My stock '88 Vette automatic has almost 160,000 miles. I know it's time for a rebuild but I hate to retire this engine when it is running so well - except for the lack of power. It runs very smooth, idles smooth, starts consistently (2 to 3 seconds of cranking), gets 26 MPG on the highway and uses about 1 quart of oil between 5,000 mile oil changes. There's a slight blue exhaust haze at startup. It (barely) passed the California emissions test about a year ago.
Here's my question: If the engine seems to run so well, why has it lost so much power in the last 2 or 3 months? I would estimate that power has dropped about 20%. When I stomp on the gas at 45 MPH, it downshifts into 2nd and accellerates steadily but weakly. As the RPMs rise, the accelleration just goes flat. Eventually, it will gain enough speed to upshift into 3rd. There's no hesitation, popping or roughness. It just can't seem to breath. I live at 1500 foot elevation. The stock air filter is clean. The fuel filter is new. I have 3 suspicions:

1) The original catalytic converter is plugging up
2) The cam lobes are wearing down and providing less valve lift
3) Engine compression is going away

What do you think is most probable and how can I quickly and easily narrow it down? It may be a combination of all the above.

Thanks in advance for your feedback.
Greg Sullivan

 

No. 1 nd No. 3 are good possibilities...but the cam lobes are fine, as roller cams hardly wear the lobes down.

 

You have 3 cats on a 88 Vette.
Anyone of them could be clogged at 160K miles.

Good luck

Vic

 

Greg,
Check the spark plugs for deposits and fouling and have a leak down test performed on the cylinders. Chances are you will find a 20 to 30 % loss which is the reason for the oil smoke. If its over 20 % its time to do the engine. My 89 had 168K on it when it finally fouled out #6. All the cylinders had more than 20% leak down. Besides the engine condition, with that much mileage you could still have a cat. problem. There is a way to check the temperatures in front of and behind each cat to tell if it is stopped up or not. Some of the exhaust shops can do this and have the proper temp. info.

 

check those ignition components, and those cats are prolly clogged up

 

If you still have the original front y pipe with the precats i would suspect that they are going bad! :cheers:

 

Thanks for all the great feedback. The spark plug wires are new (they're called "Firewires" - over $120 for the set). The distributor was completely rebuilt. GM didn't offer a new one. I don't think I could get 26 MPG on the highway if there were any serious problems with ignition. I have new Bosch Quad Platinum spark plugs. The lack of power probably coming down to compression or the catalytic converters are clogging up. Everything behind the main catalytic converter was replaced. The main cat and pre-cats are all original. Can they fail in a way that restricts exhaust or do they just chemically fail? I have an infra-red thermometer that I could use to measure catalytic converter performance. But that wouldn't tell me if it is plugged...would it?

Thanks,
Greg Sullivan

 

if your cats are clogged then it usually means the stuff in there has broken up into pieces, not a chemical failure. Yeah you should be able to tell by a thermometer whether or not theyre too hot (restrictive). Sometimes theyll even glow. Better to replace the whole front Y and Main cat, or you could go the Headers route and eliminate the precats.

 

When I put a new distributor / cap / rotor and ignition coil on my 100+k car it really picked up a lot on the low end. In fact I can now do burnouts! :jester: I still have the original plug wires at 111k. :) ~Juliet

 

Juliet-- I have 107K. Did you get an entire new distributor or just cap and rotor? Did you install it yourself? How hard is it to put it in the right place?

 

No, I didn't put in a new distributor. Sorry, I haven't had to do the align thing yet so I can't help you there. Sorry. I don't think mine needs one yet anyways. I got cap, Hi Perf coil (shhh, don't tell NCRS!) rotor, ignition module, and I forget what else. Basically the whole shebang. I vacuumed out the old bits of rotor & metal debris from when my old (original!) one went suicidal on me. Fortunately there's a screen there to catch debris before it falls down into the engine or I'd be doing a rebuild by now. :eek: If yours hasn't been changed don't risk stranding yourself. My C4 had to be flat bedded home that night. One of the metal posts where the plugs attach fatigued (corroded?) on the inside and the metal inner part lining the cap fell down. Of course the spinning rotor chewed it up and mangled itself and the whole thing basically self desctructed within a few minutes once I heard that 'funny sound.' I had stopped and opened the hood trying to tell where it was coming from when he died. :(

 

Another way to tell if your cats are clogged is to have your dealer perform an exhaust backpressure test.

 

Cat

 

Greg
In a round about way you already given your self the answer to your own problem. All new stuff and you still don't pass emissions. That almost proves that they are bad. I put a new cat on my 85 clocking 155K on the meter and the emissions guy couldnt believe the engine was origional. The Cat cleaned up all of the emissions. I have a rod knock and bad valve guides and I still pass with flying colors. If you live in an area that checks emissionsand have to pass the emissions, treat your vette to the best set of cats that there is and be happy. Replace the cats and I think your problenm will be solved (pretty much :rolleyes: ) Theres nothing that strokes the ego like a rebuilt engine!!!! :D The wallet wont be happy but the seat of your pants will!

Bill C

 

I would start by replacing the O2 sensor. These usually require replacement in the 90,000-100,000 mile range so with 160,000 miles this is not money thrown away. If this does not solve the problem entirely then it probably is the cat(s). In fact, if the O2 sensor was failing and sending the wrong info to the engine computer (ECM), the ECM may have been incorrectly enrichening the mixture, causing the poor smog test performance. The downside if this happened, the cat(s) may have been permanently fouled by the excess (and unburnt) fuel. If you have to replace the cat(s), go aftermarket! The technology has changed, better perfomance all around and cheaper!

 

Greg....

...I noticed your L98 ran/runs just about what mine did stock also; this may provide some help if anything. My first time to the track ever I ran a 14.6. I then learned my main cat was clogged up majorly. I replaced it and ran 13.892.

Seems like you know what you are doing so carry on. I would check...

1. Plugs
2. Wires
3. Cap
4. Rotor
5. Timing
6. TPS
7. Main Cat
8. Pre-Cats