99Cavalier

I have a 1999 Cavalier with 2.2L and automatic. It has 121,000 (98% highway) miles. It has been very reliable and was getting about 32 miles per gallon. About a month and a half ago, besides getting brakes, they (dealer) cleaned the fuel injectors, intake, put a new fuel filter on.

Car ran great for about 2 weeks (I don't think this service has anything to do with issue, just letting you know last service). This seemed like a sudden event (fine one day, started next morning). When you start the car, it starts immediately. After a few seconds the idle gets very rough (like an older V* lope with a race cam). The engine will not stall or quit, but you can watch it shake with the hood open. After the car is warm its not as noticeable, but you feel the miss sitting a traffic lights. There is a point between the engine being cold and up to temp where you barely feel a miss.

Plugs were replaced about 20,000 miles ago, wires 60,000 miles ago. Only other parts were serpintine belt at 70,000 and an alternator a year ago.

All you have to do is barely step on the accelerator and it gets smooth. There is no jerking or hesitation when starting off and driving (even at 5 mph or more) is smooth as ever. The engine check light is NOT coming on. My mileage though is now about 28-29 mpg.

I took it back to the dealer about a week after it started to make sure one of the injectors wasn't plugged and they all checked out OK. They did a compression test and 3 were 182'ish and the 4th was 153. They thought maybe that cylinder was causing the miss (I've always heard around 140 is the low end of acceptable?). I don't agree; if it was a compression issue it wouldn't start immediately and run OK for a couple seconds,plus I don't see where it would be fine one day and do this the next. I haven't but plan to have another compression check done to see if it agrees). The other possibilyty they mentioned was a vacuum leak (but at $85 an hour to keep checking I decided not to as they had put 2 hours in it already with no answers). I decided to pursue that on my own.

I've since discovered that the 99 Cavalier (at least mine) does not have a PCV valve (its a built in air/oil seperator in the valve cover which is not plugged) and does not have an EGR valve. The local parts store had a listing for a 1999 but where they and a Haynes manual says it is there is nothing on mine. I checked with our Chevy dealer who did the work and they confirmed mine does not (surprising to me).

The problem is no worse or better, the car hasn't stalled, but I feel there has to be something that has caused the sudden issue. Can anyone offer some tips to check (since it has no PCV and EGR which often cause this type of issue I don't know where to look next).

beckeruti

have a oscilloscope hooked up to it when it is cold and start it and see if it is a spark issue

when you see the engine shaking move the plug wires around and see if it goes away
or if u get a shock
if it goes away or u get zapped
its in the spark

oh by the way getting zapped doesnt hurt just scares you

good luck

99Cavalier

If one of the cases is true (I get zapped or mis-fire goes away) is that saying its the plug wires (and to replace them)?

beckeruti

yes or maybe some over night moisture is getting into the boots or some corrosion is in there somewhere
causin a loose connection

and if you find one to be a suspect you could replace it

last weeek i cleaned my motor near dark
next morning i had the same symptom engine shaking goes away when revved
i turned it off moved wires around made sure the connections were snug and it hasnt done it since

99Cavalier

Well, I played with the plug wires; and didn't get zapped nor did it make any difference in idle. Anything else that can affect idle only mixture etc?? Its weird that it runs great just off idle.

99Cavalier

Here is an update. I still haven't found the cause (I also found a lot of similar posts about Cavaliers with similar symptoms and found no answers to those either). I bought an OBD II reader ($39.00 at Harbor Freight). It had two codes.
P0200 (open injector)
P0304 (Cylinder 4 misfire)
P0304 Pd (Pending, Cylinder 4 misfire)

Does anyone know how it determines a misfire in a particular cylinder?

I inspected the #4 wire and it has several cracks or slits in the rubber insulation down to the inner shielding. I put some silicone on them and electrical tape; it still is missing but does not seem as bad. I plan to put new wires on this weekend.

The #4 cylinder is the one the dealer said had 153 PSI compression test reading. From what I can find 140 and up is acceptable (can anyone validate this??) Perhaps with the wire and lower compression its more sensitive?

Here is some suggestions from another site:
Causes
A code P0304 may mean that one or more of the following has happened:
[ul][*]Faulty spark plug or wire[*]Faulty coil (pack)[*]Faulty oxygen sensor(s)[*]Faulty fuel injector[*]Burned exhaust valve[*]Faulty catalytic converter(s)[*]Running out of fuel[*]Poor compression[*]Defective computer [/ul]

golfer

You did the proper first step and pulled the codes.

Have checked the reason for P0200 ( open injector ) ??
If the fuel injector is not working on that cylinder you will have a misfire because of no fuel.

99Cavalier

The P0200 might have been when I had the dealer look at it initially (which was a few weeks after they had cleaned the injectors and intake). They swapped injectors and plugs between a couple cylinders to see if the misfire went with it. I would hope they would be able to figure out then whether an injector was working or not?

They came to the conclusion the lower compression was the issue and recommened a rebuilt engine (at $3,500, which I passed on). I can't see compression becoming a factor seemingly overnight.

If the new wires don't help I plan to just drive it till next year (it hasn't gotten any worse, still hasn't stalled or the like) and then decide on what to do.

beckeruti

if u can swap number 4 injector with another and see if the misfire follows
now that u have a scanner
can u clear codes with that scanner
good luck

99Cavalier

Dealer did that, mis-fire stayed with #4. After siliconing/taping the crack in #4 plug wire, the mis is there but seems less. I still plan to replace the wires this weekend.

The original ones were replaced on a recall due to some issue with internal resistance about 60K miles ago. The symptoms were similar in that the when idling the engine would occasional mis and shake (though this time its steady and worse).

I did some further checking on specs, the manual (Haynes) states that the lowest cylinder compression should be within 75% of the upper and be above 140 PSI. My reading on cylinder #4 was 153 and the others were about 182. That puts it at 84% and within specs for lower reading.

I will clear the codes when I put the new wires on and we will see where we go.