Can't rev over 4000 and won't accelerate
 

Hi,

My car does not want to run over 1/2 throttle and I can not get my engine to accelerate to over 4000 rpm no matter how long I let it try. It seems to run fine at low throttle positions around town, but it has no guts.

This may or may not have been triggered by a failed alternator that was sparking and throwing spikes. I believe it may have been acting up before the alternator.

I've checked all vacuum lines, fuel pressure seems to hold when I rev it in park.

I have checked my exhaust backpressure previously and found it never really was over 1 psi. Now it is 1.5 psi at idle and rises to 4 psi when I rev it up to 4-5K.

I have hooker headers, 3" y-pipe, original stock cat with 110K, and Magnaflow exhaust.

The books say not to worry unless the backpressure is over 8 to 10 psi.

Anyone else have a good running engine with similar backpressure readings. Does this sound like convertor problems or should I look for something else.

Fuel, ignition, timing are next.

:(

Sounds like your cats are plugged. 8-10 psi?!?!?!? There shouldn't be that much back pressure at all! I have like no back pressure since I'm catless and my mufflers are quiet.

Yep. I agree.
I would put my money on it being the centre cat taking a trip south.
I remember reading once that cats are likely to last around 50k...if yours is still original, well.....!

Sounds like a clogged cat. Take it up to 3 grand and floor it, If it sounds like there are a bunch of marbles bouncing around in the engine your cat is done for and needs to be gutted out or replaced with a test pipe.-Mike

When my cat got clogged, first I could only go 70 mph then it was down to 40 mph. I reamed that thing out, and it was flying better then ever.

Dave

Oh yea, I think any more than like 4 psi and you have some kind of obstruction in your exhaust. Cat may not be your problem, but mine went around 110k-115k miles mainly due to a bad MAF.

get the magnaflow cat this time, and do not buy from madvet.com.

magnaflow is the one.

:iagree:

I know exactly what is wrong with your car, You have a stock L98! :rofl:
Sorry guys I just couldnt resist! L98 :boxing LT1
(Just Funnin)
Roy

:iagree: Been there. Exact same symptoms. You car will run like a scalded dog once you replace your cats.

I had a similar problem about a year ago... turned out to be a bad / shorted injector...

It could also be something as simple as the fuel filter needs changing........I had this on another vehicle with the same issue described

My friends car just had the same problem and after replacing the fuel filter and changing the cats it ended up being the Mass Air.

A quick way to check if it is the Mass Air is to disconnect the plug from it and then the computer will go into limp home mode. My buddies car was throwing no codes and right after he pulled the plug on the Mass Air it revved right up.

It might not be the Mass Air on yours but my friend wished he looked there first before messing with the fuel filter and cats.

Do you have the stock injectors in your 89? The injectors can be easily tested for shorted coils. Let us know if you need more info on the test method.

I had a similar problem.. I couldnt rev it above 3k or so and It turned out to be bad injectors.. also my cap/rotor were burnt...

it finally died and wouldnt start agian..

c4 not revving
 

I know this post is old but what fixed it? I have same deal.

Well i just pulled timing cover off. This thing went thru 3 people that i'm assuming couldn't figure it out. It was off three teeth. Someone put it at 0 advance then lined the keyway up with the can gear dot. I thought I would post this if someone has same problem. Three teeth off apparently it won't rev over 4000 rpm