Electric or ignition problem
Discussion
Hi, having problems with my 1994 griff 500HC , it started playing up a couple of weeks ago , the engine died whilst driving , when i stopped and restarted the speedo shot up to max mph and car started misfiring ,, i left it a couple of mins and it started ok and was ok all day. Then last week it kept stalling when i stopped at junctions and when i restarted , the speedo moved with the rev counter even though i was stationary.. Checked and cleaned speed sender on prop shaft. Speedo registers correct speed when moving, could this be a problem with the speed calibration box behind dash,, not keen on taking dash out unless have to as its a fiddly job,,,
Any ideas appreciated
Any ideas appreciated
Wierd ...I dont think he rev counter input goes nowhere near the speedo calibration box- so if both gauges are bouncing around together the only common point is the ground- The speedo calibration box could only produce a misfire if its speed signal went high enough to trigger the speed limiter in the ECU (if its enabled that is on the TVR mapping that is). Together the fault would look like the ground side of the dash was being spiked by the ignition pulse- so start with your earth and revcounter connections Id say.......
On my Chim last week, as the battery was dying, I had similar weird things happening. Ignition on engine not running, trying to start the car drained the battery and rev counter jumped up to 3000 and then died to zero slowly, speedo jumped up to 20 and back to zero. Maybe a check of your battery is in order as its quite simple to do and if its on its way out it coulkd save a lot of detective work. HTH
Today i removed dash and heater switch panel,, all wiring looks ok , found speedo calibration box hanging from loom,, all connections look ok,, earth points on top of tunnel look good , cleaned them just in case,, engine starts ok , will have to drive it on a run to really test it,,, now trying to get heater panel nuts back on through window switch holes,,, may have to remove centre console completely ,,, what a pain ,,, thanks for all the suggestions,,,
with Matts help we used the ECU-mate to check the ECU and found on IDLE CONTROL with the engine running and car stationary
ROAD BOX A/C IDL POS
Fast === === === 95
when we checked another Griff instead of Fast it said Stop
im guessing the ECU is seeing the wrong signal from the Speed Converter Box and thinks the car is moving.
Is this correct , no wonder my idle drops too low when stationary. so its the convertor box or wiring fault
ROAD BOX A/C IDL POS
Fast === === === 95
when we checked another Griff instead of Fast it said Stop
im guessing the ECU is seeing the wrong signal from the Speed Converter Box and thinks the car is moving.
Is this correct , no wonder my idle drops too low when stationary. so its the convertor box or wiring fault
waggy said:
with Matts help we used the ECU-mate to check the ECU and found on IDLE CONTROL with the engine running and car stationary
ROAD BOX A/C IDL POS
Fast === === === 95
when we checked another Griff instead of Fast it said Stop
im guessing the ECU is seeing the wrong signal from the Speed Converter Box and thinks the car is moving.
Is this correct , no wonder my idle drops too low when stationary. so its the convertor box or wiring fault
The speed control box has a couple of inputs from the diff sensor, and basically when one input starts to pulse it generates the speed signal for the ECU. Problems occur because both inputs are near 0 volts when the car is still, but a small voltage on the Earth input causes the comparitor chip to think there is a signal from the diff, when its just electrical noise. "TVR mike" came up with a modification some time ago where a couple of resistors pull the comparitor input up by .7 of a volt or so before it starts to switch, so its less noise prone. Also one unit I looked at has a very poor solder joint on the connector to PCB, and effectively the earth was simply floating on the PCB, so the connector simply needed re soldering. I dont think there is an issue if every earth (or the earth path ) between the back of the PCB and the diff sensor is clean, but Mike pointed out there in an earth strap around one of the front wings that can corrode.ROAD BOX A/C IDL POS
Fast === === === 95
when we checked another Griff instead of Fast it said Stop
im guessing the ECU is seeing the wrong signal from the Speed Converter Box and thinks the car is moving.
Is this correct , no wonder my idle drops too low when stationary. so its the convertor box or wiring fault
Thanks Mark , theres definately a connection problem, i opened the speedo converter box and all connections look ok , i also cleaned the terminals on the box , i drove the car today and when the engine got hot it started running rough on idle and when i revved it whilst stopped at a junction the speedo moved in unison with the tacho , The speedo works perfectly on the move, if i rev the engine whilst driving the speedo is ok and stays at the correct speed. Could be the pulses from the speed senser is stronger than the signal its getting from the tacho . I think the problem must be a short between the tacho and speedo in the harness somewhere,, trouble is the harness is hidden behind the dash and centre console ,,, thanks for all your help ,,, alex
Which gearbox do you have? with a Rover box you will have a separate trigger off the box to the ECU & one off the diff for the speedo for circa 1994.
I'd check the dash earthing (std just in front of the gear lever by your left knee or the other side body bolt) and the alternator sense (which can push too high voltage back down the dash live circuit ~ just pull the small connector off the back of the alt to test) first.
I'd check the dash earthing (std just in front of the gear lever by your left knee or the other side body bolt) and the alternator sense (which can push too high voltage back down the dash live circuit ~ just pull the small connector off the back of the alt to test) first.
Its an early 500HC preserp with T5 gearbox , wiring is different to other 500HC , it hasnt got a 100a fuse , alternator is connected direct to starter and the wiring in the passenger footwell is different . tried to fit a hotstart kit and none of the connections exist, back to the problem ive already cleaned the dash earth by the drivers door handle ,, cleaned the speed sender terminals on diff . Need to trace wiring from speedo and tach as they seem to be shorting somewhere,,, this problem started when i got caught in heavy rain a couple of weeks ago,, maybe water got into a connection and shorting somewhere,, does the wiring for the speed sender on the diff run under the car. Will get under car and check all terminals,,, thanks for help,,,
blitzracing said:
The speed control box has a couple of inputs from the diff sensor, and basically when one input starts to pulse it generates the speed signal for the ECU. Problems occur because both inputs are near 0 volts when the car is still, but a small voltage on the Earth input causes the comparitor chip to think there is a signal from the diff, when its just electrical noise. "TVR mike" came up with a modification some time ago where a couple of resistors pull the comparitor input up by .7 of a volt or so before it starts to switch, so its less noise prone. Also one unit I looked at has a very poor solder joint on the connector to PCB, and effectively the earth was simply floating on the PCB, so the connector simply needed re soldering. I dont think there is an issue if every earth (or the earth path ) between the back of the PCB and the diff sensor is clean, but Mike pointed out there in an earth strap around one of the front wings that can corrode.
Rather find the fault than alter things. Ive owned car for 9 years and this is the first time this has happened. I think water has got into the wiring after i drove it 30 miles in a downpour. The next time i used it , The engine died on me whilst i was driving at 40mph , when it restarted it was mifiring and the speedo went to max mph and stayed there. I checked all the connections under the bonnet , MAF, coil , plug leads etc and it then restarted ok , i drove it 60 miles ok . Then a week later i used it and it kept stalling at junctions and i noticed the speedo was moving with the tacho, i will continue to check all the wiring and connections and have a look under car as could be speed sender wiring earthing out,,i will also check the earth under the wing behind offside wheel . thanks for the info , ive learned a lot about the ECU and idle control with this fault. I enjoy working on the car and you learn more when it has a problem. Alexwaggy said:
Its an early 500HC preserp with T5 gearbox , wiring is different to other 500HC , it hasnt got a 100a fuse , alternator is connected direct to starter and the wiring in the passenger footwell is different . tried to fit a hotstart kit and none of the connections exist, back to the problem ive already cleaned the dash earth by the drivers door handle ,, cleaned the speed sender terminals on diff . Need to trace wiring from speedo and tach as they seem to be shorting somewhere,,, this problem started when i got caught in heavy rain a couple of weeks ago,, maybe water got into a connection and shorting somewhere,, does the wiring for the speed sender on the diff run under the car. Will get under car and check all terminals,,, thanks for help,,,
You probably have the early system where the fusebox connects to the alternator, and the alt to the starter, starter to battery (even though the battery sits right next to the fusebox there's no direct connection 
). It's the alternator sense / warning light connection I was referring to for diagnosis.The tacho & speedo wiring only comes together against the bulkhead behind the radio, & even then only for @12" of well protected loom before it terminates with the dash multi-connectors + the dash loom tagged to the back of the dash panel. They do however share the same dash +ve & -ve feeds..... (& the positive one is coupled via a LED & resistor to the sense from the alt).
ETA: if its water related take out the AFM and dry it out thoroughly... God! things are so much easier when you bin the 14CUX
Edited by spend on Monday 6th May 22:54
Spend, you seem to have a good knowledge of the wiring , is there any decent diagrams about . the steve heath bible is not very good with the diagrams. i was an electronics engineer before early retirement so am used to tracing faults with diagrams.
The alternator sense wire goes into the loom by the engine and reappears on the dash as the alternator led. it must connect to the speedo/tacho in the loom somewhere... any more info appreciated
The alternator sense wire goes into the loom by the engine and reappears on the dash as the alternator led. it must connect to the speedo/tacho in the loom somewhere... any more info appreciated
waggy said:
The alternator sense wire goes into the loom by the engine and reappears on the dash as the alternator led. it must connect to the speedo/tacho in the loom somewhere... any more info appreciated
The sense wire connects across a LED to the +ve ignition circuit (which supplies ALL the dash instruments except the clock). In parallel with the LED is a resistor so that juice flows to excite/start the alt if the LED fails ~ so the diode is not acting as a gate & the alt could be at a higher alternating voltage than the battery which would cause havoc with your instruments. As I said temporarily disconnecting the sense wire at the alt would enable you to easily check for that, no real drawbacks just the warning LED will be temporarily not working & the alt will excite its own field coils as soon as the revs reach @2000.Did you think the alt had some logical connection to the speedo/ tacho
or have you mixed up the w+ term which is for LR diesels that have no sparks so take a pulse from the alt to drive the tacho? (we don't have diesel engines, or use that terminal even though it is std on the some of the alts ~ odd TVR's though did use it as the ground for the otter switch??????)
Sorry got confused when you said the sense wire connects the power to all the instruments,, i cleaned all connections i could find , removed centre console to clean earths on both sides , removed dash and cleaned all connections ,, took car for a drive and it seems ok , not sure if fault cleared or just intermittant,, will try again with ECUmate at the weekend as it not mine and im seeing him sunday at brooklands TVR day,, cheers Alex
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