2000 Chevy 3500 5.7L wont go past 1500 RPM

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Thomas1190

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Feb 16, 2010
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Palmdale, CA
Hey guys, my truck is trippin out. Its been like this for a year and a half and I finally decided to get it running again. The reason I bought my Sentra . When I start the truck it starts nice and quick and idles smooth at around 1000 RPM then once warm to about 750. If I slowly give it gas it wont go past 1500 RPM and starts coughin and choking. Its poppin(backfiring? Sounds like a rattle in the exhaust) and shaking at 1500 RPM. Now if step on the gas all the way itll go way past 1500 but runs like total [censored]. It all happened after i was making a turn at a stop sign. I punched the gas (to feel that awesome V8 power lol) the RPM were definetely up in the high range and then all of a sudden i slowed down, had a loss of power and couldnt get it to go past 1500 RPM and had to crawl home. The CEL was on. Today i took off all the intake pipng and cleaned the MAF with some CRC MAF cleaner. Then I unplugged the battery and let it sit for a couple hours to reset the ECU. Plugged it back up started it and the problem is still there although the CEL is not on anymore. I have no idea what it could be now. Maybe i just need a whole new MAF? I got a feeling its got to be some type of sensor b/c it idles totally fine until i give it gas.I have heard it could be a bad MAF, O2 sensor, or a vacuum leak. Anybody ever had a similar problem, any ideas? Whenever i get time i plan on taking it to a local mechanic and have him hook it up to the computer to see if it will say what the problem is. Just wanted to see if this problem sounds familiar to anyone before i take it. Im 19 and a college student working part time so money is kind of tight. I hope i can get everything worked out for no more than $300(hopefully that doesnt sound too crazy lol). Thats the most i can spend at a time. The truck has 204,000 miles BTW
shocked2.gif
Thanks in advance.

New parts that were put on a year and a half ago before the problem
distributor and cap and rotor
spark plugs, plug wires
fuel pump
 
I would guess you have a clogged catalytic converter. A vaccuum gauge can show restrictive exhaust.
 
Wait, I beleive mechanicx is correct, you have a rattling in the exhaust thats usually a dead giveaway for a catalytic, atleast everytime I have had to get a new one it has rattled.
 
Converters don't clog then unclog. If you were able to get up to higher rpms with power then I would lean towards sensor of some kind. The code that was in the computer before you erased it would have helped alittle. Of course a problem like this is difficult over the internet to diagnose.

If the problem is consistant (lack of power), I would first drive with MAF unplugged. If most/all power returns then MAF is bad. Otherwise check fuel pressure as another thing to check.
 
If all checks well, then loosen the exhaust Y-pipe at manifolds. If this takes care of all your problems then cat(s) is/are clogged.
 
So i was doing some research on the internet and it seems that there could be so many different things thats causing it to go in "limp mode". Eventhough the engine light is not on anymore, because i unplugged the battery for a couple hours(maybe that was a bad idea), the codes that caused it to come on in the first place should still be stored in the computer right?
 
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No, they are gone. Its possible codes are there, but have not turned on the light. These are pending codes and it will take a few cycles for them to become actual codes.
 
I'm not nearly as knowledgeable as others on here, but my first guess when reading that was something with the vacuum lines. But again, I'm not as knowledgeable as others on here.

If I were you I'd pop the hood with the engine off and cool, and look for the white sticker/label that shows the emission control info. It should show you a simple image of the vacuum lines on your engine. Use the info to find the vacuum lines, you don't have to remove them (and if you do remove and work on them one at a time), but follow it from end to end as best you can with your fingers to make sure everything is connected and there are no cracks or other signs of clogging or wear. Similarly, make sure no caps that might have been sealing an opening haven't fallen off.

After that, with the hood up, start the car and let it idle, go back and try to listen if you hear any air suction or blowing noises.

While it might not be a vacuum issue, it sounds similar to the problem I had on my SUV where after changing the PCV valve I didn't realize I had knocked off a little cap. I also suggest this b/c it's something that can easily be done without cost whenever you have a little bit of time for it
 
No way it's a cat... the truck would still run fine at any RPM, (especially an OBDII engine)it just might run rich.

My dodge just towed 4,000 pounds from NC to OR with a 'catalyst inefficiency' code and a 'slow response' code from the rear 02. (the failed 02 killed the catalyst in the converter due to a rich mixture) Ran like a champ, just used a little more gas.

Next time, don't clear the CEL, check it! Borrow a scanner from Autozone.

I think it's ignition/fuel related. But you need to find out what the actual code(s) is/are.

Best of luck.
 
There's different kinds of cat failures. There's efficiency failure and there's physical damage/restriction failures. A lot of GM cats had restriction failures around that time frame, ~2000-2002. I've seen it several times and his symptoms are of a restrictive exhaust, i.e, engine runs smooth but won't rev.
 
Originally Posted By: defektes
Since hes in the GREAT state of california it is illegal for him to borrow a code scanner from a auto store.
Are you serious?
 
The cat is the failure point for sure. My 2001 Impala had a failed cat, would literally sputter and feel like it was going to die. I thought at first it was teh trans, because no matter how much gas I gave it, the engine would feel like it has power to an extent but the car wouldn't go past like 20mph.

If the truck is under 80k miles, you can have it fixed for free as the Cat is an 80k warranty item. No time limit.
 
Originally Posted By: genynnc
No way it's a cat... the truck would still run fine at any RPM, (especially an OBDII engine)it just might run rich.

My dodge just towed 4,000 pounds from NC to OR with a 'catalyst inefficiency' code and a 'slow response' code from the rear 02. (the failed 02 killed the catalyst in the converter due to a rich mixture) Ran like a champ, just used a little more gas.

Next time, don't clear the CEL, check it! Borrow a scanner from Autozone.

I think it's ignition/fuel related. But you need to find out what the actual code(s) is/are.



Best of luck.

I disagree, when the honey comb starts coming apart it will clog the cat and cause high backpressure. This is exactly what has happened and why he has a rattle in the exhaust. It's a bad cat!!
 
Originally Posted By: xxch4osxx
Originally Posted By: defektes
Since hes in the GREAT state of california it is illegal for him to borrow a code scanner from a auto store.
Are you serious?


yes
 
Originally Posted By: Anies
If the truck is under 80k miles, you can have it fixed for free as the Cat is an 80k warranty item. No time limit.


Its got 204,000, just a hair over lol.

I never would of guessed a Cat failure. Seems a lot of you think thats the problem. We'll see once i get time to take it to the shop. From now on i am never going to clear a CEL when i "think" the problem is fixed. We all learn from mistakes, this one of them. And yeah we cant borrow an OBD2 scanner. Either we take it in and have a tech look it up or we have to buy our own, and those things are pretty pricey.
 
Got another question. Becuase I live in a small community out of town, the closest repair shops are about 15 miles away. Is it ok for me to drive it that far while going a slow speed, assuming its a cat problem?
 
If your going under the speed limit by a lot, the police can ticket you. Especially the CHP, wow you live in palmdale, your not very far from me hah.
 
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