Just how smooth should a 88 2.9 run?

[Hitchner2009]

You said you had yellow spark before you changed the coil? The 2.9L runs on a distributor not coil(s). Yellow spark is caused by a loss of voltage to the plugs, you want blue spark. I would recommend replacing your distributor cap and rotor and applying some dielectric grease to the plug connectors.

Also, i know this may sound stupid. But have you checked to make sure your spark plugs are in the right order, meaning they are on the distributor cap correctly and on the plugs themselves correctly? It can be easy to misroute one or two of the wires and cause a stutter and make you wonder what it could be. Check for any vacuum leaks as well around the intake, spray some brake cleaner around the engine bay and listen for changes in engine rpm. If you find a spot that changes the rpm when you spray that area, search for cracks, tears or anything of the sort.

 

[scottveazie]

Confirmed my firing order was correct, popped the cap and rotor and it had corrosion on it, I cleaned it off with my dremel, but I noticed the center graphite contact had a groove in it? Still runs rough to me when cold, better when warm but I feel it should be smoother? Took some video but have no idea how to upload it.


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[scottveazie]

I also have the firing order according to the picture I found online for 2.9 firing order.


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[scottveazie]

New cap and rotor, no change. Shakes in gear cold, gets better warm. Does each cylinder have it's own injector? Also unplugging the fpr makes no difference but it's not smelling of gas, or acting like a bad fpr.


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[RonD]

Yes, each cylinder has it's own injector but the '88 2.9l uses Batch Fire fuel injection, on a V6 that would mean 3 injectors open at the same time, then the other 3 open at next firing.
This keeps intake full of fuel/air mix(like a carb did) so a single misfire probably won't be fuel related.
But I run a can of Seafoam in the gas tank once a year to keep my '94 4.0l idle smoother, it is Batch Fire as well.

If you have a shake at cold idle I would try to ID if it is just one cylinder doing it.
Unhook one spark plug wire and start engine, if miss is worse turn off engine and move to next spark plug wire.
If shake doesn't get worse with one wire unhooked then there is just one cylinder causing this.

A vacuum leak between intake and head near that 1 cylinder can cause it to have a lean mix and misfire when cold, and then as engine/metal heats up it expands, restricting the amount of air coming in and leak has less of an effect.

A worn out valve guide seal can add a bit of oil to a cylinder's fuel/air mix, this makes the mix harder to ignite, especially when cold.
Oil burning in cylinders can be seen on the spark plug tips, pull all spark plugs and keep track of which cylinders they came from, then look at them side by side and see what they tell you about how the cylinders are running.
Google: spark plug condition

On a cold engine compression is what allows an engine to start.
A spark will not ignite a fuel/air mix at any temperature, contrary to what you may have seen in Hollywood movies, lol.
The compression heats up the fuel/air mix so a spark can ignite it, once cylinder warms up then compression is not as critical, so a lower compression cylinder would "fire" normally once engine heats up.

A compression test on all cylinders may ID an issue
All spark plugs removed
Throttle plate open, hold gas pedal down all the way, this also cuts off fuel injectors
Compression meter in one cylinder
Crank engine until you hear 4 "hits", compression strokes in that one cylinder
Write down results and cylinder number

Repeat for all cylinders

What you are looking for is, at most, a 10% difference in all cylinders, usual compression is in the 150-180psi range.
When a cylinder is below 110psi if would be iffy to get it to fire cold.


Spark plug gaps are important but are set for longest life on untuned engine.
Larger gap will create a stronger spark, this is better for cold starts and low RPM operation but not as good for high RPM operation.
Smaller gap is a weaker spark but will give better high RPM performance.

The Factory recommended gap can be adjusted up to 0.01 in either direction for your driving habits
Or to help with a cylinder misfire issue.
Factory spec for the 2.9l is 0.044 gap
If you can ID which cylinder is causing the misfire try a gap of 0.50 and then 0.054 if that doesn't help.
A larger gap can allow firing at lower compression and with a little oil added.
But you will have to remember to regap or replace that plug every few months

Good read here on the 2.9l engines:
http://www.therangerstation.com/tech_library/2_9_Page.shtml

 

[scottveazie]

Small update, thanks so much Ron for the help. Number 1 spark plug was completely oil fouled, the rest were pretty good. I cleaned off the oil and gapped that plug to 0.050. Still rough cold but better, once warmed up much better. I will recheck that plug today and see, I did run seafoam before this so maybe that fouled it out. Also will check for a vacuum leak between the head and intake around number 1.


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