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Ron
Ron, ASE Certified Technician
Category: Mazda
Satisfied Customers: 33468
Experience:  35 years as a automotive tech
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30 year ford mechanic and this old mazda b2600i is kickin my

Customer Question

Hi George,
30 year ford mechanic and this old mazda b2600i is kickin my ass
Submitted: 1 year ago.
Category: Mazda
Customer: replied 1 year ago.
First off, a little history: 91 mazda b2600i almost 300 k on it, car will start cold, then after 12-15 mins of driving, dies, cranks wont start and you can smell fuel. so I checked for spark, no spark. after initial visual inspection, I decided to try a distributor because of general nasty appearance. installed new distributor and ign module, (on L fender) started truck, drove for 15 miles, ran great and then just shut off, cranks no start, thought since the dist. and module were new and symptom is the same as before, went to wrecking yard and got a used coil, tried still no start. started reading online and testing. tried to check relay but not sure if I was successful. ok here's where it gets weird, again reading online- found out the computer could be screwed, pulled out opened case, NO corrosion inside looks brand new, no smells, no moisture, etc. read theat the computer controls the injectors as well as the coil, ANYWAY, if I disconnect the large harness at the intake throttle body area with the ket on, I get huge blue spark from the coil wire to ground.. HELP ME HELP ME
Expert:  Ron replied 1 year ago.

Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

With everything you have replaced I would start with checking the harness from the ECM to the distributor. I have enclosed some test steps to check this. Copy and paste the link below to open and view it.

https://dl.dropboxusercontent.com/u/104923897/ECM%20test%20Oct%2013.pdf

Customer: replied 1 year ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 1 year ago.
Ok Ron, here's my problem, the truck starts and run great cold, then after 15 mins of driving it dies, just shuts off, no stutter at all,then test for spark, no spark at all. so, distributor, igniter,cap and rotor all new. used coil from another truck. Last night while checking things out, I noticed with the key on, if I disconnect the injector harness plug at the front of the intake, I get a huge blue spark from the coil wire to ground. does that help?
Customer: replied 1 year ago.
do I have to get it hot enough to die again, then run all tests?
Expert:  Ron replied 1 year ago.

Run the steps I sent you and let me know the results and we can work from there.

Customer: replied 1 year ago.
Ok Ron, ran the tests, here are the results: The Igniter has a ground
I do not have an osciliscope so I cannot check for a square sign wave while cranking on the red/yellow wire but with my multi-meter I get a voltage bouncing back and forth between 2.9 and 3.8 volts
again, no scope so I went to step 4 and at the distributor on the pink wire and the yellow/ Blue wires I do have a 3.092 reference voltage
Expert:  Ron replied 1 year ago.

Are you sure the new distributor is not defective?

Customer: replied 1 year ago.
It has the same symptoms as before the new distributor,, however, do you have a quick test to verify the distributor?
Expert:  Ron replied 1 year ago.

Yes but you will still need a scope to check it. See it below.

https://dl.dropboxusercontent.com/u/104923897/Dist%20test%20Oct%2013.pdf

Customer: replied 1 year ago.
Okay, again no scope but I have fluctuating voltage according to the tests you sent.
That seems ok, the bottom of that stated to check power and grounds at ECM, so I did and on the 2K connector cavity, I am supposed to see a Vref of 4.5 to 5.5v what I am seeing is more like 2/3rds of a volt.
The Vref appears to be an output from the ecm so would that condemn the ECM?
Customer: replied 1 year ago.
I did find a burned spot inside the ECM, there are 2 resistors side by side that are on the 2K circuit and that's where the burn is. I guess Ill have to get an ecm for it
Expert:  Ron replied 1 year ago.

Yes VREF voltage come from the PCM and this does sound like a failed PCM especially if you found a burned spot.

Customer: replied 1 year ago.
I have a used Pcm coming tomorrow. I will let you know how it turns out.
I started the truck this am and let it run for 15-20 mins, then watched it with a volt meter, the Vref went from a very steady 5 volts down to .2 volts and the truck died. So as an additional test I removed the pcm and put it in my freezer for 20 minutes. The truck started up with the Pcm cold
I think the replacement p c m should fix it
Expert:  Ron replied 1 year ago.

It sure sounds like you have it. Im here all day so post back if need be and we can work from there.

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