
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Old 12-18-2009, 11:41 PM
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Quote:
Originally Posted by Lignite View Post
Thanks for the tips. I'm a bit worried about my wideband O2 sensors as well (2 of them, other 2 postcat sensors are eliminated in the ECM tune) but from reading up on them and some bumbling testing I think(?) that the O2's are functioning correctly.

I haven't made much progress yet, as I've had some major breakdowns in the interim (swapped out 7.5" rear end for 8.8", chevy rear springs, front wheel bearings, Warn Jeep hubs, brakes, all in my yard and its been COLD).

But, before the breakdowns, I decided that the miss was getting worse, and that I may (or may not) be wrong about the A/F not richening. I think now (but can't confirm until I get back on the road) that the reason I'm not richening under boost is that the engine is not actually 'getting wound up' (or approaching WOT) before I get spooked and let off because of the missing. So while it is dangerous that I'm not getting more fuel, I'm not pushing the motor very hard (chickening out) because of the miss, and never get close enought to WOT to throw more fuel in. So if I can find whats causing the miss, I think it might fix my A/F problem.

Among the other things I've changed since starting this thread, I have switched the DPFE (no better). I did get new plug wires, but don't believe the old ones are bad (aftermarket 8mm motorcrafts) so haven't installed them. I have also installed a new pair of aftermarket coils, but can't test them until I get the front and rear ends together (soon I hope!?!)

Thank you again for the advice.

P.S. checked 2 plugs some time ago, looked good to me (but I'm far from an expert). I also got a scanner, but haven't learned how to read what I'm seeing yet (no codes thrown).
I'm not sure but,I thought that the turbo(boost) A\F ratio,o2,fuel delivery were supposed to work together at all levels of boost? Why do you have to be at WOT before it richen the fuel mixture? If they don't work together all the time: boost, A\F,O2 shouldn't your ratios be off all the time? I could be wrong but, I don't understand a system that doesn't adjust A\F ratios.O2 and fuel delivery through idle to WOT? Why only at WOT, help me understand, please? As far as your two plugs. You can buy a colored plug chart that will tell you what they supposed to look like and what they don't supposed to look like and a explanation why they are that way. Most service manuals like Haynes and Chiltons have colored plug charts in them. I'm not sure but, I still think you have a sensor problem? Just my thoughts,zrxlover. I hope you figure it out before it ruins your motor!!!
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Old 12-19-2009, 11:03 PM
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You say the ECU was reflashed, do have a handheld or was it flashed by a tuner? I wouldn't worry about the O2's that much since that signal is negated in open loop fueling.

How does it idle and are you running a bypass valve?
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Old 12-20-2009, 11:45 AM
Lignite Lignite is offline
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Sniper Special Forces tuner (software and flash box as I understand it). Truck was idling good, and even better now with new coils (Screamin Demon). Running a blow-off valve to atmosphere (but with the manual trans I am thinking the bypass system would be more useful?).

And for ZRX, I think I said that wrong. My understanding of the Explorer PCM (please correct me if I'm wrong!) is it uses three fuel tables, low medium and high power. I believe my tune is set up to use about stock fuel table for low power, start adding more fuel in the medium table, and really dumping fuel in the high table. I was told this is done for fuel economy's sake. It does add more fuel for boost conditions, but not as much as for high power boost conditions. This is probably oversimplified, as I don't know if I completely understand all of the PCM parameters that were modified to add more fuel, but it does (or was) working quite well according to the A/F and boost gauges before my problem developed. I'm thinking the 'miss' is not allowing the PCM to utilize the high power fuel table, and therefor I'm not seeing the safer (lower) A/F ratios I need to in boost. Just my theory, so far all my theories have been wrong!

I got new rearend under it and front wheel bearings in and took it for a drive today, but no bed, no 4 wheel drive and no brakes (wrong front gear ratio and brakes need a bleed) and its snowy everywhere here, so I can't get enough traction to even get into boost yet.

I'm hopeful that the new coils may have fixed my problem, it seems to be running very healthy, but I need to finish my drivetrain overhaul before I dare to really get into higher horsepower stuff. Whew, got a little long winded there. sorry.
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Old 12-20-2009, 11:45 AM
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