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MPI relay schematics?

Kenny_Kline

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Joined
Dec 27, 2007
Messages
789
Location
Seekonk, MA
Long story short, I am having a problem with my MPI relay and/or wiring. I am going to try to put in a new relay and see what that does but in case that doesnt work, I am going to end up testing each wire to figure out what one is making my car act up. My car is not driveable at this time as it needs fuel injectors so running condition is unkown.

Here are the videos that will describe the issues I am having:

First video is with ecu plugged in, mpi relay plugged in, everything plugged in except for fuel pump. Second video is everything plugged in as described but this time, MPI relay unplugged.



 

bazeng

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Feb 6, 2003
Messages
2,520
Location
Melbourne, Australia
I think what you have is some incorrect wiring where you could be possibly feeding a constant power cable to an ignition power cable which is activated by a relay.

So what is happening is basically normal power conditions until you switch that relay on via the key by giving the relay ign, and then it sticks because ign and constant are joined.

That would be my only thought. Unless you have a sticky relay somewhere?!?!
Try disconnecting random relays.

Have you rewired your fuel pump to your battery via a relay? you could check that..
Or try another MPI.

Could your barrel be sticking?

Pain in the ass to trace.
 

Kenny_Kline

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Dec 27, 2007
Messages
789
Location
Seekonk, MA


Incorrect wiring? Its all factory wiring... The fuel pump has been re-wired but I disconnected the relay in the back and disconnected fuel pump power wire from battery to rule that out.

I would try another MPI but I am having no luck finding one.

When you say barrel, do you mean ignition switch where you put the key? If so, then that is working fine as if you shut key off, all lights stay on, disconnect mpi fuse or battery terminal and hook back up then the lights go off so that rules out the ignition switch getting stuck.

Now that I have had time to sit and think about it it could possibly be a sticking relay.

My focus is to get wiring schematics for the MPI relay and test each wire with ignition off, dash lights on so I can see what wires are getting power. I just need schematics and when I find the wire, that will be my answer. I know 1 wire on the MPI relay is going to get a constant feed but all the others should see nothing so once I get schematics for that thing, I am almost positive to find me issue (if not a sticking MPI relay)

Anyone have any schematics or an MPI relay?
 
Last edited:

Kenny_Kline

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Dec 27, 2007
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Seekonk, MA
Found out how to test just in case anyone searches this thread. I think I should have it figured out tomorrow exactly what it is:

mpi1.jpg

mpi2.jpg
 

Kenny_Kline

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Joined
Dec 27, 2007
Messages
789
Location
Seekonk, MA
As I continue to talk to myself...

MPI relay test results

Continuity test:
pin 3-5 0 ohms (spec is approx 95) FAIL!
pin 2-5 124 ohms (spec is approx 95) Fail?
pin 6-7 0 ohms (spec is approx 35) FAIL!
pin 6-8 7.76 ohms with - on pin 6 and + on pin 8. If I put - on pin 8 and + on pin 6, I get 0 ohms (spec is some type of ohm reading only 1 way and not the other) PASS!

Moving on...

Giving pin 6 ground and pin 7 power, continuity test between pin 1 & 4 turn up 0 ohms Giving pin 6 ground and pin 8 power, I get a relay click then I test continuity between pin 2 and pin 4 and get 0 ohms.

I am not electrical engineer but I am pretty sure that I did the test right and from what I can tell, I have atleast a bad MPI relay.

I am going to try a new MPI relay and see what that does.
 
Last edited:

stevep

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Oct 23, 2004
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416
Location
St. Charles, IL USA
Quoting Kenny_Kline:
Found out how to test just in case anyone searches this thread.



In case you didn't notice, that's the 1.8L MPI relay.

On the 2.0L 1G MPI relay the test are:

Connect pin 10 to +12 and pin 8 to Gnd. The relay should click.
You should see +12 at pins 4 and 5.
With the ground disconnected you shouldn't see any voltage at 4 and 5.

Connect pin 9 to +12 and pin 6 to Gnd. The relay should click.
You should have continuity between pins 2 and 3.
With the ground disconnected you shouldn't see any continuity between pins 2 and 3.

Connect pin 3 to +12 and pin 7 to Gnd. The relay should click.
You should see +12 at pin 2.
With the ground disconnected you shouldn't see any voltage at 2.
 

Kenny_Kline

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Joined
Dec 27, 2007
Messages
789
Location
Seekonk, MA
Ok so here is the deal. With MPI relay plugged in, turn key on then off, lights stay on on dash, I cut the #8 wire on the MPI relay and the dash lights shut off.

Pin #8 on MPI relay goes to the ECM and according to schematics, it goes to pin #63 & #66 on the ECU. So either the ECU is keeping the MPI relay activated or the wiring from those pins on ECU to MPI relay are shorted to ground keeping the MPI relay activated.

Maybe jump the wires and try that or try another ECU?
 
Last edited:

misterfixit

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Aug 4, 2004
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1,583
Location
Midlands, UK
pretty sure on the dohc cars the relay has 10 pins. sohc cars are 8 pins.

Rich

Quoting Kenny_Kline:
Found out how to test just in case anyone searches this thread. I think I should have it figured out tomorrow exactly what it is:

mpi1.jpg

mpi2.jpg


 

stevep

Well-known member
Joined
Oct 23, 2004
Messages
416
Location
St. Charles, IL USA
Quoting Kenny_Kline:
Ok so here is the deal. With MPI relay plugged in, turn key on then off, lights stay on on dash, I cut the #8 wire on the MPI relay and the dash lights shut off.

Pin #8 on MPI relay goes to the ECM and according to schematics, it goes to pin #63 & #66 on the ECU. So either the ECU is keeping the MPI relay activated or the wiring from those pins on ECU to MPI relay are shorted to ground keeping the MPI relay activated.

Maybe jump the wires and try that or try another ECU?



Did you wait the about 10 seconds for the ECU to turn the MPI relay off after you turned it on with the ignition?
There is a turn off delay before the ECU floats pins 63 and 66.
 
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