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Mpi With Ignition Issues


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#1 NealinUSA

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Posted 27 January 2021 - 07:38 PM

I have a '97 MPI with ignition issues. The engine will not start, or  if it starts it will not run for very long. This is a general timeline of the failure.  For about a year after I purchased the car it ran fine then one day after a quick trip to the shops it would not start when i went to put away for the evening. I shoved  it into the warehouse with the plan of looking at it later. About a month later I went to go and work on it and the car started without any problem. So I drove it for about a month and the same thing happened again. I push it into the warehouse. This time I only waited a week before I started to work on it. This time it ran for about 5 minutes before it stalled. The car has approximately 78k miles on so  I decided it might need a new coil pack. This did not get the car to start so I installed a new crank position sensor. Still no joy. The next step was to purchase a Pscan ECU reader to see if there were any codes present. Nothing other than oil temp and ambient air temp and we know those don't mean anything. I know the fault is in the ignition system somewhere because early on in testing I would hook up my inductive timing light to the  #1 plug lead. If the timing light flashed the car starts and runs as soon as the light stops flashing....... So the car has a brand new battery, new coil pack, new crank position sensor, the bulkhead to engine mount ground is tight, the four 30 amp fuses are in good condition, and there is fresh fuel in the tank. To start the car I press the imobiliser  key fob. The light goes out and i hear the little relay behind the dash click in. I turn the key to position two. I hear the fuel pump prime. I engage the starter and the engine will cough with a couple of flashes from the timing light and then nothing. It will continue to crank but no spark. Now I know (in my heart of hearts) that if I leave the car sitting for another month it will probably spring to life for about  a minute or two before going dormant again. My gut says ECU issues but any input would be really welcome.



#2 Wazzah

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Posted 27 January 2021 - 08:17 PM

I had a problem with the common sensor earth circuit which would be pin 13 on your ECU.

I disconnected all the sensors ( Coolant, Air Temp, TPS and in your case the MAP) and the car started presumably in limp mode.

I had just rebuilt my motor and had all new sensors.

As the car was running I plugged a sensor at a time back in and it stopped when I reconnected the coolant sensor.

Changed the new coolant sensor for an old one and the car hasn't missed a beat since.

MEMS must pick up on weird voltages at pin 13 (Pin 30 on my SPI) and throw a wobbly.

Give the disconnect reconnect thing a try as it costs you nothing.

Regards Waz



#3 RedRuby

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Posted 27 January 2021 - 10:35 PM

I had an intermittent problem with starting which eventually turned out to be with one of the relays in the auxiliary relay module on the brake servo. Mine was caused by water damage to the starter relay so I got no cranking at all. So different to you but it may be one of the other relays in the pack is causing your problem.



#4 Steve220

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Posted 28 January 2021 - 09:41 AM

As RedRuby mentions, worth checking over the relay pack. See if any of the prongs on the plug look a little burnt or signs of getting warm. Also worth replacing your fuel filter. MPi's don't like to be starved of fuel.



#5 NealinUSA

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Posted 28 January 2021 - 04:30 PM

Thanks for the replies guys. It is unlikely to be the fuel filter as that was changed a little over a year ago.  But the other stuff is all worth a go. Do you know if the relays are interchangeable? 



#6 NealinUSA

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Posted 28 January 2021 - 07:43 PM

Waz, are you thinking that an under/over volt on the  Coolant, Air Temp, TPS and MAP sensors  would cause the EMCU to open the main relay in the MEMS relay box and thus depower the Coil pack? Could the the MEMS relay be another potential fault area?



#7 FlyingScot

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Posted 30 January 2021 - 11:39 AM

Intermittent faults are always fun...

I would start with the basics, which it sounds like you have except battery voltage.

MEMS doesn’t like low voltage so I would run this out before checking earth points and also see that the alternator output is correct when it briefly does run.

After that it’s sensors crank and cam if it’s a MPi (and not a JDM car which is MPi block with SPi injection)

 

FS






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