Crank no start no fuel pump prime

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Home / LT1-LT4 Modifications
97 f body ICM testing
#1

951LT1 , Today 07:30 PM
Teching In
Cranks No start and no key on fuel pump prime.
ICM connector 12 vdc A and D 0 vac B cranking Continuity B to PCM good 0 ohms.
PCM Red A7 Drk grn/wh Fuel pump relay 0 vdc or vac when key on at all (not 1-2 sec) fuse is good
PCM Power 12 vdc also PCM tuner tested good.
​​​​Grouunds cleaned.
New Petris Opti and Coil Known to be good ICM.

Thoughts??



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Connecting... Need help on lt1-ls1 electric

#1

merim123 , 05-05-2012 11:23 PM
TECH Fanatic
I'm getting ready to say I need to try another PCM

Here's what I have done:

1) all pinks + orange have power and traced back to pcm connectors 1x1 to make sure power is getting to the PCM = OK
2) continuity check from pcm to OBD2 port = OK
3) continuity check on fuel pump to relay is = OK, getting 12 volts on green/white wire at relay
4) all grounds tested for continuity at pcm and on body =OK
5) all connections nice and tight on battery and distribution block =OK

I can crank just fine no issue. I cannot connect to the PCM, just getting a 'connecting...' on my scanner, so I can't tell what is wrong.

Also- fuel pump will not prime by itself via PCM, VATS is disabled in the tune, but I'm thinking it's a relay for now, because when I give power to the grey wire, I can hear the fuel pump working. at the fuel pump relay, key on, I have a good ground, and have power at the pink and PCM wires.

I don't know how I would have bricked my PCM, but thought I would try here and see if I'm missing anything obvious in my configuration or something I may have overlooked.

Thoughts?

#2

LS1MCSS , 05-06-2012 07:34 AM
TECH Junkie
Make sure you have the fuel pump relay wired correctly. Do you have battery power to the OBD2 port, not switched power?

#3

merim123 , 05-06-2012 03:33 PM
TECH Fanatic
Fuel pump relay wiring is factory on these cars, I just need to bring the relay green/white to provide PCM power which I did. Obd2 is wired correctly with the two grounds and PCM
Feed traced for continuity.

I think I have to try another PCM at this point, not sure what's left

#4

Rick Speed , 05-06-2012 07:12 PM
TECH Resident
Make sure you have the correct wire for the obd2 because the PCM actually has 2 and one won't work with the scanner. What year PCM? Make sure the fuse is good inside the car

#5

merim123 , 05-06-2012 09:59 PM
TECH Fanatic
I had another mtor in this car with this pcm, it all worked fine. I think I'm either fighting a bad now pcm or something in the ls1 harness which is the only new variable here.

#6

Rick Speed , 05-06-2012 10:40 PM
TECH Resident
Make sure the grounds on the back of the head all got bolted up

#7

merim123 , 05-06-2012 11:42 PM
TECH Fanatic
Yup, i did at with the engine out of the car when i plugged the harness in first. I bolted all of them to he back of the head on the drivers side. Also my ground strap is going from drivers side cyl head to frame.

Tried the pcm in another ls1 car, fired right up, and died a few seconds later, assuming thats because of my much bigger injectors in the tune vs stock ls1 injectors. I was able to scan and read the tune off my pcm in the other car.

Also, made a new obd2 connector directly off the pcm and still cannot connect. Hate these gremlins!

Checked voltage at coils and fuel injectors and good there.

#8

the_merv , 05-07-2012 12:40 AM
11 Second Club
What spot in the PCM connectors is the Pin 2 on the OBD2 Connector goin? 4&5 grounded? 16 constant 12v?

#9

merim123 , 05-07-2012 01:23 AM
TECH Fanatic
Pin 2 goes to blue58, 4/5 grounded to battery distribution ground, 16 running off of battery power distribution block. Tried to take out all the variables.

#10

the_merv , 05-07-2012 02:13 AM
11 Second Club
That's correct.. Have you tried testing the wires with a multimeter?

#11

merim123 , 05-07-2012 09:19 AM
TECH Fanatic
I tested all the wires right at the PCM connector. so I have grounds on 1 and 40 on red and blue connectors, i have good continuity on them back to the chassis ground bolt by the battery. my resistance on the ground cables for the battery grounds and block grounds are all less than 1 ohm so don't think it's the cables.

For power, confirmed my constant power is there at blue 20 and 57, then with key on, I have power at blue 19.

I have the basic for it to fire wired, which is frustrating. I also ran a new wire from the pcm directly to the fuel pump relay just to make sure I don't have any short in the harness.

so with all the grounds good, and the pcm power good, i should at least be able to connect and read it with my obd2 connector directly coming off the pcm now with my rewire.

ugg when i did my 24x conversion, this fired up right away with this pcm and I repinned my entire lt1 harness from scratch.

now actually using a ls1 harness I can't get it to fire

#12

the_merv , 05-07-2012 02:14 PM
11 Second Club
Have you checked the continuity on 58?

You said you had a LS engine in this car before and it ran?

#13

merim123 , 05-07-2012 02:37 PM
TECH Fanatic
i just ran a new wire to pin 58 that's about 18" long, I have the obd2 now by the pcm to eliminate anything in the wiring harness.

I had a lt1 engine in here running 24x with this pcm. so the only new variable here is the ls1 harness and the ls1 engine. everything else is the same as it was in the car previously.

#14

merim123 , 05-07-2012 08:10 PM
TECH Fanatic
and it RUNS! Thanks to G-Body for stopping by to help me out!!! Turned out to be my constant power was failing under load and pcm wasn't getting enough power to turn on. I used what I thought was a good constant, but once we checked it under load, we realized it was not ( it was the air pump relay constant for those searching and don't tap that for constant power for the PCM) Once we reran the constant power it fired right up.

#15

the_merv , 05-08-2012 03:48 AM
11 Second Club
Ah good. Constant PCM power should have its own fuse..

#16

merim123 , 05-08-2012 02:39 PM
TECH Fanatic
Quote:
Originally Posted by the_merv
Ah good. Constant PCM power should have its own fuse..
Completely agree and I thought I had it through the factory harness. I was trying to use as much factory wiring as possible myself, and just got greedy too quickly with this circuit. Now I have a 10amp fuse going directly to the battery power distribution box

Now I can finish off the rest of the wiring and get my alternator signal and all the other gauges working. Your thread on that is helping big Merv, thanks!

#17

the_merv , 05-08-2012 03:41 PM
11 Second Club
No prob man..that's what it's there for..

#18

LSCha0s , 05-08-2012 05:09 PM
TECH Enthusiast
Man! I'm done with everything but the wirring at this point.. Threads like this scare me. I'm glad to hear you got it worked out.

#19

merim123 , 05-08-2012 05:36 PM
TECH Fanatic
Quote:
Originally Posted by LSCha0s
Man! I'm done with everything but the wirring at this point.. Threads like this scare me. I'm glad to hear you got it worked out.
when it goes well, it's the easiest thing, when it doesn't it just takes longer, but don't let it scare you. It is really simple and easy, one line at a time and don't overlook any of the details (e.g. like my obvious overlooking of just assuming my constant power was good enough that I had in the harness. Trace it back and test it to make sure you really have good constant power that doesn't drop voltage under load like mine did).

#20

LSCha0s , 05-08-2012 08:25 PM
TECH Enthusiast
Thanks .. to be honest this site and Pocket have helped a lot and gave me the confidence to make my own harness.

Tags
chassis, connecting, connections, constant, engine, fuse, harness, ls, ls1, lt1, pcm, power, pump, relay, start

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Update: Ran 12v switched to B3/C30 Restored FP prime and ICM/Coil/Opti connector voltages are correct. BUT NO Spark coil out or sparkplugs. Have Injector pulse. 
T21 14 pin connections as found by PO Pin3 A7 Pin4 to 2 pin sensor located under fpr. Pin5 ground Pin6 oil press Pin8/10 coolant temp. I'm aware not correct. Should have 12v switched from T21 correct?
Still using DME relay for FP. 
PCM vats delete / no codes scanned.

EXTENSIVE input SHBOX.
HELP ANYONE?