HELP! Engine will not rev past ~ 2200 RPM...

Hey guys!

I did try to search through old posts and didn't see anything similar to what I am experiencing. I hope you can help me out here. I have a problem that my car will not rev past about 2200-2500 RPM.

A mechanic friend of mine and I have checked the spark that comes thru the wires with a snap-on tool - it's reading very low "kb's" according to him.

Thinking it ignition related and was possibly related to the distributor, I swapped it out... no change. Cap/rotor are new. Thinking it was plugs, we swapped them out - no change. Thinking it was the coil I swapped that out - no change.

With a scan tool connected, the O2 sensor is a bit 'lazy' but it is doing it's job. At idle, the car runs fine and bounces between rich/lean. TPS volts look good. Brand new map sensor since I broke mine reassembling the intake.

It starts fine (actually VERY easy) Only when I bring the RPM up it wil go rich and around 2200 is bogs down. Car does die, just won't ramp up any faster RPM. It's blowing grey smoke (not black and not white).

The car has new accel 8mm wires. I used to have a LT4 hot cam and TFS 23* heads but the car never ran quite right...so I've put it back stock save for an ait pump delete and hedman hedders. The EGR is in place, but disconnected. I checked this to make sure it was sealing properly - it was.

Two things I have yet to check are the vacuum and the compression ratio. Car has over 100k on stock engine. My friend indicated that low CR can cause low KB's on the wires since there is more resistance in the plug 'arc' in the cylinder (presumably from a poor air/fuel compression = less volitile mixture). I could also have a vacuum leak somewhere - but why would it kick in only at higher RPM?

Of course, I suppose the new plug wires could be crappy too...

Any other suggestions? I feel like I just keep throwing money at the problem... I'd like some pointers - maybe someone on here has had the problem before.


Thanks in advance...

Richard

The catalytic converter might be plugged.

Originally posted by Sitting Bull
The catalytic converter might be plugged.



^ What he said.

Didn't think of that...but wouldn't that affect it at idle too? How about the KV's on the wires? It is something to check though, thanks!

A pluged exhaust may not cause a problem at idle because the engine does not have to expell as much exhaust from the cylenders as it does at high RPMs. My guess would be a plugged cat or other exhaust component. As far as the low voltage in the secondary ignition....it could be a lot of things. If the primary coil is fine, the dist is new and your high tension leads are in good shape you should have good voltage.

Disconnect the cat from the Y pipe and try to rev it on open manfiolds, if it revs up, you found the problem.

Good luck,
Erik

Originally posted by Scrote
A pluged exhaust may not cause a problem at idle because the engine does not have to expell as much exhaust from the cylenders as it does at high RPMs. My guess would be a plugged cat or other exhaust component.

OK, I just bounced this off my mechanic. He didn't seem to think this would be the case - in his experience the car would still run even at high revs - it just wouldn't have any power...

Since it's easy to drop the Y off the hedders, I'll still check it..just wanted to relay that info. The other thing is that if it had a clogged cat, wouldn't it be muffled better? Its pretty darn loud and seems to push plenty of air out the exhaust.

As far as the low voltage in the secondary ignition....it could be a lot of things. If the primary coil is fine, the dist is new and your high tension leads are in good shape you should have good voltage.

Why is the tem 'high tention leads' not ringing a bell? How can I check this?

Is it possible for new accel plug wires to have too much resistance? I'm gonna try swapping the old wires back on since I still have them to rule this out.

Disconnect the cat from the Y pipe and try to rev it on open manfiolds, if it revs up, you found the problem.
Neighbors are going to LOVE me! :D

Originally posted by gun4hire
OK, I just bounced this off my mechanic. He didn't seem to think this would be the case - in his experience the car would still run even at high revs - it just wouldn't have any power...





If your cat is plugged bad enough, you will not be able to rev it high. How would it be able to high rev if it couldnt get rid of the exhaust fast enough if it was clogged?

Originally posted by IROCThe5.7L
If your cat is plugged bad enough, you will not be able to rev it high. How would it be able to high rev if it couldnt get rid of the exhaust fast enough if it was clogged?

True, but would it just happen all by itself? Car has been run off/on but mostly sitting over the past 6 mos. What also makes me wonder is that it is still rich and I get plenty of rich exhaust...not like it's just barely puffing or whatever...

I'll still check the cats, but I dunno.... :confused:

is there any way to check the cat without taking the exhaust apart? I'm having the same problem where the car bogs at 2200-2500 rpm's, but mine only does this occasionally.

Rally Sport yours sound like a fuel pump starting to go bad.
I have seen alot of bad cat converters over the years. They will bogg the engine down to the point of stalling under load. They will idle fine. They will run very rich. If you had a injector bleeding down and the car sat for 6 months that would do it. It would cause alot of back pressure in the engine and load the engine up. In turn that would coat the plugs. Pull a plug and see it it is wet.

Originally posted by Chris Ja
In turn that would coat the plugs. Pull a plug and see it it is wet.

In my case, the plugs are fouling - but not to the point of being wet. I will add that when I had the LT4 HOT, LT1 intake and TFS 23* heads that the plugs would be wet when I was troubleshooting. One of the reasons I got fed up with that and am going back stock.

Thanks for the added info!

I hope this isn't a fuel pump problem because I just replaced it this fall and it cost a lot of $$$$
So if I pull the plugs and it isn't wet, what do you think it is?
I just put in a Jet Stage 2 chip and now problems are happening, but they don't happen all the time. With the chip in, my cars performance has been way better, but then occasionally she tries to die. Im afraid if I put the stock chip back in im going to get crappy performance again.

you could pull out the O2 sensor if you do not want to drop the exhaust.
but dropping the exhaust is the best idea.
HAVE YOU CHECKED YOU AIR FILTER(S)?????????????????

Originally posted by stevem
HAVE YOU CHECKED YOU AIR FILTER(S)?????????????????

Since I have speed density (no MAF) this happens even with the throttle breathing open air.

:eek: O2 sensor is as bad as dropping the exhaust IMO... :D

I'll updateyou guys once I have tried this..

Originally posted by gun4hire
Why is the tem 'high tention leads' not ringing a bell? How can I check this? Scrote means "Spark Plug Wires"...he's a mechanic, he uses technical terms.;)

Eric

Sorry man, a High tension Lead is a spark plug wire.

As far as dropping the exhaust...yeah it can be a pain with out heat, impacts, and a lift, but it is probably the best way to check it....but before you do it try this.

Hit the cat with a dead blow rubber mallet if **** rattles around in there than you have found your problem as the catalist has heated up and melted down snd broken apart causing the clog in the system.

Let me tell you times like this a DVOM can be a life saver, as you can test stuff and not have to load up the 870 express with parts and "shotgun" parts at the car. :)

Good luck bro
Erik

Originally posted by Scrote
Sorry man, a High tension Lead is a spark plug wire.

As far as dropping the exhaust...yeah it can be a pain with out heat, impacts, and a lift, but it is probably the best way to check it....but before you do it try this.

Hit the cat with a dead blow rubber mallet if **** rattles around in there than you have found your problem as the catalist has heated up and melted down snd broken apart causing the clog in the system.

Not sure 'bout the other guy, but I just reattached theexhaust 2 weeks ago when I put the car back stock - so the 3 bolts will sill be easy to separate.

Let me tell you times like this a DVOM can be a life saver, as you can test stuff and not have to load up the 870 express with parts and "shotgun" parts at the car. :)

Huh? Easy for you to say! :p

Digital VOlt Meter. I work on cars all day every day and I agree that they can save a LOT of hassle if you know how to use them.

Welp, I have an update.

I picked up a vaccuum guage and hooked it up to the tube for the power brakes. Ran the car and once warm it pulled about 14-15 inches...fairly steady.

Then I ran the RPM up a bit and as it went up, the needle went down. Once I hit the spot where the RPM will not go up anymore, the needle had hit almost zero. The book that came with the guage indicated that if this happens, the likely culprit is a partially blocked muffler or cat converter.

I smiled thinking this confirmed what folks on here thought. :)

I put the car up on ramps and dropped the Y-pipe off the headers (the dual cats and the Y pipe are all connected solidly). it only gave me about 1/2" from the bottom of the hedders to the Y-pipe flange. I ran it (briefly because it was 10pm) and it did the SAME THING!!! :mad:

I also bought a compression tester, but didn't have time to mess w/it any more.

Any more ideas? This one's a REAL headscratcher for me... :confused:

Exact same thing happened to my bonneville. started poking around and found a vacuum line that was cracked in half/sheared (it was metal).

The car would rev up to 2500 and spit and sputter until it died.

Make certain that ALL vacuum lines are not only attached BUT also are not damaged/leaking/broken!

I dunno man, a 1/2 inch might not be enough of a drop, just pull the y pipe off the car and out of the way. If you still have a problem with the hesitation, if it where me I would check valve timing next.

Pop of the rocker arm covers and check/re time he rocker arms. I would run the car with the covers off, and then back off each individual rocker arm until it "clatters" and then tighten slowly untill you hear the noise stop, then tighten 1/4 turn. You might be experiancing some valve float and this might take care of it. Also when the rocker arm covers are off, make a good visual inspection and make sure that everything is looking good, no broken valve springs and such.

Good luck, it is hard to diagnose drivability problems over the net ;) so hopefully it all works out for ya,
Erik

Originally posted by RedIrocZ-28
Make certain that ALL vacuum lines are not only attached BUT also are not damaged/leaking/broken!

I will double check, but I JUST put the intake back on - all the hoses/tubing appeared fine at that time.

I spoke to my friend and he's going to check a system he has with vacuum readings and possible solutions... Initially, he's thinking I may have lined the camshaft up incorrectly. :(

We will see...

Originally posted by Scrote
I dunno man, a 1/2 inch might not be enough of a drop, just pull the y pipe off the car and out of the way. If you still have a problem with the hesitation, if it where me I would check valve timing next. I would have hoped that I would have seen some difference, right?Pop of the rocker arm covers and check/re time he rocker arms. I would run the car with the covers off, and then back off each individual rocker arm until it "clatters" and then tighten slowly untill you hear the noise stop, then tighten 1/4 turn. You might be experiancing some valve float and this might take care of it. Also when the rocker arm covers are off, make a good visual inspection and make sure that everything is looking good, no broken valve springs and such. Hopefully, springs will be fine. I just had the heads worked, and I'd be upset if the shop screwed something up. What is odd to me is that if it were just a couple exhaust valves without the proper preload, I'd expect the vacuum to bounce around. I'd say it was fairly steady - even as it dropped off at higher RPM. I think that's why my friend is thinking cam timing since that would affect all the valves at the same time.

Good luck, it is hard to diagnose drivability problems over the net ;) so hopefully it all works out for ya,
Erik I REALLY appreciate all you guys trying to help me out. Thanks again! :)

I have found the problem over the weekend...

The three-way timing set I have has provisions for 4* advance/retard and straight up. It is adjusted in the install of the crank sprocket. This was installed correctly.

The problem is in the indicators (and the fact this is only the 3rd time I've installed a cam). They are a triangle, a square and a circle (just so happens to be adjacent to the cam timing 'circle'.. Guess what? Yep, I had simply used the wrong one! This resulted in the cam being quite a bit advanced...thus the intake/exhaust valves were open when they weren't supposed to be. I am SO fortunate to have done this with a stock cam, as one with more lift would have smacked the valves into the pistons.

So anyway, thanks to everyone here that has helped out... Even though this was a problem, I have learned A LOT in solving it.

Ahhh ha, so it was valve timing....in a round about way ;).

Congrats man, its always nice to have your car back and running...

Peace,
Erik