Need some wiring/no start help

[Fastmax32168]

I am trying to get the 3500 I swapped into my Monza to fire and not having much luck.
I think it may be a fuel pump wiring issue but I am not sure. This is an OBD1 conversion.
When I turn on the key the fuel pump runs and primes.
When I crank the motor over the fuel pump does not run and I get no spark.
I have no spark when cranking until the moment I stop cranking, then I get one spark.
My scan tool tells me the ECM is seeing no voltage to the fuel pump, not even when the pump is priming, however the hot gray wire that feeds the fuel pump is also running to the ECM. Perhaps I am wrong about that being the sensing wire?
Would the ECM seeing no voltage to the fuel pump cause a no spark condition?
Thanks
Roy

[TGP37]

Seems like the crank sensor might be failing or the wiring is bad/backwards. I haven't messed with 3500's

I would get a multimeter and start testing. Check to make sure you are getting proper voltage to the ICM, make sure the grounds are good.

The starter draws a lot of amps. Noting you do not get a spark until you stop cranking might indicate an issue along those lines. Make sure the block/frame is well grounded to the battery.

[Fastmax32168]

Crank sensor is new and shows good AC signal when cranking. All the coils test good. I have power to the module and a good ground leaving it as well. I am going to test the voltage to the module while cranking later tonight to make sure it is not falling way down under load. I am suspecting the ignition module may be no good but have been unable to really find a method of testing it other than making sure it has power and signal. I may have to take it into the local parts stealer to have it tested.
Roy

[TGP37]

Testing the ICM is a good idea. Be sure the crank sensor is wired properly. I happened to wire the polarity backwards and it was a nightmare trying to diagnos.

[Fastmax32168]

I could try switching those wires. I did not have the original sensor plug when I wired it so I had no way to know which way was right. I really didnt think it mattered.
Thanks
Roy

[TGP37]

I could try switching those wires. I did not have the original sensor plug when I wired it so I had no way to know which way was right. I really didnt think it mattered.
Thanks
Roy

Oh it matters alright....lol

I had used a pigtail that appeared correct, but was backwards. Took me 3 months and a few hundred bucks before I happened to find the original pigtail and the light bulb went off.

Same thing happened. I had zero spark until I let off the starter and then it just stumbled for a sec or two and died.


The sensor has a high and low circuit. If they are switched, the low becomes high and high becomes low. The 6 notches plus the 7th for TDC become misread and the coils will not charge properly.


Now, I am an OBD2 system. I don't know for sure about OBD1 but I believe the crank notches are the same so the sensor action should be the same.

[Fastmax32168]

I had used a pigtail that appeared correct, but was backwards. Took me 3 months and a few hundred bucks before I happened to find the original pigtail and the light bulb went off.

Take solace in the knowledge that your tribulation was not in vain grasshopper. It looks like the exact same thing happened to me. As soon as I switched them I had spark. Thank you very very much.
It still wouldnt start, it had that timing is all screwed up sound. After some more research I figured out that when you stick a front drive motor in a rear drive car 135 end up on the passenger side and 246 on the drivers side. A bit of switching around of plug wires and bam. Fired right up!
Thanks again
Roy

[TGP37]

That is fantastic Roy!!!

I am glad I was able to help.