I have a '91 camaro with a stock 3.1 that has about 137k miles on it.

It has recently developed a problem that I can describe as the higher the rpm the crappier the motor runs. For example, going down the highway at 65 mph it seems to run ok (but not as much power as I think it used to have) but if I floor the pedal it will downshifts and rpms increase to about 4500 rpm and the engine (hesitates?). Another example, If I accelerate hard from a stop ther motor pulls decently to about 4-5k rpm then runs like crap. I'm not talking about the general lack of power at higher rpms that these engines have. The motor at high rpm runs real rough and I feel like it might stall if I kept forcing it to run like this.

Any ideas what my problem could be?

Note: The fuel pump and most ignition components were replaced last summer. The timing chain, catalyitic converter, fuel injectors, oxygen sensor, and many other parts are still original.

 

137k id replace the timing chain, it may/may not have anything to do with your problem but its kinda old with all those miles.

A car i used to have acted the same way your car is now. Turned out the cat was clogged.

 

yeah, i'd look into the cat, then the ignition coil and then the pickup in the dist.

clogged cat will make it sound like it's constipated

a weak coil won't be able to hang with the shorter dwell time

and a bad pickup might get a great signal at lower RPMs, but gets all confuddled up higher

 

That 02 sensor should have been replaced roughly 65,000 ago... Need a coil? I have two!

 

Check the pickup coil... actually, just yank the distributor, and rebuild it. It's cheap to do, and your 2.8 will thank you!

I'm throwing my vote for clogged cat, as well.

 

If your cat is clogged, first try removing (take it right off) the O2 sensor and take it for a drive. If you notice a huge improvement, that means the exhaust finally has an escape route.

 

i doubt that removing the O2 is going to make a difference. The size of the hole with the amount of exhaust that actully passes there isn't going to show any real gains if the cat isn't totlly clogged. If it's partially cogged then all he'll accomplish is sending a searing hot jet of exhaust out the bung, plus now you run the risk of running so rich that it just bogs because of that.

 

I have to disagree with you since I speak from experience. My cat was clogged pretty bad and when the O2 sensor was out and it's hole was open it ran way better. I've also driven without the O2 sensor a separate time and it ran a little rich, but better.

I do see what you are saying about partially or totally clogged though. But if it's clogged enough to make a very noticeable loss in power then power will noticeably increase when the sensor's out (it won't be great, but it will be better).

 

Thanks for the responses so far.

Here's some of the ignition work I've already done -

Pickup Coil - 9000 miles ago
Distrib Cap & Rotor - 9000 miles ago
Ignition Module - 11000 miles ago
Ignition Coil (MSD Blaster) - 19000 miles ago
Ignition Wires - 19000 miles ago
Spark Plugs - 19000 miles ago

So, I'm guessing the ignition system should be in decent shape. I didn't realize I had 19k on the spark plugs. I guess I should at least pull them and take a look. BTW - How long should a set of plugs last in these engines?

I've been planning on replacing the oxygen sensor sometime soon. And, a timing chain is on my list of things to do but I generally need to drive this car every day.

Is there any easy way to "test" a catalytic converter? I had an old Crown Vic that had the cat plug up so bad that it got cherry red after running the car for a few minutes. How else can you tell if the cat is bad? I have to assume that replacing it wouldn't be bad at 137k miles but I'd hate to think it would fix my problem and not.

Also, what would be the symptoms to a problem with a fuel injector?

I appreciate the help.

 

If you had a problem with a fuel injector, then you would have a noticable misfire, think of pulling a plug wire and running like that. Now you may have freakin' filthy injectors, but that all depends on the gas you run/have run in the past. I don't know how clean the gas is in your area, but out here in cali. they are **** about "clean" gas. if you have stuff in there that can make deposits by running it through a daily driver...it's too dirty for California. As long as the fuel doesn't sit and varnish, they should be fairly clean. My car has 217K on it and has never had the injectors cleaned, not to say it wouldn't help generally, but slightly dirty injectors won't kill power so much that you can tell the difference between high and low RPM drains. If they're dirty, they'll perform crappy no matter where you are in the RPM range.

If you step on the gas does it sound like an old man trying to crap out a watermelon...if so, you have a clogged exhaust. You might not notice it so much in park/neutral, but you can hear it when you're under load...say 2nd & 3rd gear acceleration.

only real way to see if you have a clogged cat is to take it off and look through it. Mine collapsed because I had one hell of a misfire about 3 months ago. It broke into chunks and part of it slid down the I-pipe and I had to fish it out with a drain snake. Now it's empty.

Try listening to it, that's the best shot other than tearing it off.

 

It seems reasonable to assume that my cat might have crapped out on me and that was my first guess as to my problem. I guess I'm gonna have to pull it off. I might throw a straight pipe in its place to take it for a test drive and see what happens.

Anyway ... thanks for the help.

 

So could a clogged cat cause an engine shake or vibration? (noticeable shake at idle and definite vibe after 3000rpm).

 

If the cat is clogged, most the time it appears after a certain "run time" the backpressure builds and does not let exhaust gas flow.

Mine had that problem sparatically for a while.
I checked the gaps and took them to .040 and it helped alot.
I think it got to where it was actually getting too much fuel.
I would check injectors/connectors. You might have one sticking open.

A very cheap cleaning meathod is this.
An old injector clip with long leads.
A small basin for the cleaning fluid. Prefferable a vibrating jewelry cleaner type thing.
A nine volt battery.
put cleaner in vibrating basin.
Put injector clip on injector and then the injector into the basin.
Put the leads of the injector clip onto the nine volt battery.
Turn on basin.
Walk away.
Come back in 30-45 minutes later.
Remove battery, injector. Replace recently cleaned injector on fuel rail.
OR you can wire in an old fuel pump and hoses and force the cleaning fluid through the injector for 10-20 minures.
In all should cost around 30 for used parts, or jewelry cleaner.

 

Wouldn't fuel problems show up on the plugs though....the colour or deposits?? The plugs all seem to be consistent in colour.

What is the pupose of the 9 volt battery??

 

the low voltage keeps the injector open.
I just put that as a possible culprit.
And running rich will not leave immediate signs on the plug, especially when it only happens at high speed. Otherwise the system works fine. So whatever evidence was there is "burned" off.
If all the injectors operated like that, all the plugs would foul. However, if only one or two injectors do that, the other 4 cylinders keep the engine running. And the other plugs on the bad injector keep firing.

 

so as far as an "on the car" injector test all you can do is test the resistance of the injectors and the harness (to see if the injector is getting a signal, right? And neither of these actually tells you really much about how it is squiting fuel, am I correct? .........or does a plugged or stuck open injector have a wacky resistance?

 

A partially open one will be "off" from the others. As when it is open, the field it creates will be different.

 

How important a test is resistance testing of injectors? and what is the spec? I noticed Haynes says 11 to 14 ohm but the 4 I tested so far are all 16 dead on. I am thinking Haynes is yet again incorrect as it would be quite the coincidence otherwise....

 

I haven't done anything yet about this particular problem basically because I can't get it to be a problem all of the time. I think the car it acting up only when it is really hot.

Does a catalyic converter "clog up" more when it gets hot?

I'll keep a problem with the injectors in mind. They scare me a little because I've never before had to deal with fuel injectors and don't know what I'm doing.

I know I'm going to change the oxygen sensor. What exactly does the oxygen sensor do? Is the air-fuel mixture adjusted according to this sensor? If you get the pipe hot and have the special socket, is it easy to change?

 

Yes, the O2 sensor reading affects the a/f mixture. Spray the sensor many times (even for days before you remove it) with a good penetrating lubricant. Get the exhaust hot. Don't use that special socket to take the sensor off, just use it to put the new one on. Get a wrench and a long pipe to put on the end of the wrench and give it a good turn. If it was installed with anti-cease lubricant, it may be easier to remove (unless it's been in there for 15+ years).

 

With things like that. In the electrical fields, standards are great, but it is more about the reletivity.
If they are all close to the same, it's all good.
If 4 are 16, 1 is 20, 2 are 15 you can spot the problem child.