EGR -vs Non-EGR 4.0

[RustyMacintosh]

First, I am a new member. I own a 1994 XLT loaded 4x4 Explorer with lots and lots of miles. BUT is very nice condition. Just dropped a new trannie in it. New radiator last weekend, never could get the fan clutch to come loose but it is working.

Mornings, it misfires on #6 for a spell, maybe 2-3 minutes at idle, then it clears up to a smooth idle. IT IS not exchanging any fluids. IT uses no oil, no anti freeze, nor does the exhaust smell when cold of anti freeze.

It does not overheat. But like I said it has a ton of miles on it. 265K.

I can get from a salvage yard a 88k complete motor. But it is a NON EGR motor. Mine is EGR. Since we are reg'd in a county of California that does not smog each year, I am not worried about that aspect.

If I bought it, other than plugging the exhaust manifold, (unless the complete motor has a non egr exhaust manifold), will the ECM run the motor as usual?

No issues?

As for the misfire, someone did say it could be a weak EGR. You can feel it smooth out like something just changed in the motor when idling at 1000 rpm's. I thought for a while it was an injector, but this is too consistent.

Fire it up cold, it misfires, then smooths out within a couple of minutes as if a vacuum or sensor closes, or opens, but everything is new. TPS, the vacuum connection on the intake related to the EGR, MAF, and has a 190 thermostat.

 

[410Fortune]

if you have a misfire, you have a misfire. They do not usually "go away" it is just not as obvious at higher rpm
Yes you can install any 4.0 longblock in there from 94-2001 if you know a few things.
The 4.0 pushrod was run from 1990-2001
To repower your 94 I would try to get as low miles and late year engine as I could
The heads after 1995 are much better
The 98+ uses an 8 bolt crank, earlier used 6. So to put a 98 or later engine in just make sure you have the correct 8 bolt flexplate that comes w your new engine

The engine itself changed very little from 90-2001.
You can add or remove EGR as needed, the EGR plumbing and controls go with the truck. If your 94 has EGR then you can add the EGR to the non egr engine. This is just plumbing and your 94 PCM is expecting it

When changing engines basically you will strip the new block down to the lower intake and install it, then use all the "dressing: from your 94 block...essentially changing whatever year 4.0 you install into a 94 4.0. With a misfire on cyl 6 I would clean and test each injector before installing them into the new engine.......

 

[RustyMacintosh]

it is interesting that after a minute of miss-firing on #6, it goes smooth at an idle, you can put your hand on the exhaust it is smooth, no puffing.

I was aware that the heads tend to crack. I'm going to do a compression check on #6 before it fires then after warmed up to see if it is in that area or something else. It sure ass heck feels like a vacuum leak somewhere.

 

[410Fortune]

Its probably coolant in cyl 6
What does the spark plug look like?
They don't just crack you get hairline fractures and gasket leaks. Cyl is wet when you first fire it up and then it burns off, but it is always still there just not as obvious.

Could also be lower intake manifold, can be a valve guide seal, can be a bad injector, but with a older 4.0 its usually a head gasket issue.
Do you get computer code telling you misfire?
You are smart to try and identify the issue now or while the engine is out, that way you know you will fix it with the engine replacement/are doing the right thing

 

[RustyMacintosh]

no codes
no check engine lite
no use of anti freeze
no use of oil
no overheating

have not pulled the plug cold to see what it looks like or compression,

it has 242k on the engine
am buying an 88k motor complete to swap in
but until then,,,,

the interesting aspect, is the misfire goes away within a few seconds when semi warm, nothing when warmed up, cold it lasts maybe 30 seconds or more then gone...smooth from then on