I'm stumped

[FrankZ1962]

1997 XJ, Sport, AW4
The motor is 4.0 (4.6L Stroker) with approximately 12k since it went in.

I’ve fighting this damn problem for a couple months and I’m completely stumped.

The problem seems rather common, stumbling, hesitation, buck/lurch at speed or from a standing start.

From a standing start and accelerating normally the jeep wants to die, it stumbles really bad and has died on occasion. Restart takes a bit of cranking with the pedal mashed to the floor.

At about 50 mph it will buck and lurch until I mash the gas and get the RPM’s up to about 3k. Generally this starts at about 2k to 2.5K RPM’s.

So here’s a list of the parts that have been replaced after searching here and elsewhere for a solution to this problem. Note that all of these are new within the last 3-6 months.

Fuel pump assy.
TPS
CPS (crank)
CPS (cam)
IAC valve
Distributor
Cap and rotor
Both O2 sensors

A few of the measurements, if it helps:
5VDC into the Crank sensor
5VDC into the Cam sensor
13.6VDC at the fuel pump connector
3.6 and 1.1
Fuel pressure is 49 PSI
Map Sensor output voltage with key on 3.6 and 1.2 at idle

The idle is not steady. It fluctuates between approximately 650-850 RPM.

I’ve even gone as far as replacing the transmission. Yeah I know it sounds nuts but some of the symptoms pointed to faulty shift solenoids and I got the tranny for a great price.

No CEL (OBDII)

So what am I missing?

[AlohaBra]

Have you put it on an ignition scope yet?
(For testing coil and spark plug performance.)
How it the exhaust flow?

[FrankZ1962]

No I've been doing everything in my garage and don't own one.
FWIW the plugs are in great shape with no unusual color. Plug wires are brand new as of 2 days ago.

[AlohaBra]

I am stumped for the moment, maybe someone else can give you an idea soon.

[FrankZ1962]

Thanks for taking the time to read and respond, it is appreciated.

[fredjacksonsan]

Were the problems existing as soon as you did the swap, or did they appear later?

Is this the Golen 4.6? If so, there are 2 things I can think of....first is, have you matched up the intake/exhaust as published for the engine swap? I know they have some parameters to follow for best/advertised performance. Second, if it's a crate engine I'd suggest calling them, to see if there are any suggestions; sometimes on a higher performance engine they have a problem that recurs and is eventually solved by the techs at the company.

[FrankZ1962]

Not a crate motor, I built this one. The problems appeared much later.

[fredjacksonsan]

How about plug wires? You didn't mention replacing them, and I've seen those cause issues.

Also, you may want to check the battery cables. I've had a couple of vehicles that had corroded battery cables on the positive side which caused a reduction in voltage and anything from rough running to not running at all. One of them had corrosion IN the cable, about 6" from the battery so I had to cut open the wire to look.

Hope those help.