Wont rev over 1500, 2000,2500, or 3000 RPMS

[Big-E]

Hey all,
97 XLT 4.0 SOHC 4 x 2 - 183,000 miles

This am it was dumping rain in TampaBay Florida and my truck didnt want to go over around 1500 rpms. As i turned around to go home I hit a puddle and it got a bit better. Hit the gas and she ran up to 3k no issues then stopped. I know i have a sensor issue. On the drive to work it would cycle between reving out to 2000,2500, or 3000 rpms when ever it wanted to. This is in gear under load so it should not hit a limiter but it seems it's runing in limp mode. I do have the check engine light on but I think its due to bad intake gasket (slated to change vavle cover gaskets this weekend and intake gaskets.

I have owned this truck for the last 120,000 miles and this is the 2nd time this has happened. The 1st time i replaced the CAS sensor and it corrected it. I am thinking this could be AFM or TPS.

Any ideas?

Also if anyone would like to take a stab at it, since about 95,000 miles the O/D light will flash on and off on the dash in random. Hit a bump.. it will flash.. then stop 10 mins or whenever it wants later. Had tranny serviced around 100,000 k per the manuel.

Thanks Again,

Eric

 

[2000StreetRod]

read the DTCs

Since the Check Engine light is on I suggest that you read the diagnostic trouble codes before replacing anything. I keep an inexpensive reader with my vehicle so I can read and clear any codes when they happen.

The crankshaft position sensor location exposes it to road water and grime. Sometimes disconnecting and connecting the electrical connector cleans the contacts. The PCM uses the MAF sensor output to determine engine load. You may want to spray the element with a MAF sensor cleaner aerosol.

The transmission fault could be from a poor electrical connection or short aggravated by a bump. I've learned that the 5R55E is sensitive to a low fluid level.

 

[Big-E]

Sweet thanks. Codes ecu is putting out is lean bank left and right I belive. I have already replaced all the O2 sensors - Gas milage isnt perfect and its very inconsistant. Some tanks its 12.5 mpg's and others I get as much as 19.9 - in the middle of chasing this down.

So on these motors the crank shaft pos sensor is the one that gives the ECU input on what the motors doing? I am assuming if i unplugged it the motor would go into limp mode and max out at 2000 rpms?

The tranny issues def sounds like a short...I tried looking for it once and never found it, tranny fluid level is perfect via stick once its warmed up.

You did give me a direction to go in, looks like cleaning the crankshaft sensor should be priority 1.

Thanks again,

Eric

 

[2000StreetRod]

lean codes & crank sensor

The lean codes are probably due to leaking upper and lower intake manifold gaskets if they've never been replaced.

I doubt the engine will start or run with the crankshaft position sensor disconnected. The PCM will disable the fuel pump with no crank sensor signal.

You may want to test the throttle position sensor: TPS Test Procedure

 

[Big-E]

nice, thanks for the info. I'll post my results tonight once i get home.

Yes I have never replaced the upper and lower intake gaskets..well.. this weekend i will..

Eric

 

[Big-E]

UPDATE****

My 30 mile trip home = no issues. Truck ran just like it should, This leads me to believe some sensor got wet that affects some sort of spark cut off. I did remove the crank sensor elec connection and clean it, took down the MAF and cleaned it, checked the TPS.. it was perfect per the link posted (.95 shut, 4.66 wide open) and giving good numbers between. Took down TB and IAC and gave them a good cleaning to. Had battery disconnected to clear codes and she fired right up.. Sounds and runs really good but exhaust smells rich (prolly why gas mileage last tank was 12.5).

I am really stumped on why I had this issue in the rain (2nd time in about 10 yrs of ownership). Thanks for the links they helped! If anyone has any other ideas let me know.

Thanks,

Eric