tune resistor

[chimalsu]

hi all,on a recent trip my 4.0 hc 96 chimaera cut out after about 50 mile but as i was travelling down hill she bumped back to life and drove faultlessly for another 30 mile to my destination,and the following morning doing the return trip.last week after about 14 mile she cut out again,and restarted after a couple of tries and carried on for a further 3 mile before cutting out again,after a couple of tries restarted and this time only ran for a few hundred yards before cutting out again,this time she would not start and breakdown was required.after a couple of hours the breakdown man arrived tried the engine and started first time only to manage a further 100 yards not to start again so was recovered on a wagon,the following morning car started as usual.putting on rovergauge fault 21 light up -tune resistor,also map 0.i have two questions if anyone can help
a)could this be the cause of the cut outs or is this another problem.
b)where the hell is the tune resistor hidden as i have searched the footwell/batt area i cannot find the dam thing
any advise would be appreciated.cheers alan

[LLantrisant]

mine was underneath the dash.(passenger side, RHD car)...but also my ECU is under the dash....

usually it should be somewhere around the ECU and its loom....so passenger footwhell

its the part with white wires ending in the blue flat connector...left side on pic

[Penelope Stopit]

Take a look at this information https://www.pistonheads.com/gassing/topic.asp?h=0&...

[geeman237]

I had similar symptoms on my Griffith pre cat. Car would run then cut out. It would restart then run for a bit then cut out. It got worse over time. Checked everything, all seemed good. With some help from “blitzracing” on here it turned out to be the ECU gone bad. I bought a used Ranger Rover one off EBay from the day year, swapped the ECU chip out and hey presto no more cutting out. Maybe see if you can borrow someone’s ECU to rule it out.

[blitzracing]

Dont get too worked up on that error, it certainly wont be the root reason the car is cutting out, and as with most diagnostics its possible to get a false lead if you follow it too closely without looking at the bigger picture. What does the rev counter do when it dies? Does it drop instantly as the engine is still turning? If thats the case its loss of spark / ignition causing the issue.

Another one that will do this is debris in the fuel tank that blocks the outlet. This then drops away when the engine stops and floats around again until it next gets sucked into the outlet again and block the fuel again, leading to this random, stop start situation.

Edited by blitzracing on Monday 10th December 13:45

[chimalsu]

hi thanks for the replies.blitz yes the rev counter zeros when it stalls i had a similar problem years ago and a new fuel filter sorted it out,i have bought a new one to put on.i put rovergauge on the car and it comes up as map 0,resetting the ecu doesnt change the map and it shows fault 21,i have searched everywhere in the footwell but cannot find a tune resistor anywhere in the loom,do they put them anywhere else?

[chimalsu]

i found this little blue plug higher up the loom but no resistor,if this is the plug the car has run without one for the last ten year

[blitzracing]

There are some revisions of ECU chip that had the tune resistor disabled, but this was for North America so you cant override the catalyst map, but that would be very odd. The socket looks like the tune resistor one certainly. I thought it defaulted to map 5 without a resistor in there, but I may be wrong- as map 0 is the limp home map. You need to find a 3.9 k resistor and poke it in the holes. As a matter of interest the pins you need are the same size as used on desktop PC power supplies. Event on limp home it wont cause it to die like you have been experiencing however. let me know if you get stuck, I can knock something up.

[chimalsu]

hi blitz thanks for reply,i have ordered the resistor,resetting the ecu does nothing still runs map0,so i must have been running like this since i bought the car years ago,its always idled around 11k but has never really given me any problems,but i obviously dont know what it would drive like in correct mode,so i figured it was worth trying a resistor to see what happens

[chimalsu]

just to add my only fear is someone has removed the resistor previously to mask a different problem in the past

[Belle427]

Probably quite easy to overlook fitting one of these so it may have just never been fitted.

[chimalsu]

tune resistor now fitted,map changed to map 5 from zero,not been able to drive but no noticable difference in running.screen shots of both maps below
map 0

map 5

[blitzracing]

You need to get the engine hot and let it idle for 3 mins to set the long term trim up, or it may shunt badly.

[chimalsu]

engine idled for about ten minutes

[chimalsu]

[blitzracing]

Odd readings- the long term trim shows the engine running rich, yet the sensor readings dont seem a mile out. Worth lifting the lid on the ECU and check what chip is in it- the TVR ones have things like 4.3 cat written on them. I dont have the number retention ti recognise the map off the top of my head...

Edited by blitzracing on Sunday 16th December 11:58

[chimalsu]

hi blitz,thanks for the reply,not had chance to go for not run,salt on road here in derbyshire so she's tucked up until spring.if she's not running right in spring i will try and take it to someone who knows a lot more than me,and resurrect the thread.cheers alan