Very rough idle and chugging under load

ouroboros314 · #1 03-13-2009, 01:23 PM

1991 Accord Lx

I was driving on the highway the other day and was around 70 mph when the car started shaking. The shake lasted for about 10 seconds so I didn't think much of it until I pulled in for some gas. When the car got into the lower 20 mph the shake returned and was very prominent at idle. I got gas and managed to get the car home.

I have a feeling this rough idle and chugging is due to a dirty/clogged fuel injector. I added some Gumout fuel injector cleaner about 4 days ago during routine oil change and believe the cleaner freeded up some build up in the system which made its way to the injectors and is now clogging them. I checked the spark plugs and did notice a large carbon buildup on plug #2 and suspect this is due to the clog in injector #2.

Would like to fix this problem as cheaply as possible since I am a poor college student.

Thanks for the help

jeffcoslacker · #2 03-13-2009, 09:06 PM

Dry carbon buildup is soot from unburned fuel. If it's wet, and smells like fuel, you have an ignition miss or that cylinder is running very rich, possibly due to an injector sticking open and leaking when it should be closed.

First question is, did you change the plug(s)?

It sounds like it just fouled a plug, from the way it acted. Don't get ahead of yourself.

There is rarely any crud in the system other than at the injector tip. Because the orifices are so small, they can be clogged by minute particles, and sometimes buildup can prevent the injector pintle from seating completely, making the injector leak when it should be closed...but cleaning rarely causes restrictions. Plus that stuff is just not that aggressive.

You should be able to hear the injectors operating if you put a wooden rod to them and your ear...they make a sharp clicking as they operate. Make sure you don't have a dead one...check it's wiring harness if you do.

Also make sure you don't have a carbon track with "halo" on the underside of the distributor cap, or a cracked cap.

ouroboros314 · #3 03-15-2009, 03:46 PM

Just replaced the plugs. Seemed to help a little bit but the idle is still rough. I am going to check the injectors with a wooden rod as suggested, see if I can locate the culprite.

I am confused about the "halo" and carbon track near the distributor cap warning. Can you go into more detail what I should be looking for.

Thanks

jeffcoslacker · #4 03-15-2009, 06:19 PM

When you take the cap off and look inside, a crack will usually be filled with carbon, which conducts just like a terminal, stealing spark from the closest plug wire tower. The high voltage running along the surface of the plastic leaves a distinctive effect that highlights the crack, which is sometimes very hard to see itself. Usually the plastic is discolored slightly and looks kind of "iridescent" around the area where it's cracked. That is called a halo.

Check the plug wires too, if you bend one into a tight loop around your finger and can see cracks in the outer sleeve, they are shot.

Pull that new plug out of that cylinder and see if it's wet or sooted already...

ProMan · #5 03-16-2009, 10:08 AM

Make sure you got spark for all 4 cylinders (assume it's a 4-cylinder engine). Engine shaking at idle could be a firing problem and maybe one cylinder doesn't fire up.

One easy way to test is to pull the plug wire one by one. If that cylinder is fine, when pulling the wire away, the engine will jerk and shake worse. If the engine runs the same as you pull away the wire, then that cylinder is not working. Then you can start from there.

mpumas · #6 03-16-2009, 11:30 AM

I recommend removing the wire at the distributor end rather then the spark plug end. Sometimes removing at the spark plug end while the engine is running can cause a electrical shock .

jeffcoslacker · #7 03-16-2009, 08:34 PM

Quote:

Originally Posted by mpumas

I recommend removing the wire at the distributor end rather then the spark plug end. Sometimes removing at the spark plug end while the engine is running can cause a electrical shock .

I don't pull them while it's running...just pull one and start, see if the idle rpm drops from previous reading.. About 150-200 rpm drop when a working cylinder is disabled is typical.

I think he pretty much pinned it down when #2 came out fouled though..

It's not a bad idea to put a spare plug in the wire you pull and ground it during testing.., not allowing a wire to fire to ground through a plug can cause the spark to jump inside the distributor, possibly zorching components inside...

ouroboros314 · #8 03-22-2009, 04:44 PM

Ok, finally got some time today to screw around with the car to figure out this problem. I first began by testing each fuel injector by disconnecting the harness to each injector one at a time. The only injector which did NOT drop rpms when disconnected was #2. I then did the same thing with the spark plug wire suggestion. Again, cylinder #2 didn't have an rpm drop. To check spark I just leave the plug in the wire and turn on the engine?

ouroboros314 · #9 03-22-2009, 04:45 PM

Oh I also pulled plug #2 and she is wet and dark

ouroboros314 · #10 03-24-2009, 01:06 AM

bump

somick · #11 03-25-2009, 11:33 AM

Quote:

Originally Posted by ouroboros314

Oh I also pulled plug #2 and she is wet and dark

Does it get spark?

ouroboros314 · #12 03-25-2009, 05:44 PM

I don't know, can I just check spark by leaving the plug in the plug wire and starting the car?

somick · #13 03-26-2009, 01:36 PM

Quote:

Originally Posted by ouroboros314

I don't know, can I just check spark by leaving the plug in the plug wire and starting the car?

Yes. Make sure you GROUND THIS PLUG. Hold it tight against any metal part of the engine. Have somebody to crank the car and watch for the spark between electrodes.

Sam

ouroboros314 · #14 04-04-2009, 02:42 PM

Ok, finally got around to testing for spark. The spark plug does fire. By process of elimination I can only assume the fuel injector is messed up. I found a set on ebay for cheap but the question is how hard are they to replace. Doesn't seem to be more than disconnecting the wiring harnesses and the fuel line. After that, remove the old and put in the new. Never done this before though so it might be more than I think. Suggestions?

somick · #15 04-04-2009, 05:52 PM

Quote:

Originally Posted by ouroboros314

Ok, finally got around to testing for spark. The spark plug does fire. By process of elimination I can only assume the fuel injector is messed up. I found a set on ebay for cheap but the question is how hard are they to replace. Doesn't seem to be more than disconnecting the wiring harnesses and the fuel line. After that, remove the old and put in the new. Never done this before though so it might be more than I think. Suggestions?

You need to find out how healthy the spark is but since I am colorblind I am not big help here. Visit www.tegger.com for testing procedures.

In order to replace fuel injectors as far as I understand you need to relief the fuel pressure. There should be a relief valve somewhere on the fuel rail.

Good luck,
Sam

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