when my failsafe light comes on, usually on acceleration,the car shudders for a split second,like youve just dabbed the brakes,this can go on every time I accelerate until the RP warning comes up,any ideas?
I know I will be told to get the codes read but until I can either afford a good code reader or pay extortionate dealer prices I just wondered if anyone might have a clue to whats going on?
ive cleaned the TB,checked for splits in the "concertina" air duct,cleaned the maf,etc, dont know what else to do.
the hesitation in acceleration is frankly dangerous and I wondered if this was a cause or symptom of the failsafe warning.
would a dirty fuel filter cause this?

 

Here in the states, Autozone and several other major auto parts stores will read one's codes for free... is there nothing like this service available in England?

Does your Check Engine light come on also? Unless this occurs, there will be no codes stored.

 

I like Quad suggest that you get the codes, if not you will be chasing a ghost. What year and model is your car? We have several posts on this subject and would suggest reviewing them for other possibilities. On the most part Restricted Performance is related to intake leaks, Throttle Body (plugs), MAFS, Clogged Breather Stub and a few others. Go to the FAQ https://www.jaguarforums.com/forum/s...ad.php?t=20090 and read a little before moving on.

 

Sorry,should have said,its a 1998 xj8 sovereign 4.0L, unfortunately I don't believe we have anywhere in the UK that will read codes other than going to a dealer or specialist independent.
I think what concerns me most is the hesitation during acceleration, feels to me like either a fuel fault or electrical,ie,ignition

 

QM,no,I dont get a check engine light come up, does this mean its a waste of time reading the codes?

 

No check eng light then you may not have a fault. If your car is hesitates it may be due for a tune-up or that you need to run a fuel cleaner to clean the injectors. It could be the throttle body or the plugs to it but I would try both tune-up and fuel additive if it hasn’t been done for a long time. Fuel presentation and proper firing is important.

 

Gus,I put a bottle of STP injector cleaner in the tank only yesterday,perhaps it takes a while to work through, I had the same problem while driving today,probably only 50 miles after adding the STP

 

Do you know if this TB Service Action was done? http://www.xclusively-jaguar.co.uk/xj04_fandi.html#5

 

not so far as I know,certainly not while in my ownership (since last December)thanks for the heads up though, I have to say though,it doesn't cut out completely,only momentarily ie, maybe for one second,and only on acceleration,but that's enough to trigger the failsafe light.

 

I had a throttle body issue, in which I would only get restricted performance/fail safe modes with no codes thrown, until they became so prevalent that a power down/ restart would not fix it... then it finally threw a code and CE light.

I was seeing both an occasional hesitation on acceleration and a more prevalent throttle modulation without any throttle input on my part, especially when at idle, moving slowly, as in a parking lot; the car would try to accelerate - followed shortly by the error messages on the display. This occurred more often on wet or humid days. The code thrown pointed to Throttle Position Sensor signal out of range.

I traced it to a poor connection due to the dissimilar metals used in the Throttle Position Sensor's connectors - gold in the TPS and tin plate in the mating connector. There is also a TSB on this issue. The dissimilar metals cause galvanic corrosion to form on the connector pins causing an occasional intermittent connection.

I simply cleaned all the connector pins, both in the TPS and the mating harness connector with spray-on contact cleaner/lubricant, in my case from Radio Shack, while plugging and unplugging the connector many times - to remove any corrosion. Haven't had a problem in the 3 months since.

 

Quad I think you are right on.

I was going to mention this but hesitated, it did not fall under that year but should be looked at. http://www.gusglikas.com/AutoRepTB.htm

 

Ah, yes... I see that the TSB was for 99-01 4.0's... but, even if the dissimilar metals is not the issue, moisture leaking into the connector past a failed seal might still cause the same kind of problem with the same solution - cleaning... worth a try? It's a very simple procedure.

 

Well, I've spent the morning cleaning every contact and electrical plug I can find that has anything to do with the MAF, TB, and injectors, I've also taped up every conceivable pipe, pipe connectors and joints that could possibly leak.
Ive just come back from taking the ol' girl for a spin around town and I have to say she ran flawlessly,so far so good.
I know its early days yet , I know that every squirt of the throttle could bring on the dreaded Failsafe but the car was built to be used and enjoyed so that's what I intend to do!

 

Hope you found and fixed it... only trouble with doing so many things at once is, if it ever pops up again, you won't know which was the cause, lol. Good luck!

 

Kudos to you! Hope it stays that way.