Long story short, bought the van for cheap, it wasn’t working well enough to drive( had to tow it to my house just to work on it) . As a little hobby I pulled and rebuilt engine, installed reman. transmission. I drove it for 2k miles, seemed to work alright, until on the highway building up speed to merge on (drove on highway before no issue). The whole van started to shake and it felt like I had no real power, wouldn’t get above like 50ish and sounded realll high rpm’s for nothing. After this I kept having issues with higher speeds/ hills it felt like it would slip out of gear and “neutral” let go of gas and go slower to make it the rest of the way. Transmission company sent me out new transmission and TC, installed, still having same issues, replaced all transmission harness sensors just in case (no codes this entire time to help) still didn’t change. Fluid level is good at hot temp, it drives good for about 20 miles and then seems the issues start popping up with neutralling or slipping. Replaced spark plugs and coils, (had already been changed just a shot in the wind I had cheap coils on) still same issue. Last time i drove it i came to a stop sign, as i took off i felt it shift to 2nd and it “neutral” slipped again but this time the whole vehicle shut off, no flashing lights or anything just turned off, i pulled over and restarted and limped the rest of the way about 30min. I’m thinking maybe ECU issue? I can’t see how it’s the transmission if the second transmission has same symptoms, possible engine issue? Since it popped up so suddenly with no codes I was wondering if it’s ECU issue, I ordered a junkyard ECU same model and code number exact replacement, maybe it’ll run different. Any ideas?

 

Are you using the same MLPS, neutral safety sw ?

Are you sure it is being adjusted correctly?
If certain solenoids are not getting signals certain things cannot work correctly.

 

I replaced the NSS when I did the transmission sensor harness “blitz”. I’ll double check the positioning I believe I have the two small lines lined up in neutral, I’ll check again and get back. I may have found a possible issue, the dipstick tube wasn’t fully pushed in so the “ring” wasnt flush with the transmission, so my fluid level may have been off from what it should have been. Which makes sense to me now that I think about it, the transmission started giving issues after about 20 miles or so basically a warm up, but that doesn’t explain the original one blowing up after 2k miles, unless it’s just coincidence, I guess I didn’t pay attention to the dipstick tube the second time of pulling that darn transmission

 

Well I adjusted the dipstick tube and measured the amount of fluid I took out when I did, and I ended up putting about the same amount of fluid back in I believe, after moderate warmup the dipstick is right around half way on the hot side(12 miles, when i do cold check on level ground, i have engine running cycle through all gears, check fluid and have cold level just above minimum cold level) so fluid is good I believe. I drove it 12 miles and shifted through all gears great, drove 60 mph and everything, but right at 13 miles up a hill the transmission started slipping and staying in low gears, no warning lights, continued this way until parking. Fluid was halfway on hot side, so fluid level isn’t an issue I don’t believe, and once again it’s a remanufactured transmission, the second one. First one lasted 2k miles great then started the slipping issue and I believed it was transmission, and so did company so they sent me another one, installed it and still have slipping issues. So it shouldn’t be the transmission, so like I was thinking…maybe it’s ecu, I’ll put a used one in and see, I’ll give updates.( The NSS small lines were lined up when in neutral)

 

Another update, swapped ECU with junkyard one, drove 12 miles, didn’t have to program ECU everything ran fine. Until warm up like usual, issues started again. I believe it might be the catalytic converter after further forum searching, the converter can cause issues after warmup and sometimes not throw codes, which is my situation, can’t go above 45-50MPH on flat roads after warmup and can’t go up hills 20-30mph.( I believe the slipping i get when trying to push the engine might just be the engine limiting itself or it just can’t “breathe”.)Which is basically the same symptom as a clogged catalytic converter. I got a back pressure gauge and tested cold running pressure is normal, will test hot running pressure and check back.

 

Don't forget to check the intake system for any restriction, can provide similar symptoms.

Where did you connect the gauge to test for back pressure? Vacuum gauge? If so how did you check it ?

 

Well I finally figured it out! I tested the back pressure with a back pressure gauge in the O2 sensor port before the catalytic converter, this was reading normal while hot, so that’s not the issue, so thinking about what hanky said I looked at intake, the air filter was new already, but I’ve yet to look at or change the MAF, I figured if it was the MAF a code would have been set? I’ve gotten no codes this entire time, I pulled the MAF, the first probe looks just slightly dusty, but the second probe is like completely black, to me maybe some kind of oil got on it then got burnt from heating up? I know the previous owner said he had to spray starter fluid just to get the engine started previously, possibly the oils from starter fluid? I’m not sure, I’ll post a picture. Swapped the MAF with a new one, I’ve drove it 27 miles and no issue, drove it 55mph up hills no hesitation/stalling/slipping. Hopefully this thread may help someone in the future… check your MAF! Even if there’s no codes…it could still be the MAF. I hate that I swapped out a good reman transmission but it was leaking in two spots (one was the fluid pump seal so it would have to be pulled anyways) so it was good I no longer have one that’s leaking. But all is well.

 

Well it drove great for a month, then issues came right back, weird? Engine stalls/ bucks under load. I thought the new MAF sensor fixed the issue, because everything stopped after replacing it and been driving it for a month no issues until it just started again today, I tried changing the TPS with old one, that didn’t help, unplugged the MAF, that didn’t help, unplugged the vacuum on the fuel regulator and that helped some? Able to go to about 50MPH under some load, still have issue, going to check fuel pressure, I understand the fuel filter and fuel pump is new from previous owner but maybe faulty cheap pump? Engine stalling like I’m having under load makes me think it’s fuel related, since new plugs and refurb injectors.. thinking delivery is issue, catalytic converter is not issue

 

Well my fuel pressure is measuring 28 psi at cold idle, I believe I might know why the van worked for awhile, I had been keeping the fuel tank full and I just let it get below half a tank when the issues started, maybe that let the fuel issue show itself with less gas in the tank to cool the pump, it could have been a coincidence when i changed the MAF sensor i had filled the gas too before the issues started, I didn’t really want to drop the gas tank and I found on YouTube people figured out how to locate the fuel pump from inside and cut an access panel for it. The previous owner told me the fuel pump and filter had been changed when I bought it…the filter looks new but I’m not too sure about the fuel pump yet until I open it up. It could possibly be just a cheap fuel pump going out fast. I never had issues with cranking, only issues under load, possibly just a weak pump, I’m going to replace the fuel pump and fuel filter with both motorcraft brand, will keep updated

 

What does the pressure show when you increase engine speed to around approx. 2500 RPM ?