3.0 ignition problems help!!

[mrford60]

I am trying to help a friend fix his 1991 Ranger 3.0 AT 2WD truck 155k miles, it is missing bad on all 6 cylinders. If i put the timing light on all 6 plug wires it will cut out at idle and when i try to rev it and it usally falls on its face. and yes i tried 2 timing lights. we have replaced the cap, rotor, wires, plugs and the pickup in the dist., i have also swapped in a coil, module and computer, and have looked at the wires to all of those. We are stummped, i am ready to put a stick of dynamite under the hood.

 

[lairdt]

I'm fighting a bad miss on my '91 3.0 AT 2WD truck with 80k on a rebuilt engine. When dead cold it usually runs ok, but if you drive 20miles and park it then it really shakes when you fire it up. Already gone through the ignition and everything is new and checks out fine, checked timing, no codes, replaced injectors made no difference, new fuel filter. Engine revs to 5k in park without any problem, but shakes when at idle. Road power seems to be lacking too, especially on minor hills.

Tried to perform the cylinder balance test, but about 3 cyls in it (a guess on my part) makes a loud click, engine almost dies, and it aborts the test without any error.

I'm going to unplug the MAF tomorrow and see how it goes, but your problem sounds more like a plugged cat if it can't rev up.

 

[Rearanger]

...it is missing bad on all 6 cylinders...we have replaced the cap, rotor, wires, plugs and the pickup in the dist., i have also swapped in a coil, module and computer, and have looked at the wires to all of those.

I'd look at vacuum leak (PCV hoses & EGR +) first then fuel. A leak in the intake hose downstream of the MAF will cause engine to miss/stall and idle poorly. Also check TPS (if a 91 has it) for adjustment and proper functioning. Does this occur at cold start only or/and when hot?

I can't explain timing light thing. Don't know why it would have an effect on ignition/idle if inductive pickup is used over the ignition wire. Is it an inductive light?

 

[Rearanger]

When dead cold it usually runs ok, but if you drive 20miles and park it then it really shakes when you fire it up.

That's usually an indication of malfunctioning engine coolant temp sensor (ECT) that causes engine to run too rich when hot. Are the plugs black? Is there black smoke coming from exhaust when engine hot?

Tried to perform the cylinder balance test, but about 3 cyls in it (a guess on my part) makes a loud click, engine almost dies, and it aborts the test without any error.

Do you mean you disconnected one spark plug wire at a time and listened for uneven change in engine rpm?

 

[mrford60]

it will rev up, but you cannot floor it you have to do it gently, we had taken out the converter to try that before we found the problem with the spark cutting out. with the timing light on it you can watch the light cut out every once in a wile at idle and when it dose the engine shakes (on all 6 wires) yes its a inductive light, but it will do it more when you can get it to rev up. the plugs are black but i am thinking that it is from the spark cutting out.

 

[Airmaster]

Damn, if you are sure on the wires and plugs and stuff it's gotta be the engine sensors...

Well, I'll list off the things it could be from the haynes manual...

Spark Plugs, Spark Plug Gap
Fault in fuel or electrical system
Faulty Spark Plug Wires
Vacuum leaks at the air intake
Uneven and/or low cylinder compression
Fuel filter clogged
Faulty emissions components
Faulty ignition

 

[lairdt]

That's usually an indication of malfunctioning engine coolant temp sensor (ECT) that causes engine to run too rich when hot. Are the plugs black? Is there black smoke coming from exhaust when engine hot?

Do you mean you disconnected one spark plug wire at a time and listened for uneven change in engine rpm?

Spent more time on it over the last several days. I had only been driving in to work mostly before, but found that when cold this morning it started up with minor miss but when I turned it off within 2 min of cold start and restarted it, it had a severe miss that cleared up after a bit... Then settled into the "regular" miss. No smoke at any time.

I've swapped coils, ignition module (on radiator post), plugs (again), wires (again), and MAF. Problem persists and didn't change any with these single tests.

Cyl balance test, as in the built in test in the EEC-IV. Pulled plugs, all had 500 miles on them and were nice and clean. I did pull individual plug wires from distributor this morning, and all but one made it shake quite a bit. Pulling #5 didn't seem to make as much of a difference. I wonder if #5 injector is bad or bad connector/wire... ??

Guess I need to do compression check and see if I hit the 160psi expected.

 

[lairdt]

Compression check out ok, guess it must be injector related...

 

[mrford60]

i found three problems, the replacment maf was bad, the thermostat is stuck open not getting enough heat and the plugs were fouled (because of the maf and running to cold). already replaced the plugs and the maf, it runs great cold, but havent replaced the stat yet.

 

[mrford60]

all better thanks