Greetings from down under I have 2 XJ's a 96 and a 99 so I know a little about the 4 liter But I am not a mechanic I recently refreshed the 99 and got it back on the road But it is acting Weird?
Firstly I have replaced the fuel pump and cleaned the tank the fuel rail has been cleaned and Bosch 4 hole injectors fitted
New crank cam map tps iac and front temp sensor New coil dizzy rotor leads and plugs and the cooling system has been replaced The PCM was reset when the injectors were fitted So it should be great?
Oh yes I also replaced the solenoid purge valve and still haven't got a jeep magnet from rockauto.
All of this was done in the last 500 kilometers You hit the key and it starts up straight away no cranking needed idles perfectly drives great the overhead console tells me that I get 11.4 per 100 kilometers temp is fine oil press and volts are good once it warms up and you are at highway speed 100kph/60mph it cuts out develops flat spots surges it never looks like it is going to stall it plays up then it comes good then plays up again?
The last time I checked the fuel pressure was fine I really cant figure this out?
The 99 runs beautiful until you go for a long drive there are no issues around town hardly gets hot as its a small country town .
The only thing I can come up with is heat soak? I don't know much about it I thought it happens after you stop and try to restart? Would it happen while you are driving along? Now the 99 has that stupid box thing on top of the throttle body and the lining under the hood That would have to help keep the heat in?
Should I insulate the fuel rail and injectors and get rid of the hood lining ?
Any ideas

 

MIL light on? Any error codes? What OBD tester do you have? Can you collect live data from the sensors? Monitor vacuum?

10-4 on heat soak that's a starting problem.

This problem started after you put all the new stuff in?

CKS is Mopar?

 

no cel yes just started happening since refresh it was sitting for years previously all the sensors are standard motor parts t series yes heat soak is when you stop i meant vapor lock only thing I can think of?

 

Does it act out if you simply raise the RPM to the above cruising problem RPM while stationary?

I understand Bush People all drive crazy vehicles so this shouldn't draw too much attention:

Take the hood off and drive around. Monitor fuel pressure while doing this.

Periodically release the Schrader valve on the fuel rail to see if air has accumulated. Check all the injector O-rings for damage or leaks (the ones on the head. The ones in the fuel rail would leak like a sieve if they were faulty.). Check for vacuum leaks on/near anything you replaced. Monitor vacuum while driving above and problem repeats.

Consider overheated CKS which can create issues w/o triggering error codes (IMO cylinder failures will trigger a 300 code, even if it's only briefly). No real way to check that in an intermittent failure w/o o-scope (which I would loan you if you weren't on the other side of the planet. Although they're not terribly expensive to get setup if you get really stuck).

So to be clear-- did it EVER run smoothly before all these new parts?

 

Also check the crank sensor and the cam position sensor, these MUST be MOPAR only nothing else. If not Mopar change them and report back . Get them from the bone yard if you have to but chuck the aftermarket stuff.

 

finally got a code off it p102 its a bad number 1 injector i did some tests and it only pulses intermittently i just put a new set of 4 hole in it and one was dodgy oh well at least i now know