93 4.0 death struggle

[liteflop]

i have a 89 bII shell with a 93 rang 4.0, m50d and harness. when im in low range or casualy driving around town it loads up the plugs all consistantly black, then misses when i try to exelerate. but idlls perfect,1400cold 900warm. when im racing the motor, pedel to the floor out of every lite and up every ramp{alone in the truk } it seams to clean out and run fine. i ran a computer and no codes and no check engin lite. i borowd a buddys trk whith the same setup and swaped sensors all on top and bottom no change, i even swaped the eec, same. never threw a code. Tested the coil pak its fine, fuel presur and reg is good, fuel filter is new. alt is new,well, new from a bone yard. Tryd new plugs both cheepy champion truck plugs and double plat like the ones required so the electrode doesnt wear from firing twice. What next? I already let the autoparts store dopes talk me into a crank pos sensor fool me once. and i hate to waist any more $ with no results?
When i was driving the donor trk home to do the this swap i noticed it missing, so it did it befor i put it in my bII. Any good ideas or places to look?
Ben Turf

 

[reno]

Smell your exhaust, is it rich? Any smoke, if so what color? Are there any other symptoms (harder to start hot or cold, idles better when warm or cold). What is the condition of your plug wires?

 

[almostclueless]

When i was driving the donor trk home to do the this swap i noticed it missing, so it did it befor i put it in my bII. Any good ideas or places to look?
Ben Turf

That should have been your huge red flag not to proceed.


I'd check the engine compression.

 

[liteflop]

starts better cold but isnt a fight to get it runing warm either. The exhaust smells fine no smoke or oil burning. wires seem in good condition with it running i can hose the motor down and theres no X-firing or bogging. befor i put it in i pulled the heads off and cheked the valves and replaced a bad lifter and rocker sets. ill try to pik up a comp tester but it idles smooth odd compresion makes it idle poorly rite? is it posable for my cat to be restricting too much flo and causing it to burn rich at lo rpm? i put the stock cat back on tryn to keep it as green as posable.

 

[djurs]

The next time you see these symptoms disconnect the MAF sensor plug. If it runs better it means you have a problem with a computer component, as this kicks your truck into open loop operation... Chances are it's MAF sensor if it runs better. It can be cleaned...

 

[reno]

starts better cold but isnt a fight to get it runing warm either. The exhaust smells fine no smoke or oil burning. wires seem in good condition with it running i can hose the motor down and theres no X-firing or bogging. befor i put it in i pulled the heads off and cheked the valves and replaced a bad lifter and rocker sets. ill try to pik up a comp tester but it idles smooth odd compresion makes it idle poorly rite? is it posable for my cat to be restricting too much flo and causing it to burn rich at lo rpm? i put the stock cat back on tryn to keep it as green as posable.

Now wait a minute, did all this happen AFTER you pulled the head? You did pull both heads and check them for straightness right? Do a compression check and at least send a pm to Makg, that guy knows his way around these rangers. Take what I say with a grain of salt, but take to word what MackG says, he got me going in nothing flat. And poor compression would have a little to do with vacuum, your vacuum is from the intake valve opening, but if it is sticking for any reason, then a irratic reading will show.

 

[liteflop]

It was doing it befor i pulled them off. It had a tik thats why i pulled em off i changed a bad lifter and both sets of rockers because the seats where the valvs sit had wor a bit.
Thanks to the engineers i couldent pull the lifters through the heads thats all.

When i unplug the mas is doesnt change but at that point the plugs are already all full of carbon. i tryd to swap a nother one out of a nother truck though and no change so i cleaned my own and stuck it back in

 

[MAKG]

I'd agree that a compression or leakdown test is called for on the donor engine, due to the miss.

I'd suspect grounding issues given that all six plugs are fouling out. Probably accompanied by a lean code. Or else a plugged fuel return line is leading to excessive fuel pressure (easily checked).

Have you run the self tests?

FYI, the sniff-the-exhaust trick works well on a 1966 Mustang, but it only works reliably on a modern vehicle when the engine is cold or cool. A properly working catalytic converter will burn it off, unless it gets overwhelmed.

 

[ttfiveohranger]

I would consider looking at the engine code on the block and make sure you have the right heat range plugs there... all plugs fouling that fast.. and the exhaust isn't smoking? not missing like crazy.. you would notice a rough idle.. Has to be heat range.. wrong plugs maybe open thermostat and the engine not warming up all the way also.. Plugs have to be matched to the engine/heads and running temp of the engine.. If the engine will foul the plugs at idle with out a miss or smelly exhaust that badly? I don't see anything else doing that with everything you've already checked? Know a friend at a shop who can check if its running rich? The engine would have other symptoms in my opinion

Are you putting in the plugs from the sticker to your old motor? get the block and head numbers and make sure you have the right heat range plugs.. I like NGK.

 

[liteflop]

thanks for all the hlp so far. I have to go get a comp tester. I pulled all the plugs and now there not fouled with the new motorcraft doubleplats. there nice and clean with just a little white still all consistant. Come on im not gona put 2.9plugs in and think its all good. I unpluged the mas and ran it 8 miles, it threw a code of mas and still same, a quick miss every 5-10 sec on the hiway not enough to slow you down just enough jerk the truck. How does that loop mode work. At a stoplite it still purrs great. fuel pres is all good 40 with a load 35 at idle or so i tested that first and i rember it was in spec. im gona go look for some ground problems and run a comp test thanks again. Ben

 

[liteflop]

Looks like compresion could be worse it ranged from 145-170,1-155, 2-155, 3-170, 4-145 then i added a spoon of oil and it went up to 155, 5-155, 6-170. is that in a good range i almost hope its not so i can be done chasing my tail. they all were very close around the first comp stroke gauge jumped 80 then the rest of the way. Gunning a long shot, I tryed pinching off the evap line thinking that solnoid may have failed and may be running fuel some how through the tb?? and it ran good for a mile then same shist is that any help or no.. Plugs still look ok when i did the comp test.

 

[reno]

If you added oil and it went up, then that is a indicator of worn rings.

 

[liteflop]

i know that much and if i add a few drops in all the cylinders i bet it would go up all around but is that too much or causing the problem? would that be causing the problem is there a way to cheat it in to running smoother with out pulling the motor?

 

[MAKG]

The ABSOLUTE ONLY WAY you are going to correct a problem with worn rings is to overhaul the engine. There is no cheat.

 

[reno]

Did not mean to imply that you did not know that if you add oil and compression goes up it would be the rings. But if you have a much lower reading on a cylinder (or more than one), and you get a significant increase in pressure, then a ring job is in order. Re do your heads and valves while they are off as well. Clean the carbon off of the pistons while you are there and hone the cylinders, sounds like overkill, but is better to do it now than later.

Like Makg said, there is no cheat nor is there such a thing as a mechanic in a bottle