I have a '91 B2600i 4x4 with a newly re-surfaced cylinder head which I removed and replaced, a new thermostat, a new oil pressure switch, new plug wires, new distributor cap and rotor, new NGK plugs, and a clean bill of health from local Mazda dealer's shop (quack, quack). It's been missing intermittently for awhile, and that is one of the reasons I took it to my local Mazda duck. They removed my Bosch platinum spark plugs and replaced them with NGK plugs, charged me $70, and declared the problem was solved. The miss has goten worse since they "fixed" it, and I tested the injectors first by swapping #1 and #2, (the #2 position still wouldn't fire), and then pulled the injectors and fuel rail away from the intake to observe firing, and found that only #1 and #3 were firing. I swapped 1 and 2 again, no change. Still firing #1 and #3. So I don't think my injectors are to blame, but what is? All connections are clean and tight, and wiggling wires doesn't change anything, so it doesn't seem to be a loose connection either. I'm at wits end at this point, so please give me anything you've got. Thanks.

 

looking at the wiring diagram
check for power at the injector key on
have someone crank it over and check to see if the ground is getting the trigger from the ecm
maybe a bad conection for 2 & 4 at the ecm or injector harness (check this first)


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I have verified the positive 12 volts, but the negative firing pulse is so fast I can't detect it on the 2,4 or the 1,3 wires with my digital meter. It makes sense to me that the negative pulse is the problem, but how do I find the break in the signal if I can't check signal? Where does the pulse come from, and how do I measure it?

 

easy use a test light or if you can get one use a fuel injection "NOID LIGHT"
you only need to see if the ecm is grounding the injectors
light will flash with pulse's

 

OK, so I need to check the LG/B and the LG/R against the B/Y to see if the computer is sending the ground, right? I don't know about a noid, but a test light is easy enough to find. If there is no ground signal, where is the next check?

 

if the connection on the fuel injection harness is good. then with an ohm meter test the ground wire from the injector to the ecm light green with a red trace line. if the wire is good showing 0 ohms then the ecm has a bad internal connection and should be replaced

 

Yup, It's the computer. The wires test good from the computer connector to the injector harness connector, and the ground is not coming through. Where is the best place to go for the computer, Av-Pro ECM? Does anyone have experience with them or anyone else, good or bad?

 

the prev owner replaced the one in the truck with a standard motor corp #em736
with the old cab i guess it leaked cause he had it in a plastic bag sealing it
i work with this guy and the ecm is in to the 3rd year now(and a new cab no leaks no bag)

 

I haven't been able to find a standard motor corp #em736 online. Do you know where he got it and how much it was?

 

local parts store in town here had to order it. not sure how much it was though