[slu.ridge]

Hey guys,
The tacometer doesnt seem to work on my 2007 truck. Sometimes it idles at 3000rpms, sometimes the tacometer dont work. Now the truck doesnt rev past 4000 rpms. Anytime it gets there it starves. Its like the truck is in safe mode. Driving up hills is a problem the truck goes up very slowly in second. I have a chk light on and the scanner says o2 sensors.

Anyone had similar issues? Thanks for any information as to what should ido

 

[skelley521]

Looks like it's all over the place.... idles 3k then tac doesn't work then won't rev past 4k.
Have you done any work recently?
At night when it's running does the catalytic converter/s look red?
I have seen this issue before on several cars, just can't come to a conclusion without more info.
It does sound like its in limp mode, which can be issues with several items that send info to the ecu/ecm or a faulty ecu/ecm.

The O2 sensor would lead me to a bad sensor or plugged cat just for starters.

 

[Dnick]

My advice is if you have the check engine light on, pay for a quick diagnostic.... or at the VERY least, get the codes read to be sure you aren't damaging something further by continuing to drive it! (presuming there's something more to this than O2 sensors, which I suspect there is)

I agree tht checking the cat is a good place to start too.... blocked exhaust is not a good thing, and can potentially get you some burned valves eventually. If you're inclined & can pull it off (& are where you can get away with the noise), try disconnecting the muffler &/or rear cat (I'm thinking it bolts up - don't remember off hand) just for grins to see if you can get your "above 4K" performance back. That would confirm the blockage theory.

..... but I'd save myself some trouble & start with a good diagnostic. (but keep in mind that sometimes you only get "chase-your-tail" results from that as well .... like misinterpreting O2 & cat issues)

 

[chiph]

Agree. If the O2 sensors needed replacing a long time ago, the catalyst might now be clogged, which would put the engine into limp mode. Like skelley521 says - if the cat is cherry red -- you've got a major problem.

Check the codes, investigate what they tell you.

Chip H.

 

[slu.ridge]

I have the truck 2 months now
The previous owner had a clogged cat which they decatted and changed the primary o2 sensors which is those on the exhaust manifold
I havnt done anything except change oil
The truck starts and idles with no issue. On the instrument cluster the temp doest work and the tacometer needles goes crazy
The truck upshifts and down shifts nicely
It just doesnt rev past 4000rpm and dont climb hills. Its like 4k rpm is redline and the fuel cuts off

 

[slu.ridge]

I scanned it today and the error code was primary and secondary o2 sensors
My mechanic check all with his multimeter and they were fine

 

[skelley521]

Has the truck been running good since you bought it and these issues just showed up recently or has it been doing it since purchase?
Have you tried disconnecting the battery for a bit to see if the ecu resets itself?

 

[S.T.U.V]

I have the truck 2 months now
The previous owner had a clogged cat which they decatted and changed the primary o2 sensors which is those on the exhaust manifold

Like they removed the inside of the cat? That will cause problems.

 

[slu.ridge]

It has been doing that since i bought it, but the previous owner said it was the clogged cat and had it resolved but it never did.
I think they took off the cat split it open took off the inside and welded it back

 

[slu.ridge]

Another thing the longer the drive the worst it gets
All be doing a long drive tomorrw evening
Ill look out for glowing exhaust parts

 

[skelley521]

It's up to you if you trust the work was done.

I said the cat was plugged as the symptoms you described indicate it as a probable cause.

Check it at "Night" to see if anything under there or the engine compartment is red.
Also look for any small sparks while you're under the hood also.

Also have the battery tested for voltage & amperage. Look for the battery date to see when it was installed or due for a change.

You said the temp gauge isn't working, the manual should be able to trouble shoot that.
I'll look at it and get back to you.
Also you stated the tac jumps around? Is it a constant bouncing situation or is it a "working fine one minute then jumps around for a bit but goes back to normal function later"?

 

[slu.ridge]

The battery is fine
The tacometer works fine now then when i switch off it will stay on 3k rpm. So yes fine now then crazy next minute. That kinna thing
When the scanner was plugged in the mechanic said the taco needle, speedo needle, fuel and temp needle was suppose to move from min to max then back to min but it never happened

 

[speedlever]

That is incorrect. I've seen GM cars sweep the gauge doing a check when you first turn the ignition switch on. The RL does not do that.

I can't tell from your description if the engine is following the tach needle or if the tach is jumping around independent of the engine rpms itself.

I hate to say it, but it sure sounds like you bought someone else's problem child.

Edit: how do you know your battery is fine? Erratic instrument indications are often a symptom of a failing battery.

 

[Carsmak]

This Vehicle eats batteries, unless you just changed it, that's where I'd Start. You need to identity if this is in the instrument cluster or the engine. If/when you can get a scan tool, such as "Scanguage" or "UltraGuage" or any of the Bluetooth OBD2 and a Android Based Smartphone or Tablet, running the Torque App. Then you can get confirmation the "throttle" is stuck or the computer has it in a safe mode. If it's in the "cluster" a forum member rebuilt his instrument cluster, by changing "stepper motors"

Speedo Repair, by Replacing Stepper Motor

 

[Dnick]

You have only reinforced my thinking that you need to rule out a clogged exhaust. It's possible that previous "clogging" put debris farther downstream in your exhaust... could be now in muffler or rear cat.

The point is, you need to rule out clogged exhaust. Excessive backpressure could easily cause your symptoms. IF this is your problem, it's a straight forward, if not cheap/easy solution to fix. Just overhaul your exhaust system with new cats/muffler, and your good to go.

As for your tach.... this seems to me to be a completely independent problem that needs to be separately addressed as a "next on the list" problem. Your immediate concern should be to not ruin your engine ..... FIX whatever is limiting your power output, because it 'could' be causing you further damage. You'll just kick yourself later if you fart around until the damage is already done.

 

[slu.ridge]

The taco needle moves independent from the engine idle

If all fingers point to clogged cats ill have them checked out again. Makes sense might be clogged lower doown the exhaust system.

Thanks guys for the information. Will let you know whats up.

 

[NSXer]

I am curious about what is the effect of a bad rpm sensor? If the meter itself is okay but is not getting the correct values from the sensor. Readings on the meter would be inconsistent + I would assume the ECU will react on this misinformation.

I am no expert on a fault like this, so hopefully someone will chime in and enlighten us.

No offense, but how do yoou know your engine is stalling at 4000 rpms when the meter is not to be trusted?

I do hope you solve this problem soon.

 

[slu.ridge]

When the taco needle is in sync with the engine it doesn't go past 4k

When its out of sync it does the same.

 

[OwnerCS]

This reminds me of an issue I had with another Japanese V6 that experienced clogged cats. The car was extremely hard to start. It didn't want to run. It would die and wouldn't restart. I had the car at the dealer and they told me it needed a new engine. The engine only had 75,000 miles and I knew they were full of it.

So I had the car towed from the dealer to my house and decided that I would be fixing it. It took all of about 20 minutes to pull the upper O2 sensors (I left them hooked up BTW) so the engine could breathe once I started it. It was loud but it started up and ran like a scalded dog. Pulling the upper O2 sensors was a quick way to determine that I had exhaust blockage.

I had to pay the dealer $700 and a towing charge to get the car home so I could fix it. I guess you can see why I generally have a distrust of dealer service departments.

 

[speedlever]

What causes a clogged cat? Is it fuel related?