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Recently my engine started running very rough like a cylinder was missing. I tested the spark plugs, wires and distributor and found that they were all working properly. I even swapped them out with known good equipment just to verify it and got the same results. The air going to the engine is fine. There are no restrictions or issues with airflow. Lastly, I have verified that each of the fuel injectors are getting the correct voltage sent to them.
What I haven't done yet is checked to see what the spray pattern is for the injectors or the condition of the valves. I'm pretty sure that the injectors are working well since the issue happened all of a sudden while driving one day. This leaves the valves as the possible failure point. I know that the best way to check them is to pull the head off and inspect them, but I'm wondering if there's a way to do a lesser inspection that may shed some light on the problem without pulling the head off. Is it possible to, at least in a basic sense, determine if I have a bad valve by pulling off the cover to the cams and, possibly, removing the cams to check at least part of the valve's operation? If I were to pull off the cams I believe that the valves should all be closed, so if I was to pressurize the cylinders via the spark plug hole, then I should be able to check to see if a valve was leaking, right? Has anybody done a check like this before? Pulling the head off is pretty expensive to do if it's not part of the problem, but if it comes down to it then I'm totally comfortable doing it. I just don't want to do any more work than necessary.
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It looks like cylinder #4 is having compression problems. All of the other cylinders have adequate compression, but a simple compression test has found the base issue. I need to perform a leakdown test to find out what part is failing, but I can't seem to justify paying $150 for a tool that I'll probably use only this one time. If anybody in the Seattle area happens to have one that I could borrow for an afternoon, I'd by you lunch if you would let me use it. Really all I need is a hose that'll attach to an air compressor and to the spark plug hole so that I can put enough pressure in the cylinder to hear where the leak is.
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posted by
someone claiming to be fixit2002
on
Fri Jul 6 07:50 CST 2012 [ RELATED]
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Before you do all this just try a compression check and add some injector cleaner to the gas. Check the intake bellows for cracks. Remove and check all the vacuum lines and associated PC lines. Is it bad gas? I believe your car has a fault code reader on board. Are there any diagnostics codes? Remove the throttle body and clean it thoroughly along with the flame trap tubing connection ports.
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Wouldn't a leakdown test pinpoint which valve (if any) are sticky? If you have the equipment, this might be the next step.
Fuel injector getting the right voltage doesn't mean it is spraying properly. Which cylinder is struggling? The computer should tell you which cylinder is at fault. Was there oil in the nooks/crannies near the filler cap/blow-off hose?
There is no reason to pull the head for diagnosis.
How did you verify airflow is not impeded?
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If you're not driving it "like its stolen," are you really driving?
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True, the voltage check on fuel injectors will not determine spray pattern, but I've not heard of any injectors all of a sudden failing like this before, so that's why I'm reasonably confident that it's not them. I should check them anyway just to be sure if other checks turn out ok.
The computer is pre-OBD-II, so it's not as useful, but never the less I checked it anyway (forgot to mention that detail in my original post). There are no errors related to the engine on it. Just a couple for ABS sensors not getting a reading once in a while.
What is a leakdown test? I was going to perform a compression test which would tell me if there is a leak in the cylinder, but that's assuming that there's not a leak someplace else like the rings, so I still may not know if it's a valve, right?
Another guy posted here suggested checking the hoses and throttlebody, but it doesn't feel like it's a problem with all of the cylinders. Just one, maybe two of them.
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I agree. But because he is not getting codes for misfires, it don't suspect it is a valve problem. He didn't mention Tbelt replacement, but if it is off a tooth for a long period of time with the 1994, it will also 'mess up'.
I wonder what codes he gets on A-6?
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My name is Klaus and I am a V♂lv♂holic
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Yeah, he left the codes part out of the first post. Then I figured knowledge on a leak down test wouldn't be a bad thing, and running it won't hurt anything either.
I thought A-6 codes still set off the light, but perhaps the bulb is burned out? He said he has codes in A-3, so perhaps he checked them all and there was nothing in A-6.
I had an issue with my wire to #3 being cracked and sparking on the block occasionally. Several weeks went by where occasionally it'd run with some hesitation at the unusual times (55mph, as I'm shifting into second while accelerating), and one rainy day i found it, watching the spark go. Not once did it set a code. I'm not real sure how it calculates misfires, but I think valve issues would show up. Air leaks tend to show up as fuel trim codes, but they can take a while to do so.
Would being off a tooth get all the cylinders or just a few?
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If you're not driving it "like its stolen," are you really driving?
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It could even be something simple like a heavily carboned combustion chamber.
The misfire comes from the knock sensor, strangely enough. Don't ask me how that works, but it sounded good at the time.
Remember, some codes are stored pending reoccurance. Misfires, except multiple, are like that, so an occasional misfire will not turn the CEL on.
A 'sticky' valve, which is not really sticky - just doesn't close completely due to carbon on the valve seat - can sometimes be cured by gently blowing the carbon out. Some of these owners never go over 2500 rpm for weeks at a time, and use regular gasoline.
Oh well, I just sit here waiting for a post that has lots of words and real good descriptions of the problem.
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My name is Klaus and I am a V♂lv♂holic
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There are no A-6 error codes that were reported. I'm going to start with a compression test to see if the compression is at least getting up to a normal level and then may do a leakdown test if I see anything that looks too far out of spec. The car isn't really drivable right now since it has a massive loss of power, but it will turn over and *usually* stay running at idle with the occasional goosing of the gas when it starts to bog down in RPM. I recently put some Marvel Mystery Oil in with a new oil change to see if that may clean things up a bit, but I'm thinking about putting some sea foam in the intake system to see if that cleans things up a bit.
So, recap of where I'm at:
- No error codes related to the engine
- New spark plugs, cap, rotor, and wires (my old wires were actually looking really bad and I've been wanting to replace them anyway)
- Oil change with filter using 15W-30 oil and Marvel Mystery Oil
- Timing belt is old, but is still in good condition. It's very unlikely that it has slipped a tooth but I can certainly check that.
- When the engine starts, it feels like one cylinder is missing very badly. The interesting thing that I found on a test run, though, was that it ran perfectly for a few miles before it began missing again. At this point it misses even cold.
- Spark has been fully tested, so I'm confident that the electrical system is in good shape now
What I need to do:
- Check to see if I at least have the correct voltage for the fuel injectors (yes, I know that this isn't going to tell me if the spray pattern is good, but it's the first step)
- Check the timing of the engine
- Perform a compression test on each cylinder
- Based on the results, I may also perform a leakdown test
- Run sea foam through the intake system to clean out any buildup that may be present
- Re-do the compression or leakdown test to see if things improve
Anybody see anything that I've missed that they think I should check at this point?
Thank you all for your help so far. I really appreciate it!
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I've been busy recently and haven't been able to work on my car much, but this last weekend I was able to perform a compression test on the cylinders and found that #4 is very low on compression. I'm going to perform a leakdown test on it when I can get the tool. Although I may need to tear the engine apart in the end, if it's the intake or exhaust port that is leaking then I may put through some seafoam first just to see if that clears things up, but if it's not the valves then it's probably the rings. If the rings are the problem, then I'm going to have to make a big decision about what I want to do with this car since that's a lot more work and $$$ to fix.
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Have you checked fuel pressure to verify it is correct?
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If you're not driving it "like its stolen," are you really driving?
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Not yet, but last summer I replaced the fuel pump and filter, so hopefully that's not an issue. I do have a pressure gauge for testing this, though, so that's an easy one to check. When my fuel pressure was low I noticed that it would just cut out as opposed to give me a missing feeling.
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The pressure regulator could be causing the pressure to vary enough causing this.
How was it doing at high (over 3k) rpms?
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If you're not driving it "like its stolen," are you really driving?
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It still runs a little rough at higher RPMs, but smooths out a little. You can feel the occasional miss at times. Below 3K it's really rough, and will possibly die when idling.
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Do NOT remove the cam cover! It is RTV'd in place and a bear to put back on. The valves are not all closed, it all depends on where the cylinder and cam are in alignment.
Do a compression test with a warm engine only. If one cylinder is down, then add a tablespoon of oil to that cylinder, and, if the compression goes back up it is not the valves.
Because you do not have codes that point to a misfire, pull all 5 spark plugs and look for deposits. Too much fuel would indicate that you are running rich because of a vacuum leak - check all the lines that connect to the intake manifold as well as the plastic vacuum tree itself. The large hose from the idle air control motor to the top of the vacuum tree can get loose or crack.
Rather that pull the injectors and trying to see if there is a good spray pattern, get 2 bottles of Techron cleaner and pour them into your tank full of gas and go for an hours drive.
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My name is Klaus and I am a V♂lv♂holic
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