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interesting ign problem, carb motor in mpfi


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11 replies to this topic

#1 MilesFox

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Posted 13 July 2004 - 12:14 PM

i got the rx with a carb motor, my secont durbo to carb conversion, but i never had this problem with the first one

when you turn the key, crank, there is no spark till youlet off, sparks once, sometimes if you time it right it will start. i replaced the amplifier(mpfi coil) and that xseemed to fix it. i had the car driven and parked elsewhere for a few weeks, and when i came back to it it did the same thing

if i jump the pos coil terminal to the battery, she will start, and once running, i can pull the jumper wire and she will still run. but if i turn it off or it stalls, it will not fire.

yesterday it just so happened to start by itself, i warmed it up a little and moved iut around. i tried to start it 20 min later and same thing

i may consider a pushbutton momentary button to star6t when cranking(like the jumper) but i also found an accel coil at the yard, and i may eliminate the whole amplifier deal. i noticed the black clip for the ground is not connected to the water pipe on the motor(motor end missing) could that have anything to do with it?

it seems to me that trying to run the mechanical disty('86 carb) with the mpfi coil/amplifier that there is either too much resistance to fire up the coil, or maybe not enough juice? what kind of ideas would you have?

it will misfire once in the upper rpm, coil breaking down. this is the same motor i had in trashwagon 5, but in there it had the shorter blue coil, this time it has the stock mpfi/spfi coil. maybe the resistance value for the coil vs dist is wrong?

the battery was strong after sitting several weeks, it was strong the first time when i got the car together for the first time, battery on the shelf for months

what kind of ideas would you have to eliminate the amplifier. i was going to try with the amplifier disconnected, and rin the pos coil to somewhere hot with the key on(run)

#2 Cougar

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Posted 13 July 2004 - 12:27 PM

I think what is happening is, the ignition is not getting voltage to it when the key is turned to the start position. Have you checked for voltage to the coil while trying to start it? It may be a bad ignition switch causing this. You probably have a test light to check this with.

Since you stated that things run ok once it is started then it sounds to me the grounding question is not a problem. If it was, then it wouldn't run.

#3 MorganM

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Posted 13 July 2004 - 06:37 PM

[quote name='MilesFox']i noticed the black clip for the ground is not connected to the water pipe on the motor(motor end missing) could that have anything to do with it?QUOTE]

Certainly could. If you trace that ground back it goes directly into your ignition system...

Good luck !_!

#4 TomRhere

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Posted 13 July 2004 - 07:51 PM

I concur to the above statements.

Had simular problem 'while back on a Chevy product. Would crank over, no start, 'cept on rare occasions as you let go of the key. Bad contacts in the ignition switch there.

Another car, same senario, just different cause and effect. It was the main battery ground to engine wire that fried-off at the block connection. Car would crank over, (grounded thru small ground wire off battery) just woundn't start all the time, (jumping coil it did, but not by key switch). Took me awhile to find that one, may of had to do with the 12* temps and 30 mph winds at the time. Not to mention the 14" of white stuff I was standing/laying in.

#5 78TurboBrat

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Posted 13 July 2004 - 10:00 PM

Miles, you dont have to wire in a momentary switch, you can just run a wire from the hot wire on the starter solinoid, and then back to the coil, problem solved. you will get power to the coil while cranking, and would have power at the coil, once you let go of the key to the run position. otherwise i would look into the actual key switch after you hook the ground wire back up. just put a new end on it and reattach it to a good ground. then if problem persists, just jumper a wire from the solinoid to the positive side of the coil.

Good luck

#6 Cougar

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Posted 14 July 2004 - 02:03 AM

There is another poster with the same problem also. Doing more research in my manual, be sure to check your fusible links also for a loose connection. One of the green colored links supplies voltage to the ignition relay via fuse #20. Check for voltage at the fuse while cranking the engine. If you have no voltage there then the link is bad or the ignition switch may be the problem.

#7 Humble Nuto 53

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Posted 14 July 2004 - 03:03 AM

had a 240 volvo that did the same thing just before the ignition switch went bad.

ended up using a large safety pin, stabbed through the wires to turn it off and on.....

#8 78TurboBrat

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Posted 14 July 2004 - 10:18 AM

Correction on my part there, you would need to wire in a relay. from the the solinoid, cause if you run it direct, once you start the vehichle, your starter woudlnt disengage, you could even use a ford solinoid to do this with. and just run a hot wire to one side from the battery, and then the other to the coil, then once the car starts and you let go of the key the backfeed of power wouldnt energize your starter solinoid keeping it engaged.

But i still lean towards the switch being the problem.

#9 MorganM

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Posted 14 July 2004 - 11:05 AM

There is another poster with the same problem also. Doing more research in my manual, be sure to check your fusible links also for a loose connection. One of the green colored links supplies voltage to the ignition relay via fuse #20. Check for voltage at the fuse while cranking the engine. If you have no voltage there then the link is bad or the ignition switch may be the problem.


Ya give those links a good tug. Sometimes they can fry a little inside the shielding and arc accross sometimes and not othertimes giving you some funny behavior!

#10 MilesFox

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Posted 14 July 2004 - 12:53 PM

Miles, you dont have to wire in a momentary switch, you can just run a wire from the hot wire on the starter solinoid, and then back to the coil, problem solved. you will get power to the coil while cranking, and would have power at the coil, once you let go of the key to the run position. otherwise i would look into the actual key switch after you hook the ground wire back up. just put a new end on it and reattach it to a good ground. then if problem persists, just jumper a wire from the solinoid to the positive side of the coil.

Good luck


interesting, i'll give that a try. side note: if i jump the coil to the batytery, the car will still run after the key is off and removed! starter tab a good idea, didnt think of that (gt4hire if youre reading pay attention!)

i'll post my progress here tomorrow. so far last night and this morning i didnt have the problem. but i will try that anyway as a contingency fix

#11 gt4hire

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Posted 14 July 2004 - 03:58 PM

interesting, i'll give that a try. side note: if i jump the coil to the batytery, the car will still run after the key is off and removed! starter tab a good idea, didnt think of that (gt4hire if youre reading pay attention!)

i'll post my progress here tomorrow. so far last night and this morning i didnt have the problem. but i will try that anyway as a contingency fix



I am reading and paying attention also. I think we may have the same problem. I believe it may be the switch too, or a loose wire (bad ground) somewhere. I went up under the dash, found the "ignition relay" and have started taking some readings - going by this wiring diagram in a Haynes Manual. The relay is good but the car hasn't acted up in a while for me to check voltages when it craps out. All the voltages are normal except for a question mark on the red/blu wire that goes back to the SPFI Control Unit from the relay. There is 2.75 volts there before the relay engages, (I would think it should be 0v), but then goes to 12.5v when engaged. I don't know if that is normal or not? The other side is fed by a red wire (12v from the fusible links) green link, and then to the battery.

I haven't tried the + coil to the battery thing yet but it this does turn out to be the switch, I might just have to come up with one of those "push-button thingys". Aren't those IG switches pretty expensive? And tough to remove and install? Don't you have to remove the steering wheel and all?

I'll go do some more checking and let you know the results.

Greg

#12 Cougar

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Posted 14 July 2004 - 08:53 PM

Here is what my manual shows for the wiring to the ignition relay.

The red fusible link ties to fuse #5 which feeds a wire that changes color to black/white, going to the relay. The other side of the contact goes too two white wires.

One of the green fusible links ties to another contact in the relay and it changes to a red wire going to the relay. The other side of the contact goes to a red/blue wire.

There is another critical wire coming from the ignition switch. It ties to fuse #20 and goes to the ECU via a light green/yellow wire-pin #18 at the ECU. BE SURE THERE IS 12 VOLTS AT THE FUSE AND AT ECU PIN 18 WHILE CRANKING THE ENGINE!




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