91 explorer starting problem, spark related

[merc2dogs]

Hello all, new here, been searching the net for the last couple days to looking to fix this problem, been dealing with it for a few weeks now, and haven't made any headway on it

The problem is that it takes a lot of cranking to get it started, once it starts, it runs fine, extremely well even. I drive anywhere from 80 to 150 miles a day for work (round trip Holland/lansing etc, I'm in construction), and while it's running there's nothing at all to complain about, and great mileage

also, when I first had the trouble I pulled codes, and all I got were a bunch of old codes,and one 'new' tps code, cleared codes, replaced tps, drove it for a while, pulled codes again, and nothing came up as wrong

the main symptom is that I get 2 or 3 nice sparks when first turning the key,then no sparks, with an occasional yellowish, sputtery spark every now and then.

it will start with long cranking, but I have a better chance with short kicks, I've burned out too many starters in the last week and a half from the cranking, (lifetime warrenty thankfully!)

I swapped out the ignition module (had one from a known runner), then had that one checked as it didn't solve the problem,
borrowed an ecm, and that had no effect,other than one 'normal' startup, so I swapped back to my old one.

everything I checked out came out good, the only problems I can find is that on the wires to the crank sensor, I have 1.5v on both leads (to ground), instead of on 'one' wire as stated in the haynes manual.
and that I am getting the same 'signal' at the coil low side as I get from the spark test (couple sparks, then a few every now and then)

as far as the crank sensor, I've been given differing specs, most claim that I should have some resistance accross the lugs, others say only that I should have a voltage pulse when cranking the motor. I have 0ohm resistance, but get voltage pulses of roughly 500mv, which makes me think that's ok

did try running a hot wire to the coil instead of the ignition wire on the off chance that I had a low voltage feed, with no change either

frankly, I've checked everything I can think of, and can't find anything wrong except for the voltage on both leads for the ckp.

any help is greatly apreciated, it's getting way too cold to take the bike to work anymore!

thanks
merc.

 

[merc2dogs]

possibly fixed

don't know if it actually fixed it, but it reduced the cranking a lot, two or thre seconds max last four starts anyway.

put the crank position sensor on a variable power supply for a couple seconds at 1.5v dc, then ran through all the same tests again, and came up with an open circuit through the connector, my guess is that the sensor heated up enough under normal starting conditions to open the break, makeing the system read it as not being there.

merc.

 

[TPLYNCH]

Glad to hear you may have found the problem! Another trick you may want to try is cycle the fuel pump 2 or three times (on/off, on/off, on/off waiting for the Fuel Pump to stop whining before turning to off) before going all the way to start. At that age, especially with an original pump, the check valve may be bad and letting gas drain back to the tank. Try it and see if it turns over sooner.

 

[merc2dogs]

Glad to hear you may have found the problem! Another trick you may want to try is cycle the fuel pump 2 or three times (on/off, on/off, on/off waiting for the Fuel Pump to stop whining before turning to off) before going all the way to start. At that age, especially with an original pump, the check valve may be bad and letting gas drain back to the tank. Try it and see if it turns over sooner.

tried that, was realy hoping that was the trouble, as I had a new fuel pump in the garage for it, checked it though, the pressure was 40psi with the key on, 30 psi when cranking, and held 30 running, also would hold 40 for as long as I left the gauge on it.

so far the crank sensor seems to have done the job, haven't had any surprises.

thanks.

merc.