89 no start

I have been battling a no start issue here we go.

last owner installed in an attempt to get it to start.

new crank sensor
new cam sensor
rebuilt starter

I have power going into the pcm at pins b7 and b8 key on
I have good ground at pins b11 b12
I have source voltage to the tps from the transmission computer to the square connector
All the sensors have good ground

I do not have source voltage out of pins c14 to the map or c15 to the tps
I have not figured out how to test if I have tach input to the computer yet?
But I am more worried about the lack of source voltage to the tps and map being my problem.

Am I on the right track to buy a pcm?

I took this one apart and it looks and smells fine. I have a want to buy or barrow post up in my local chapter now for a known good test unit.

So I guess i'll see what happens! Any help will much apreshiated (sp?)

Dave

I'm assuming it turns over / won't start.

99Redxjbuilder said:

I do not have source voltage out of pins c14 to the map or c15 to the tps

Click to expand...

Is that with the key on?


How about 12v at B10 with the key on? You can check for this voltage on Diagnostic connector 2 pin 5.

If that is missing, check your latch relay and/or ignition switch.


Having a test computer to swap in there would be a quick and easy way to either target or eliminate the computer. Maybe with some luck you will be able to borrow one.

I'd be curious as to what caused the 5 volt signal supply to fail. Or if there isn't a short someplace sucking the voltage down. Just guessing but it seems unlikely the 5 volt signal to the sync sensor, the O2 sensor, the MAT, the TPS and the engine temp. sensor (lower left block) are divorced from each other. The likely share a common source.
If the 5 volt power supply is failed, the first question is why, there may be a short or failed senor that cuased the supply voltage driver to fail or a dead short someplace else in the system causing the output at the MAP and TPS ECU pins to read zero.
Maybe unplug all the sensors and see if the 5 volt supply doesn't come back (ECU). Maybe test all the sensor circuits with the sensors unpluged and the ECU unplugged with an ohm meter and test the circuits for shorts. Do an ohm test on most all of the sensors and test for "0" resistance. Though the syn sensor is a pulse and may have no resistance to begin with.
Maybe test some of the other sensors for the 5 volt supply, like the sync sensor.
I've heard of, some way, 12 volts (battery voltage) finding it's way into the 5 volt supply circuits with catastrophic results. Though I've never seen it, myself.
It would be a real bummer if you plugged in your new ECU and it failed (smoked).

The Renix fuel injection manual, may be a better source for testing than the FSM.

MapleDitch said:

I'm assuming it turns over / won't start.




Is that with the key on?


How about 12v at B10 with the key on? You can check for this voltage on Diagnostic connector 2 pin 5.

If that is missing, check your latch relay and/or ignition switch.


Having a test computer to swap in there would be a quick and easy way to either target or eliminate the computer. Maybe with some luck you will be able to borrow one.

Click to expand...

Key on turns over no start.

MapleDitch said:

I'm assuming it turns over / won't start.




Is that with the key on?


How about 12v at B10 with the key on? You can check for this voltage on Diagnostic connector 2 pin 5.

If that is missing, check your latch relay and/or ignition switch.


Having a test computer to swap in there would be a quick and easy way to either target or eliminate the computer. Maybe with some luck you will be able to borrow one.

Click to expand...

Thanks!!! it now runs. The latch relay is not getting power from the ignition but thats ok at least I know what the problem is.

If you got it running by jumping power to the latch relay, then I suggest you check the fusable link for the latch relay (it's one of the many wires that come off the starter relay next to the battery).

Glad to hear of some progress:thumbup:

MapleDitch said:

If you got it running by jumping power to the latch relay, then I suggest you check the fusable link for the latch relay (it's one of the many wires that come off the starter relay next to the battery).

Glad to hear of some progress:thumbup:

Click to expand...

Nope cut out all the links! It's somewhere from the relay to the trigger point ignition switch maybe? (It's a pink wire) But I think it's going to get sold as is or maybe run a wire from another hot when keys on wire to it just to sell it

ok pink is on connections 4 and 5 of the relay this can be measured at Diagnostic Connector D2-5 and of course B10. Position 2 is the latch relay GND (BLK-T) going to Diagnostic Connector D2-3 and to the ECU on A9. Connection 1 on the relay is from the B+ and should have an Orange fuseable link. You should either reinstall fusable link or inline fuses where the fusable link was before you sell it. It is a safety issue not having them in there. I have had one computer go out on me and bought another rig with a broken ECU. The thing that they had in common was the the grounds went out. I watched the grounds go out on my 88 and kept bypassing them till I was like this is F'd. The 87 had so many wires added it was easier for me to remove them all and start from scratch and it was both the ECU and the CPS that had gone out on that one. Good luck and remember safety once it works.