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MikeWild
02-16-2009, 12:10 PM
I'm stumped, I just completed a 2.9 to 4.0L swap into my 91 5spd ranger. Everything seemed to work fine once I fired it up and did a test drive with it yesterday. Yesterday, I drove about 10 blocks to the store, everything was fine. Coming home, it all went south. Here's the symptoms:

Starts fine
Idles fine

As soon as I go to give it gas, the RPM's jump up and down like I'm pumping the throttle. I thought it might be the IAC valve, so I unplugged it and it just stalled out. I thought maybe there was a ground wire issue as my negative cable looks like poo so I cleaned it all up. No effect. Checked the ground wires at the ECM, and they look fine. Today I went and played around a bit more, checked the vacuum lines, MAF, all look good. I don't suspect a faulty fuel pump or filter as the truck drove fine with the 2.9 prior to pulling it. I also don't suspect the 4.0 ECM as I also drove it without issue prior to yanking the 4.0. Out of 10 fires, it ran and revved perfectly as though nothing was wrong one time after completely shutting the truck off, then it went back to messing with me.

I noticed today when farting around with it, that as soon as I brought the RPM's up to around 2000 is when it started it's revving up and down routine, but if I kept it under 2000, I could shift through all the gears and get the truck somewhat up to speed.

I'm suspecting a possible TPS issue, but would appreciate any insight you all might have in solving this issue.

Thanks[cheers]

epic3
02-16-2009, 12:23 PM
fuel pump still the one from the 2.9 Im assuming.
thats where Id start it probably cant maintain pressureésupply for the bigger engine

dirka dave
02-16-2009, 12:25 PM
Engine light on ?
Is it OBD I or II ?

MikeWild
02-16-2009, 12:34 PM
No CEL, I'm pretty sure it's OBD I as OBD II is 96 and newer. The fuel pump should be ok from what I've read up on these swaps. If the fuel pump was suspect, I highly doubt it would run like a champ on the infrequent times it chooses to. My test drive also consisted of hill climbing and such and it was perfect.

A6D9
02-17-2009, 06:17 AM
once warmed up in neutral when yuo rev it aboe the 2000 does it still do it?

my GF's old honda did that...and it turned out to be an air buble in the coolant system?

I'm no mecanic..but figured I'd offer that bit...her car ran fine some times others times not...

Vastier
02-17-2009, 08:33 AM
I'd go with the TPS or more likely the MAP sensor.
A faulty MAP sensor on the 2.5 L jeep engines will give all the same symptoms you're seeing.

Troy
02-17-2009, 12:20 PM
tps or fuel pump

dirka dave
02-17-2009, 12:25 PM
Loose nut behind the wheel ??


:dontknow:

C.W.
02-17-2009, 12:32 PM
Already seen some good places to start, im not going to repeat. One other thing i learnt is fords need their ground straps from engine-body as well as body-frame. How many of each do you have?
Usually most i have seen have atleast 3 from engine to body and 2 body to frame. Also anywhere the harness was grounded to the frame or body in the vehicle the 4.0l came from find a way to ground your current harness.
Good luck, electrical and computer related issues are frustrating.

Troy
02-17-2009, 12:35 PM
Already seen some good places to start, im not going to repeat. One other thing i learnt is fords need their ground straps from engine-body as well as body-frame. How many of each do you have?
Usually most i have seen have atleast 3 from engine to body and 2 body to frame. Also anywhere the harness was grounded to the frame or body in the vehicle the 4.0l came from find a way to ground your current harness.
Good luck, electrical and computer related issues are frustrating.

very frustrating

degsey
02-17-2009, 12:41 PM
buy a chev that would be a good start

MikeWild
02-17-2009, 04:55 PM
buy a chev that would be a good start

quit flapping yer lips....... an even better start! :D

thanks for the helpful tips guys, I've given up on figuring it out until I return from my vacation.

thrillbilly
02-22-2009, 07:32 AM
i appogize in advance if i missed somethin, but without reading any posts here my guess is idle air control valve.
had that get clogged up on my integra way back, and on my s10 and it caused the loping rpm
you can disconnect your filter housing from the intake mani and spray brake clean into the IACV while keepin rpms up to clean it out.

*should* solve the hunting rpm

MikeWild
03-07-2009, 03:27 PM
finally figured out the problem today. Turns out it was a faulty CPS. She runs like a champ now! Thanks for the tips folks

bigrig81
03-08-2009, 09:16 AM
cps? i know tps, but not cps..... ???

MikeWild
03-08-2009, 12:05 PM
crankshaft position sensor

Faulty CPS
http://i155.photobucket.com/albums/s316/dawebpics/6.jpg

Working CPS
http://i155.photobucket.com/albums/s316/dawebpics/A.jpg

bigrig81
03-08-2009, 01:07 PM
lol, the print out prett much show's the story hey! hhaa thanks!

nbrowser
03-08-2009, 02:33 PM
CPS = Crank Position Sensor, most EFI engines got one and some even have cam position sensors too. Helps to time the injection and in all distributorless motors, the spark timing is run off it too.

Nice Computer run DSO Mike....I likey, can you give info about it ?

MikeWild
03-10-2009, 07:57 PM
info? Like on the unit itself? It's off of a genisys spx

http://genisysotc.com/

curlee
03-10-2009, 08:09 PM
I totally thought this was something about erotica.. my mistake...

Zibi
03-10-2009, 09:23 PM
my nissan will do the same thing when it's cold and sat for a couple days, friend whos a nissan tech suspected it was the MAF wacking out. I'm too dumb to know if that might be the same thing with your motor.

thrillbilly
03-11-2009, 03:13 AM
my truck does this occasionally. did it in mcdonalds drivethru today.. was at about 700rpm then surged to 1100 and back down. i blipped throttle and it was fine.

MikeWild
03-11-2009, 10:53 AM
my truck does this occasionally. did it in mcdonalds drivethru today.. was at about 700rpm then surged to 1100 and back down. i blipped throttle and it was fine.

If the RPM's don't drop all the way down to zero & then back up again, it's probably not the CPS, it might be the IAC (idle air control) or a dirty MAF[cheers]

Troy
03-11-2009, 11:13 AM
my stupid ranger always surges like that too if it sits for a few days or when cold. previous owner couldn't figure it out but usually after it warms up its fine.

thrillbilly
03-11-2009, 02:09 PM
yeah i think its the cold effectin somethin cause it usally never surges at all.
and mikewild nope it never drops down below idle just surges up to around a thou.

im hopin its just IACV gonna take off air filter pipin and clean'er out.

degsey
03-11-2009, 02:10 PM
its not the cold its a ford

thrillbilly
03-11-2009, 02:50 PM
at least its not in a junkyard like most chevs! :p just kiddin but ya i had the same problem on my 2.9 ranger damn fords