Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Perhaps it is the tps gasket. By the way psi is not a torque spec for tightening nuts, blots or screws, most likely the torque spec was 12 inch pounds.
Sorry about that I was napping, been up since 7 this morning. Is is a model 220? I don't even see a gasket.
Do a cylinder balance test and see which cylinder it is and do it a few times to see if it always comes back the same one or ones or if it moves around.
First of all you will need a 12-volt test light and about 8-12 inches of neoprene vacuum hose. The vacuum hose will conduct electricity cause it is carbon based, use an ohmmeter if you are not sure and see if the vacuum hose you have will conduct.Now, cut off the same # XXXXX cylinders you have in small equal lengths of the vacuum hose. 2-3 inches will do fine. The small diameter kind like to carburetors, etc will work as long as they fit over the distributor cap tower connection.Now, mark all your spark plug wires at the cap or coil pack and remove them all. Put those short pieces of vacuum hose on the distributor cap or coil pack connections and shove the other end of the vacuum hose into the spark plug wire boot until it makes a good connection.Now connect your 12-volt test ground clip to a ground and start the vehicle. With the engine running touch the 12-volt test light to each of the vacuum hose 1 at a time and listen for the cylinder to short out and die and drop in r.p.m. They should all be about equal. If 1 or a few don’t drop or do anything than you have your dead cylinder there.
When exactly is it misfiring? You are probably going to have to re-create the misfire and catch it while doing the cylinder balance test to first determine where or which cylinder or cylinders it is coming from then go from there. With all these parts you replaced though it is going to be difficult to suspect anything unless you can make it misfire and catch it in the act.
If it is misfiring at a certain rpm, without having to rev it up too high, fold up a piece of paper or matchpack and place it under the idle screw to keep it at a certain idle while you do a cylinder balance test.
Do you see this? Do you have that paper clip icon?
THIS OPENS FOR ME IN WINDOWS
If there is a misfire then doing a cylinder balance test will at least tell you which cylinder it is so then we can start testing things.
If you suspected the spark plugs after doing a balnce test you could swap the plugs and see if the misfire moves.
I have already did the cylinder balnce test as you instructed. The test revealed all abouy equal meaning the all dropped in RPM some. If you think the plugs could be the reason even though all have a clean burn I will buy some new ones maybe autolite or AC Delco Rapid Fire? Your opinion please as I am heading out the door to work in about 30 min. I do appreciate your help in trying to resovle this. One other thing do you think I should replace the O2 sensor? It has a nice burn to it( brown). Is there a way I can test with my DVOM?
What does the label under the hood say the timing should be and why do you say you purposely have it set to 3 degrees? Are you getting a good exhaust flow? No clogged converters, crushed muffler, etc?
If you have a vacuum gauge, try this. Remove everything and plug all the holes in the valve covers, then remove the dipstick and place the vacuum gauge on the dipstick tube. It should show pressure, if it shows vacuum you have an internal vacuum leak.
If there is only one and that looks good no reason to suspect it isn't doing it's job not allowing too rich or too lean conditions from fouling it or burning it up.
I have to ask if you reved it up and kept it constant there at the rpm you said it was missing and check for the misfire then? Although you could guess by looking at the plugs or use both to confirm both.
Before finding the problem, first you have to recreate it first so you can test. If not the problem may be hidden. If it's truly intermittent even at a specific rpm, then it may be wiring, so wiggle tests may help to recreate it.
Since of so many fuel injectors a faulty injector would also cause a miss on 1 or more cylinders and could be intermittent due to wiring because they are electric driven by grounds through the ecm/pcm.
I heard of anytime you have an engine performance problem, hook up everything you got, but an oscilloscope but a cylinder balance test was all that was good for. Hook up a tach, timing light, fuel pressure gauge, vacuum gauge, code reader or since OBDI that key chain jumper, go around and inspect the exhaust and take it for a ride or not. Keep an eye on everything looking for a fault while reving up and down, wiggling wires, spraying starting fluid around checking for leaks, covering the air horn making it stall, making it run rich.
By now with the misfiring the plug or plugs taht have been misfiring are probably fouled by now but maybe not if still intermittent. Nonetheless, they should be inspected to look for rich or lean mixtures, oil or carbon, etc and might as well replace them.
If you ever find the misfire, swap a spark plug wire and check again. If still misses there and didn't move than either disconnect the fuel injector wires and do a balance test like that to see if it makes a change. If after that and nothing measure camshaft lobe lift on both valves.
Dropping 40 to 80 RPM routinely is probably 1 cylinder misfiring and the 300 rpm is most likely 2.
If you knew which ones you could move the plugs and wires around and follow the miss or if it stays right there it's not a plug or wire.
A distributor can looked timed but, if you were to look down at the pickup coil and the tooth on the shaft they may be off when the rotor is facing #1 on the tower. What this causes is the distributor to fire in between towers. I didn't say it was I just said it could have been.
The manual I have says refer to the underhood label for idle speed but 550 rpm seems a bit low, as a matter of fact the 1988 and 89 models they do list the idle or and they have it listed at 700 rpm.
Ok, a pressure during that test is a good thing, that passes.
If you have a vacuum gauge see how much intake manifold vacuum you have at idle. It should be at least 17 inches and 19 inches would be great.
Look at the fuel injectors while it's idling and look for any fuel dripping, there should not be any drips.
If it does have a miss at idle you may at least be able to tell which bank it is if it is a dualk exhaust by going around to each tailpipe and put the palm of your hand about 6 inches away from the exhaust gas and feel and look and listen for any spitting and sputtering. Plus then smell your hand and smell if you smell gas or if the exhaust burns your eyes, that is too lean, like gas too rich.
I don't know if I gave you one yet or not, but for the testing procedure for the idle air control valve, click here.
Also, if you have a scan tool you can check if the IAC circuits are clooged or if there may be a vacuum leak.