Cylinder missing

[Poriomania]

My engine died ealier this week and that was traced to a break in the wiring harness. It still misses sometimes though. I thought I would work with it some this weekend to see if I could get it straightened out. I'll check the distributor and the wiring to the EGR and the loom that goes behind the glove box. I'm going on the assumption that it's likely electrical. Is there anything else I should check?

 

[semlin]

vacuum leak in a vacuum line or the big air intake bellows?

there is almost no wiring to the egr and what there is is unlikely to cause a miss. by checking wiring to the EGR do you mean the engine harness wiring where it runs beside the EGR? is that where you had the problem last week? that's where it usually goes and where i'd start.

 

[cruiserdan]

OBDII should tell you if it is a single cylinder or a random mis-fire. If it is a single cylinder I would look at the injector wiring or the injector pertaining to that cylinder.

 

[cruiserdan]

Usually it's easy to identify if a single cylinder is missing. A quick visual examination will determine which one is gone. Finding it can be another matter especialy if it went missing while the vehicle was in motion. They can end up alomst anyplace.

 

[Texus]

Ha!

Ha! (as per Dan's remark)

 

[tucker74]

Check your plug wires - mine was missing cyl #5 and I tracked it down to a bad set of Bosch wires from the PO

Tucker

 

[John E Davies]

A quick and effective method to find the bad cylinder is to use an infrared temp gun. With the exhaust shields off and the engine idling, the misfiring cylinder will show up as noticably colder (up to a couple of hundred, depending on the severity of the miss.)

Good luck on this one. Don't discount coincidence - you may just have a bad plug lead.

John Davies
Spokane WA

 

[semlin]

wouldn't it be a lot easier to remove the plugs in order and see which one makes no difference?

 

[Poriomania]

Can you pull the throttle body off without draining any of the radiator fluid? Seems like it's above the cold level of fluid.

 

[semlin]

you will lose a thimble full if you are careful and do it cold.

 

[Poriomania]

I took the truck to a parts store that lets you borrow their OBDII reader and it came up that cyl 3 is misfiring. I check the injector resistance and it seemed be within spec. I checked the plug wire and it is supposed to be 25K ohm and is reading at 12.8. The manual notes that if the wire reads at a higher resistance it should be replaced. I'm not schooled in electronics, but mine is reading lower right? If it is reading at lower resistance is this still likely my problem?

 

[landtank]

if the resistance is lower than the wire is good. I just had a miss fire on #6, the connector at the injector fell off.

 

[Poriomania]

So, to be clear, when mine is reading at 12.8 when spec is 25 it is good?

 

[landtank]

yes it is fine, no need to replace.

 

[Poriomania]

I'm at a loss as to what to check next. The injector checked out and so did the plug wire. The problem doesn't occur at idle, only under acceleration and when trying to maintain speed. This doesn't seem electrical. The next items in the manual diagnostics are:

fuel line pressure
EGR
compression pressure
Valve clearance
valve timing
MAF meter
Engine coolant temp sensor

Would any of these affect a single cylinder in the above conditions?

 

[semlin]

have a look inside your dizzy cap and hope like heck there is a problem with the contact at #3. also, go back to where they repaired the harness. maybe they missed a bad wire to the injector.

otherwise, it is time to consider the h/g although #3 is not a typical place for it to let go. try the bubble test and compare the #3 spark plug to the others nearby. If you see more or less carbon on #3 then h/g is likely.

 

[CJF]

This doesn't seem electrical.

Why not? What does it feel like? An intermittent, quick little "jerk" when accelerating or, as you said, maintaining speed is often electrical. Happened to me and it was indeed a bad plug wire.

How old are your plugs, wires, and dizzy cap & rotor?? Even though you've "checked" them, personally, I'd replace all that stuff unless they're pretty darn new, and definitely if they're not OEM.

Curtis

 

[Poriomania]

Why not? What does it feel like? An intermittent, quick little "jerk" when accelerating or, as you said, maintaining speed is often electrical. Happened to me and it was indeed a bad plug wire.

How old are your plugs, wires, and dizzy cap & rotor?? Even though you've "checked" them, personally, I'd replace all that stuff unless they're pretty darn new, and definitely if they're not OEM.

Curtis

I say it doesn't seem electrical because it doesn't do it at idle, and that it's not one stutter then normal. It runs so bad I can't even pull up a small hill. I noticed today on a short run it was much worse after warming up. All the spark stuff was replaced OEM a year ago January.

 

[landtank]

compare the #3 spark plug to the others nearby. If you see more or less carbon on #3 then h/g is likely.

Since he already has a confirmed miss at #3 I'd suspect the plug to look different whether or not the HG is good. I don't think seeing a difference would necessarily mean a HG failure.

I personally would do a full tune up, plugs, wires, cap and rotor. But if you want to try and save some cash you could jockey things around like the plugs and wire to see if the problem moves. If that doesn't change things then a cap replacement would be next.

 

[landtank]

I say it doesn't seem electrical because it doesn't do it at idle, and that it's not one stutter then normal. It runs so bad I can't even pull up a small hill. I noticed today on a short run it was much worse after warming up. All the spark stuff was replaced OEM a year ago January.

One thing you might also try is do a brake stand in both drive and reverse and see if the truck behaves differently. We've see it where under load the engine will torque and produce an electrical problem. Since the motor torques in opposite directions between drive and reverse it might not show up in reverse which would help eliminate some of the searching.