Truck was running fine, but suddenly developed a servere misfire and power loss. Happened at a stop sign on a residential street. Was able to limp the couple of miles home, but couldn't get above 25-30 mph.

No warning lights, not overheating, oil & coolant are good. (Haven't done anything more because we're having a snowstorm.)

My first guess is that it somehow jumped timing, though I replaced the chain & tensioner 3-4 years ago, and only drive it around 5-8K miles a year. Does this seem reasonable, or are there other possible causes I'm missing and should look at before tearing into things?

 

Got any videos of it running?

 

I've had this experience on other vehicles with a coil failure

 

No, I haven't even tried to start it, due to the aforementioned snowstorm. (Don't have a garage to work in :-() Supposed to clear up a bit tomorrow.

How could I test that, other than just buying a new coil and seeing if the problem goes away? Google gives some info about testing the winding resistance, but wouldn't the shorts or broken wires that would be found this way mean the coil wouldn't work at all?

 

Unsure if a ohmmeter test of the coil would pick up on this. What I'd do:
- First, look for rat-chewed wires. They are evil creatures that wreak havoc for fun.
- Second, check the timing and see that it's right
- If it's okay, then check that you have a good hot spark using either an old plug or pulling one out. Don't run the engine with a plug wire not connected to something
- Read upon the ohmmeter test of your coil and see if it passes


When I had a coil fail ('72 Chevy truck), it would idle fine, but any load on the engine would cause it to stumble.

 

Any update; how is everything going?


 

Snow finally stopped, so I got out and pulled the valve cover yesterday. It does look like it jumped the timing, unless I misunderstood the manual. At TDC, the two bright links on the chain (circled in red) should be at the top, where the (badly drawn) green arrow arrow is, no?

I've also attached an audio file of it starting and running for about 30 seconds.

 

"Jumped timing" does NOT sound reasonable. Likely problem lies with injector(s) or ignition. My $0.02

 

Do you have one of those indirect (IR) thermometers? Let it run awhile and use it to check the exhaust manifold temperature at each cylinder outlet. That'll tell you if the issue is associated with one cylinder.

 

I don't, but if it was one cylinder, I'd expect the plug to be fouled, or at least wet. Pulled them, and they're normal.

Besides, the loss of power is so great that I think it would have to be more than a single cylinder. Nor does it really sound like just one cylinder misfiring...

 

I don't think you are at TDC, for a couple reasons. First, I think the bright link(s) lining up with the mark on the gear is only when first installing, after some rotations I don't know that the link lines up again. But second thing, there is a timing mark on that distributor gear there at the very front of your engine. I don't see the timing mark, so I think you need to rotate around another 180 degrees and see if that timing mark comes to the top. And then look at your rotor under the dist cap and see that it should be pointing pretty close to #1 plug.

 

You're right. (Kicking myself for not thinking of it.) It does seem the timing is right: with the crank at the TDC mark, the cam mark is at the top and rotor at the #1 plug. So that rules out timing as the cause, I think.

 

Been sick for a while, so only got back to working on the truck today. So far: 1) Timing is good; 2) Coil tests ok as far as I can do with just a multimeter; 3) Has a strong & regular spark on all cylinders; 4) Exhaust seems to have a strong flow, like normal, so the problem probably isn't due to a blockage of some sort.

One odd thing: when I tried to start it today (after sitting for a week), it would crank but not fire. Had to give it a squirt of starting fluid, after which it took off, ran, and would restart easily. This isn't nomal for the truck: unless it's below freezing (cold start injector switch :-(), it always starts right up, even if it's been sitting for weeks. So I'm thinking it might be a fuel supply problem. However, I've no idea how to test this. The shop manual mentions using another banjo bolt fitting at the cold start injector, but I don't have anything like that, or ideas on how to rig one with what I've got. And any other connection (fuel filter, for instance) seems to require some significant disassemble to access.

So could some sort of block or failure in the fuel supply be causing this? And how to test it? Any advice or ideas would be welcome.

 

James - well one thing you can check is the cold start injector flow while cranking. If you search on here, I know some people have done this and have reported how much fuel to expect. What you do is unbolt the cold start injector from the intake, but leave the fuel line and the electrical plug connected, stick it into a jar to catch the fuel, and then crank with the engine cold, you should get a certain amount of fuel. I think you can also pull the coil wire so engine won't really try to fire up. This might be described in the FSM, I cannot remember.

 

Been able to work on the truck a bit more. Checked fuel flow at the cold start injector. Seems to be squirting out plenty of gas, though I couldn't figure out how to get a large enough container in there to actually measure the amount.

Checked the timing, and it's right on the spec 8 degrees BTDC. Also did a compression check: fairly low, around 120 PSI, but all the cylinders are the same. (It is an old engine, with maybe 350K or more on it.)

Replaced the ignition coil, but that didn't help any.

I'm completely at a loss now. Could it be a vacuum leak somewhere? I think I've checked all the hoses, and they're good, but maybe something is hiding somewhere that's not obvious?

 

I agree 100% with looking for rat-chewed wires. I had a bad plug wire that caused what you are describing. It wasn't easy to see until I pulled it and really looked it over.

 

Did look for chewed/bad wires, and vacuum lines, but didn't find anything. I don't see how that would cause the sudden problem, though. It's not like it'd been parked so critters could chew on the wires, then the problem happened when I tried to start it. (Actually had that happen with another car.) I'd driven it about 30 miles - up the mountain for cross-country skiing, then back. Ran fine until I was nearly home, stopped at an intersetion, then it suddenly started the misfire when I started moving again.

Also, if I didn't mention it before, it also idles poorly: barely runs, if it doesn't stall out.

 

Any chance your EGR is stuck open? It is supposed to only open at operating temp and under certain vacuum conditions, but perhaps it is stuck open. You could probably pull it from the intake plenum and use a temporary block off plate just to see if it runs any better. I don't know that this would happen suddenly and cause your initial symptoms, but maybe.

 

fwiw, i had similar symptoms and it ended up being a corroded wiring harness in the fuel injection harness on my '86 22re, similar to this: https://forum.ih8mud.com/threads/a-2...-i-had.311436/

 

Thanks for the ideas. Worth checking, though it will be a few days before I can get to it. Rain & maybe snow predicted this weekend, and I don't have an inside place to work.