Hi,
im currently in a slow and long process of finding a issue with my V12 xjs. Especially with a cold engine it runs idle very inconsistent and when using the throttle while driving it sometimes feels like its dying before suddenly picking up. It also stutters a lot at that time. I've checked/replaced:
- checked all the vacuum lines (disconnected the fuel temp switch on rail)
- checked throttle valves on play and setup (installed the teflon spacer to clear play on throttle rods)
- replaced coils
- replaced fuel pump
- replaced ignition with rotor
- replaced leads and spark plus
- replaced fuel pressure regulators

Next stop is checking/cleaning all the injectors and replacing all connectors and hoses.

Anyone some more suggestions since the injectors will be my last option in resolving the issue.

Many thanks for any reply !!!

 

Have you tested the throttle position sensor (TPS)? That can lead to your issues. The TPS should vary resistance smoothly throughout its travel with no jumps or dead spots. It also needs to be adjusted properly for a smooth idle. There are some details on the process in Kirby Palm's BOOK.
Also test for vacuum leaks with a smoke machine. Vacuum leaks will play havoc with the fuel injection.

Jon

 

Hi Jon,
great tips, haven't looked at the TPS yet. But will definitly look into it first thing. Found the topic in Kirbys manual with the values as well. Many thanks.
not sure yet how testing the vacuum with smoke works but will also dive into that.
will post some updates soon.

 

I strongly suggest adding your location to your Sig.

These Marelli cars had different specs for different markets, although the basics stayed the same.

I would be more concerned with:
Spark plugs, age and gapped correctly
HT leads, all 14 of them.
Rotor integrity, bearing in mind the well known Marelli rotor issues.
TPS, already covered.

ALL, and ANY electrical connector. Unplug, CLEAN, replug.
Engine earth straps at and around the LH engine mount bracket. 2 straps involved here.

Injectoirs, nah, I have never had Injector issues on any Infected car, ever.

 

Thanks for the extra info/tips. I have already replaced all leads and sparkplugs with new including the rotor and distributor.
I have not thourogly checked cabling and will do next.

I did however today checked the TPS and at first measurement it went all over the place in resistance from 0.21k to 0.16k and when pressing further it finally became smooth after 0.4kohm. After some searching I found a manual to setup the TPS and is should start from 0.34Vdc tot roughly 5Vdc when connected. I was actually able to set it up at exactly 0.34Vdc when not running and it seemed to be ok.
A testrun learned that now from stand still untill the first 30kmh it responds finally really well. But after 30kmh the issue is still there and even some misfires when trying full throttle. I can only acceleratie really slowly without any fall back in power.
so I assume my TPS is ****ed. Am I correct and should a new TPS resolve many issue or should I still search for some other issues aswell?

 

A new TPS should help, especially if resistance is all over the place during its movement. The ECU gets very confused. I'd definitely start there.
Jon

 

Yes it sounds like the TPS is dud and that a new TPS is in your future!

 

Found a replacement TPS. When it arrives i'll install it and share the results. Thanks for the help so far !!!