I've posted about this issue in various other threads, but I've yet to figure it out and keep checking out more and more things, so I figured i'd start a dedicated thread and post my findings (and hopefully eventually the solution) here.

in short, its a problem described by the PO when I bought the truck that it will just lose power randomly while driving. it didn't to it to me for a could of weeks, but now started doing it pretty regularly, but only when the truck is warmed up, it seems. also, there is no rough running or anything when it happens. its really just like the engine doesn't know that i'm stepping on the pedal to go faster.

here's what's done/tested/monitored with my scangauge so far
- the PO changed the MAP sensor and MAP tube. I've confirmed that the MAP tube is clear as well as the bung in the manifold. I've also quickly checked for boost leaks in the manifold and turbo, but will inspect further in the future if I can't figure this out otherwise. after the PO changed the MAP with no luck, he says a buddy of his told him it must be a bad PCM. i'm skeptical of that, but who knows...
- before/after buying the truck, I went over the standard things and found that the ICP was bad (oil in the connector), so I replaced it with new - no change
- ICP and IPR duty cycle are both in line with each other and both read accurate to engine speed rather than pedal position - i.e. IPR DC is not through the roof try to get ICP up. ICP never usually exceeds 30%, and IPR has no problem hitting 3000+ when the issue is not occurring
- MAP reading is inline with engine speed and power output, not pedal position.
- intake air temp reads normal and accurate
- trans gear seems to be aligned with engine speed - for about a day, I was thinking that maybe the trans was just shifting too soon and bogging the engine down - the PO replaced the tranny and I thought he (or Jasper) could have screwed something up wiring wise. just curious - is this possible? I have tried dropping it down into neutral, then back to D or down into 2nd gear while driving, but this doesn't seem to change anything.
- EBPV and EBP sensor. I've unplugged the EBPV and the problem still persists. my EBP scangauge reading is pretty steady at ~15-19 psi even while driving. I've had expected this to be higher under load, but wasn't sure. I do get good boost pressure when the problem is not occurring and I hear lots of turbo whistle out of my straightpipe exhaust. when the problem is happening, the whistle doesn't go away, telling me that the EPBV is probably not closing off.

my next things i'm suspicious of are:
- the Accelerator Position Sensor - since the truck seems like it doesn't know I want it to go fast sometimes, this seems like a logical potential problem. occasionally, but not all the time, when its doing this power loss thing, if I stomp the pedal all the way to the floor, the truck will downshift and take-off like it should, which makes me thing of a go-pedal issue, but i'm sure this could point to something else as well.
- BARO sensor - I believe the PCM compares the MAP against the BARO to determine actual boost, so if the BARO is reading too high, that would cause the PCM to think the boost is low and scale back on fueling right? perhaps related to this - my Wait To Start light goes off very fast (like in 1 second) no matter if the truck is hot or cold - though admittedly, I've only driven the truck in july/august, so maybe it stays on longer in the winter. in my other truck, it would stay on at least a few seconds even on the hottest days in the summer, though. not that I can see how GPs would factor into this, but by looking at the voltmeter, the GPR does stay on longer than the 1 second WTS duration...

ok, any thoughts or input are much appreciated.

Thanks!

 

ok, i'm just doing some reading in my links I have stored. just came across this regarding the EBPV:

" If this system is rendered inoperative in the open position, it isn’t much of a problem, but in some cases, the oil piston that drives it (by way of a PCM controlled solenoid) can receive oil through a bad solenoid and close the butterfly when it isn’t supposed to. This causes a low power concern."

anyone ever have this happen? I guess this is the argument for wiring the valve open in addition to unplugging it... but again, I still get good (same as with no problem) turbo whistle when the problem occurs. not that this is a definite that the valve isn't closing, but i'd think you'd hear it less...

 

...just found an old post I was looking for: https://www.ford-trucks.com/forums/1...nsor-info.html

reading through this points me to the BARO sensor again. I assume the BARO is the same as the MAP, in that if I unplug it, the PCM will take it out of the loop and use some default value?

also, is the absolute pressure reading on my scangauge a BARO reading, or MAP reading? or is it that the boost reading is the difference of the two sensors with the MAP reading being absolute pressure and BARO being ambient?

 

Set 1 channel on the scan gauge to monitor EBP. When the issue occurs see if the back pressure is normal ~ 15 - 19 PSI. That will eliminate a few problematic areas.

MAP measures boost where BARO measures atmospheric (altitude) pressure. The PCM uses BARO to know what altitude you are at to fuel correctly. On start up the PCM compares BARO to MAP which should be the same value ( within a few PSI) when the key is first turned ON. If not the PCM disables BARO, set the CEL and uses MAP as the default altitude indicator.

In another post you indicated when this issue occurs the RPM's go up but the speed does not? To me that sounds like the transmission is slipping ... but maybe I read it wrong.

WTS light sound OK for summer months. It is a simple function of IAT and EOT and if both of those reading look OK I wouldn't worry about it.

 

My vote is for the Acc position sensor. My 97 would randomly not respond to the go peddle, but if I would let my foot slip off the peddle, and let it bang back to the idle position, it would then work like it should. A transplant of the foot feed from my parts truck solved the problem.

 

that's right, and i'm kind of thinking the same thing, maybe - which would be fine by me as its still under warranty from Jasper, for at least a short time, and I plan to swap it to a ZF5 anyway. i would do the swap, send back the trans, and then try to sell the new one... i would like to eliminate most other problems, though before going and making that claim. would an improper installation cause a slipping trans, or is it necessarily internal to the trans itself?

if the trans was slipping, though - wouldn't the RPM's go to the rev limiter, though? that's definitely not happening. or is there a partial slip that could be happening.

a question related to this, though - when the problem happens, my boost is quite low - like 1-2 psi even at high RPMs. i know that a load on the engine is needed to build boost, so would a slipping trans, drop the boost this much? normally, at the same RPMs, i'd see 10-15 psi.

i'll have to try that. i have another OBS PSD, so i'm thinking of testing out this pedal and putting into that other truck to see if the same thing happens there...

 

Boost is, of course, the amount of air crammed into the cylinders. If you have ever watched EBP values on cold mornings, and the valve operating properly, the back pressure can get up to 43 PSI when the valve closes. The computer is constantly adjusting the valve position depending on engine load. As back pressure goes up boost goes down. Anything above +25 PSI back pressure and your boost goes to zero, from my observations.

That is why I suggested watching EBP as the problem is occurring to determine if it's a exhaust type problem ... or not.

I'm not an transmission expert so can't answer that question. I would think if the transmission is slipping the boost would go down as there is less load on the engine.

 

OK, i'm still dealing with this power loss problem. I thought I had it licked (again) over the weekend, but it came back this morning on the way to work. over the weekend I checked my Throttle Position Sensor and found it was not behaving as it should. the pedal on my other truck tested out good, so I swapped that one in and took it for a drive. throttle response was much better and power was through the roof - it was like a brand new truck.

then, on the way in to work this morning, the same old power loss problem came back. same symptoms as before - low power (with low boost).

i'm pretty convinced its not the tranny slipping it doesn't seem to be excessive EBP, as that never goes above 19 psi. also, looking at Boost vs. MAP Absolute, the relationship seems to be correct at all times, so I think that rules out the BARO sensor.

moving on down the line, i'm thinking I should get a look at fuel pressure under load. I would have thought the engine would run rougher during these problems if fuel was an issue, but I suppose I should make sure its OK. the truck idles fine and pressure is good at idle, but i'm thinking i'll want to rig up a fuel pressure gauge to check under load.

can anyone recommend a good electronic sending unit? I figure i'll buck up for the sending unit now and hook up a permanent gauge and mount it in the cab later. for now, I think I can just run it through one of the analogue input connections on my scanguage. any advice or how-to's on this would be appreciated.

another thought I've had regarding this problem is possibly low voltage coming out of the IDM. when this issues occurs, the truck really does behave as if it just doesn't know it want it to accelerate fast (or at all), then sometimes the power will kick back in all of a sudden and sometimes the problem is gone for days at a time, so it has all the annoying symptoms of an electronic issue. has anyone ever had (or heard of) an IDM losing power/voltage across all injectors? I have 2 other IDM's I could try, but I don't just want to throw them in knowing that it could be a wiring issue that may have caused issues with this one in the first place. I know there is a test procedure out there to verify that each injector circuit is working properly (i.e. not shorted or open) before just replacing an IDM.

well, first things first, I guess - i'll check the fuel pressure and then go from there.

EDIT: I just opened the fuel filter bowl at lunch today figuring if its starved of fuel from the tanks/bowl the level would be low there as the problem was still happening when I pulled into work this morning. the bowl was full to the top and the filter and fuel were clean, so no issues there. ...maybe still low fuel pressure, though.

 

ok - anyone use this sender? the price is right and glowshift is a decent name, I think...

Replacement 0-100 PSI Fuel Pressure Sensor

looks like you just supply Vref and feed the output into the aeroforce interceptor analogue input and it should work, right?

seems that all fuel pressure gauges use the same 1/8" NPT thread as well, so i'm guessing it'll fit.

EDIT: nevermind - that one seems to connect through the ground side of a traditional analogue gauge - not sure how the scaling would work out in supplying 5V through it to the scanguage. The AF scangauge wants a 0-5V signal input - i imagine i could figure out how to make it work, but it would take some effort and tinkering - and finding a convenient 5V power source under the hood. taking the easy way out, luckily AF carries a sender on their website - $65 is more than $16, but hopefully there shouldn't be any issues getting it to work.

Should be here by week's end - lets see what this tells me now...

 

ok - i'm just copy and pasting this post from another tranny-specific post i had going on this power loss issue, but long story short - i think i have the problem solved. i'll still install that gauge for kicks, but it turned out to the the trany connector as the power-loss culprit.

-------------------------
OK - just wanted to close up this thread for anyone reading it in the future. i'm 99% sure that the improperly seated trans connector (on the passenger side) was the problem all along. after getting it cleaned out and seated properly last week, i had it on several long drives this weekend without any hint of the power-loss issue coming back and the trans still shifting better than it ever has since I've owned it.

with this identified as the problem, and looking back on the symptoms, i would say it seems one or more of the connectors controlling the shift and TC lock solenoids were just not engaging at all, or sometimes at random. i remember at times wondering if i really had 3.55 gears in the rear like the door sticker said, since i'd be cruising at 50-60mph, but the RPMs were up over 2k. i guess the TC was just not locking at those times. then, the bogging down that i'd get at low speeds sometimes was probably the trans being in too high a gear or locking up the TC when it should not have. and all the while, the PCM had no idea what was going, so no check engine and no OD light flashing.

anyway, glad i got it fixed - now onto the fun projects with the truck!

 

Wow, sounds like you may have found the issue. You just cleaned it and put it back together? Thanks for this info. I could see this being extremely frustrating. BTW JP, did you see my post of the TPS/IVS issue I resolved? If not, check it out. It might be worth reading for you. Cheers!

 

thanks Byron - i did see the post, but didn't get a chance to read yet.

and yeah, i can't see this trans connector issue being a real common one, but i'm guessing it happened when this previous own did his own tranny replacement and didn't have the connector lined up right before jamming it home. it probably worked fine for him for a while until it got some dirt in there and the connections started going bad.

then he tried some other fixes, not thinking his brand new tranny would be the problem, then gave up and sold it...

 

Score for you!!

 

exactly..............