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3.9V8 Ignition System Fault Finding.


gti-90

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hello.

first time for me posting in the range rover forum.

i have a 3.9v8 out of a range rover in my ex 2.5n/a 90. it was in a 90 before i got my mitts on it..

problem i have is it wont start.

new genuine rotor cap,

new gen dizzy cap,

new bosch coil

new gen ignition amp (the side of the coil type.)

good battery 12v

good starter.

when i go through the haynes RR manual Electronic ignition system - fault finding

i have 12v at either side of the coil with ignition on from + and - from battery.

but with the ignition off i should be reading zero volts at the - ignition coil side with the battery + on the other side of the voltmeter but i get 12..... can any body suggest why this is? ive double and triple checked the wiring and cant seem to find where im going wrong. i have a good earth from back of passenger side of block to chassis and front pssngr side to chassis.

it will turn over and over. fuel pump is pressurised and fuel passing through and returning.

something simple? hope so.

thanks for any replies jack.

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hi. yes its a hotwire 88 onwards.

nige, this is with a brand new one on now no change, last week i got a blue boxed one for free also new but no different . and no diferent from the original 2 pin.

i have 12volts at coil when i shouldnt from battery positive thro multimeter with ignition off. ignition on i have no volts.. and cranking im get 8 to 9 volts on either side of the coil. i cant fiigure it out.

thanks cynic-al i have had a look thro in the past. aslong as a many things google and the such searching can provide.

the plugs look whiteish to me. no fuel getting thro for sure but the fuel is going round via pump. so the injectors can t be getting a pulse?

stumped...

thanks again.

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Don't fully understand what you mean with the coil voltage, but have you tried to check if you have a spark? The old remove plug, hold it against the block (with a good insulator...) and crank the engine.

If you have a spark, do you have good fuel pressure? On my old V8 I had a similar problem, engine turned, fuel was circulating ( squirted out quite well) but when I borrowed a manometer, no real pressure. New pump cured all.

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smallfry. just installed in this vehicle. but has been stood for a while. ive not had it running.

Alsace_rangie. its a brand new bearmach pump, with the pipe and bracket extended to reach bottom of 90 tank. it does seem good pressure, squirts out all over me.

yes i have tried the old spark trick. got a very weak spark even in the darkened workshop.

thanks

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Common mistake is to get the fuel feed and return hoses the wrong way round on the engine.

A weak spark ? Are you running the ignition coil through some sort of ballast or resistor

Its a very long time since I have played with a pre TDi electrical system, but I seem to remember that on the back of the ignition switch on the column, there is a terminal that gives 12v FROM the switch when the key is off, but cuts out when the ignition i turned on.

I might be thinking of an old 2.5 petrol though, but I dont know where you are getting your feeds from so it might be worth checking ?

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hi, coming back to this. ive had a hour on it today so far.

going through the tests that cynic-al posted up. which i had looked at before a while ago and completly forgot. the ((3.9 hotwire system diagnostic tests))

tests 1-7 all fine

test 8 i get 12 volts which is ok. but get 6.2 instead of 6.8kohms? problem?

test 9 and 10 im reading 0.00 on both banks. not the 4-5ohms suggested. but cant find a break in wires etc. all connectors in ok...

test 11 fuel temp thermistor not sure what it should be but getting 3.80 ohms....

test 12 coolant temp thermistor 4.62ohms....

test 13 and 14 when i switch the ignition of, this bypass valve makes a strange vibrating kind of noise? reading of 0.05 on both tests. faulty valve?

test 15 reading 4.25 should be 5000.

test 16 flap closed i get 0v open i get 0.03v, hmm..

test 17 air flow sensor i read 0.01 should be 0.3 to 0.6

i havnt got any further as dont have a pressure gauge etc. but can any body point me in any directions to the above?

thanks.

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  • 2 weeks later...

me again... dont worry theres new news..

it starts.. :i-m_so_happy: . vroooom vroooom.

i checked every wire etc etc. i had the wiring wrong on the ignition switch that wasnt helping. :blush:

but i stil cant figure out why on the rave test sheet. test 3 amplifier switching im getting 12 volts at coil with ignition off when i should get 0. i have found another post on another forum with the same problems and it was a broken earth wire within the loom. the continuity tests i have done show no breaks..

going back to the starting.. its starts but as soon as it does its revving and revving up quite alot. no rev counter but its not idle. its not pulsing revs just brrrrrrrr. any ideas folks?

thanks for the replies so far realy helped me.

jack.

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hello, two steps forward and three back...

got the revving up sorted.

next problem. on startup and leaving it run for maybe a minute, water... about half a cup maybe more from the exhaust end and as black as soot. no oil though or any sign of oil/water mix.

the landrover has not seen the outside world for years so no chance of rain in exhaust etc.

the level in header tank has dropped slightly and when running the water in tank not "bubbling" but moving.. ?

head gasket? as said before its sat for a while. would it be best to whip the heads off and have a look? anything in particular to look out for? ive done a 300tdi before but not a 8.

thanks.

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If you have been trying to get it running with lots of stopping and starting without it getting really warmed up it is quite likely that it is just water from combustion collecting in the muffler. If you have coolant loss after giving it a good run then look into other causes.

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  • 6 months later...

ahh great stuf, thanks again.

Hi Jack I'm wondering how u got on with your issue as I'm now having the same problem with my disco as u had, "but with the ignition off i should be reading zero volts at the - ignition coil side with the battery + on the other side of the voltmeter but i get 12..... can any body suggest why this is? ive double and triple checked the wiring and cant seem to find where im going wrong. i have a good earth from back of passenger side of block to chassis and front pssngr side to chassis"

So, No spark from the coil but Rave tests other as u found above are ok, resistances from coil and dizzy are also ok also, so any help u can give....

Thank you

Peter

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  • 1 year later...

I have the same problem...

but with the ignition off i should be reading zero volts at the - ignition coil side with the battery + on the other side of the voltmeter but i get 12..... can any body suggest why this is?

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