Needing Help!!! Engine is cutting out and missing like crazy!!!!

97 Tacoma 4cyl, 5 speed, 4x4.

I have been trying for days now to take notes on the consistency of this miss.

It is a Part Throttle miss. It never misses at idle and has yet to miss at Wide Open Throttle. Its consistently Part throttle, uphill with a load, downhill with no load. It misses when the engine is cold and at operating temp. It misses in the rain as well as dry. No climate makes it miss more or less. Speed is not a factor either. The truck is NOT throwing a check engine code.

Now this miss is best described as this.... Drive down the road at whatever speed. 5mph to 85 mph. Reach up and click the ignition key off then right back on... Thats what I am dealing with. The only difference is when I click the key, my gauges drop and warning lights come on. The miss does not alter any of that stuff.

This will last from a fraction of a second to a couple seconds. A few times not I had to push the clutch in and start the truck again. In those cases it fires right back up and takes off time. Its not hesitating like it running out of fuel. It runs fine then out of nowhere it misses. On my 47 miles each way drive to work it will do this anywhere from 10 to 50 times.


Now, things I have changed helping to narrow it down....

Now fuel tank (old one was rusty anyhow)
New fuel pump/gauge unit
New fuel filler neck
New gas cap
New fuel pump
New fuel pressure valve on fuel rail
New fuel pump relay
New used fuel pump wiring harness

New plugs
new wires
new coil packs

New ignition switch


I am drawing a BLANK!!!!!! Can anyone give me some insight????

 

alternator or vacuum leak or injectors....???

 

I was wondering about injectors as well.... but they are ALL cutting out. its just like clicking the key off and back on.

Alternator is making juice right, new battery.

I have looked for vacuum leaks, but I have not found any. You can not hear any air hissing anywhere under the hood.

 

The relay I changed is the one under the dash (near steering column) that the shop manual said was the fuel pump relay.


Would that be different from the EFI relay? Where is the EFI Relay? fuse box under the hood? Any idea how to test it?

 

Check all your grounding wires, bad grounds can make for intermittent problems.

Did you scan it or are you just going by the fact the light isn't on? There are some codes that won't show the light right away.

From all that you have already done, symptoms point to a vacuum leak, possibly the throttle body/intake manifold gasket.

 

I have a nice OBD I & II scanner. It brings up no codes, nor is the light on.

I rebuilt this truck from parts. Would you happen to know where all the grounds are? Maybe I am missing one? The truck was not missing like this in the beginning when I started driving it.

I have tried the spray test on the intake and the trucks idle does not change.

 

spray test??

 

Fuel line bent?

 

RPM can be 1,500 to 6,000. makes no difference... only thing that matters is throttle position. To the floor and it never misses...



As for the bent fuel line... no, I checked it when I was having other issues. No bends.

 

ahh k gotcha, just never heard that called a spray test

 

when you changed out all those parts in the fuel system did you change the fuel filter? that would be the first thing I would have changed.

 

Mass Air Flow Sensor?????

 

yes, changed. Possible its a bad filter? Wouldn't a filter cause more of a spitting and sputtering hesitation miss rather than just it cutting off totally???

That should throw a Check engine code. Too much $$$ in it now for another guess.

I know how to test that, but I have no idea what the actual test is.

 

Easiest thing to do is go buy MAF Cleaner at Autozone or Pepboys and spray the internal part. Mine went twice on my '99. First time I replaced it, second time I cleaned it.

 

Throttle position sensor? If it had a distrubutor id say ignition module but that's ruled out.

 

Took the advise of a few and tried the TPS. It was a $58 gamble that I was unsure of since the check engine light was not coming on, and no codes in the computer. I have an appointment at the local Toyota dealer for Wednesday to get it checked out ($80 hr).

I changed the TPS last night... Drove the truck about 60 miles or so since... Not a single stutter.... I am going to have to guess it was the TPS and it is now fixed.... Thanks everyone.