98 V6 Wont rev over 3500 - Detailed

[HelpMeFixIt]

We have replaced the following -

Fuel Filter
Fuel Pump
Removed Cat
Cleaned MAF (new one was tested some time ago, no change)
Cleaned throttle body etc
New plugs
New coil packs and wires
New timing belt, water pump and tensioners - keyway looked fine...
New crank position sensor
Cam position sensor was tested OK
Computer swapped

I think thats it and truck still acts the same. Runs extremely smooth to about 3500 then feels like its hitting limp mode, but computer swap did nothing either.
Not the neutral safety as it wont crank in Drive.

I started a new thread so I could actually detail what we've done. I've read many threads about the issue and nothing seems to be resolving it.
Looking for any input as to next steps we might take.

Thinking now to check/replace TPS, but not sure on that one. We can at least test it with a meter though.

Any help is GREATLY appreciated.

Scott

 

[0xfded]

The first question anyone is going to ask is "have you checked the codes?"

Any NAPA or Pepboys place will loan you the reader for a few minutes to check.

 

[Sierra946]

Did you check solenoids in transmission? If one of those goes bad, it will start in 3rd then shift to fourth pretty much not allowing you to ever get your rpm's up. Ask me how I know this

 

[HelpMeFixIt]

The first question anyone is going to ask is "have you checked the codes?"

Any NAPA or Pepboys place will loan you the reader for a few minutes to check.

Yes and there are nor have been any codes at all.

 

[HelpMeFixIt]

Did you check solenoids in transmission? If one of those goes bad, it will start in 3rd then shift to fourth pretty much not allowing you to ever get your rpm's up. Ask me how I know this

Details? What solenoids would I be looking for? Location?
You're saying in park, it's actually starting in 3rd?
When we drive it, it behaves the same as in park.

Also, as I mentioned above, there is no code and never has been since this problem first started.
So not sure it would be a tranny solenoid.

 

[LittleCaesar]

Unless you have the ability to keep buying parts for some time, I'd at least get a scanner that reads live data. See if something goes amiss at 3500 rpms and higher.

Did you check the fuel pressure regulator?

 

[HelpMeFixIt]

Unless you have the ability to keep buying parts for some time, I'd at least get a scanner that reads live data. See if something goes amiss at 3500 rpms and higher.

Did you check the fuel pressure regulator?

We didnt mind buying what we have so far because we paid $500 for the truck and it has 270k on it. It really needed all of this stuff anyway

Fuel pressure was just checked and according to the info my dad found, its high at 46psi dropping to 40psi when turned off. Info states it should be 38psi at idle and 21psi turned off so we're investigating this further.

Also, the injectors were professionally cleaned by witchunter.com.

Our immediate next course of action is the fuel pressure regulator and the throttle position sensor (test with meter).

Would HIGH fuel pressure cause this condition? A safety of some sort coming into play?

 

[LittleCaesar]

For that amount of money, I'd throw parts at it too.

Just pull off the vacuum hose off the FPR after driving it. If it smells like gas, or some trickles out, then the FPR may be bad, though I have yet to hear of one going south.

Was this a Denso fuel pump or another brand?

Too much gas could be a bad thing. Does the crankcase smell of gas after driving it? Is it hard to start afterwards?

 

[HelpMeFixIt]

For that amount of money, I'd throw parts at it too.

Just pull off the vacuum hose off the FPR after driving it. If it smells like gas, or some trickles out, then the FPR may be bad, though I have yet to hear of one going south.

Was this a Denso fuel pump or another brand?

Too much gas could be a bad thing. Does the crankcase smell of gas after driving it? Is it hard to start afterwards?

Not sure of fuel pump brand, but it helped the most with smoothness up to the 3500 after we replaced it.

Nothing smells of gas after it runs.

FPR vacuum line was actually plugged when we got the truck and my dad hooked it back up.

Latest update... He tested the TPS with a meter and no dead spots.
Tested fuel pressure with gauges and was at 46psi under load till it hit 3500rpm. 40psi at idle.

Tested MAF with meter and also had expected results.

Is there any way to test a FPR? I need to google and youtube that

This is really starting to aggravate us for obvious reasons. What seems to be just about everything has been tested or replaced and nothing is resolving the problem.

O2 sensor couldnt cause this could it? Is there a way to test? (google and youtube )

 

[LittleCaesar]

Every FPR check I have performed involved making sure that pressure was in the acceptable range via a fuel gauge and more important is to have working pressure held for at least 5 minutes or whatever the allotted time is after the key is turned off before it is returned to the tank.

I'd suspect the MAF, but if it tests good, then the numbers won't lie. My buddy's mom had a squirrel once eat into but not through some wires leading up to the MAF in her Maxima so give that a cursory look as well.

 

[HelpMeFixIt]

Update...

Phone a friend, previous ASE Master... He came by then called his cousin who is the shop foreman at a local Toyota dealership. He came by.
Bottom line seems to be exhaust related. No codes ever for this problem. Cat was removed but muffler wasnt.
No time tonight so testing will continue tomorrow. Crossing fingers it's the dang muffler.

He said in so many words, that what we're experiencing is too much exhaust pressure.

 

[LittleCaesar]

That could do it for sure. I assumed you weren't running the muffler as well. Another time an assumption kicks me in the rear.

Let us know how it turns out.

 

[HelpMeFixIt]

Dropped exhaust and same thing.

 

[HelpMeFixIt]

Bump..... We seriously need help with this :-(

 

[HelpMeFixIt]

Back to the top... Any help or advice would be greatly appreciated.

 

[Srabai]

Have you checked the knock sensor?

Not sure if this'll help with the solenoid thing.

Tip - FAIL SAFE MODE
Fail safe mode is enabled whenever #1 or #2 shift solenoids fail electrically. In addition, PCM will disable lockup solenoid. If either solenoid or its circuit is shorted, PCM stops sending Control signal to it until fault is corrected. Fail safe shift patterns are as follows:

#1 SOL fails..."d" position= 3rd
#2 SOL fails..."d" position= 1ST
#1 SOL fails..."2" position= 3rd only
#2 SOL fails..."2" position= o/d
#1 SOL fails..."l" position= 3rd
#2 SOL fails..."l" position= 1ST only

Let us know what you figure out.

 

[HelpMeFixIt]

Have you checked the knock sensor?

Not sure if this'll help with the solenoid thing.

Tip - FAIL SAFE MODE
Fail safe mode is enabled whenever #1 or #2 shift solenoids fail electrically. In addition, PCM will disable lockup solenoid. If either solenoid or its circuit is shorted, PCM stops sending Control signal to it until fault is corrected. Fail safe shift patterns are as follows:

#1 SOL fails..."d" position= 3rd
#2 SOL fails..."d" position= 1ST
#1 SOL fails..."2" position= 3rd only
#2 SOL fails..."2" position= o/d
#1 SOL fails..."l" position= 3rd
#2 SOL fails..."l" position= 1ST only

Let us know what you figure out.

Will check into the knock sensor.

Not sure tranny solenoids are an issue. This issue occurs in Drive, Neutral and driving gears.
We havent tested all driving gears, just a short drive around the block.

 

[HelpMeFixIt]

Thoughts on my latest theory....

Floating valve?

 

[JohnMc]

The only times I've had similar issues it was exhaust back pressure. Once it was a melted and plugged cat, once it was an internally collapsed muffler.

Obviously that isn't the case here.

The thing that is befuddling me is that you've already replaced every thing I'd suspect of causing an issue.

If you drive it around, does it have a normal amount of power under that RPM? Does it pull cleanly and firmly from idle in gear?

Is the fizzle rpm pretty much the same when driving vs. in neutral? If so, that would seem to indicate that air and gas flow isn't the issue, but something more like a sensor if failing, or cam timing or ignition timing is seriously off.

 

[HelpMeFixIt]

Cam sensor was tested with a meter but never replaced.
I just ordered a used one from eBay for 40. Can't hurt and it's warrantied.