LS no start = help please

[lutronjim]

I have a LC9 (ls3) with 65E tranny in my 70 C10 (connect and cruise package).

I have a no start condition (cranks but will not run) with no codes nor cel.

On key on I can hear fuel pump run briefly which is normal. This tells me computer has power and it sees enough fuel pressure to turn off pump.
I have a tank in back, in tank pump, pressure regulator near tank, filter near tank, and fuel line to engine - all new at conversion 3+ years ago.

Turning key to start cranks the engine but no start.

I'm guessing its either missing spark by not firing coils or missing fuel by not firing injectors.

This has happened 3 times in the last 3 years usually on first thing in the morning. By wiggling connectors and trying again got it going to get home. Don't have a clue if wiggling did anything or it just decided to start.

But if it will start, how do you find trouble. Complaints to GM got them to replace the entire wiring harness on their dime during year 1.

This morning I drove it to church for a meeting and 75 minutes later - no start.

Got wrecker to bring it home. This thing has been running great for the last couple of years sans my problem with the brake booster.

Wouldn't start at home. I swapped fuel pump relay with ignition relay - no start. Swapped fuel pump relay with power relay (I assume this is for computer) - no start. Fuel pump relay is good because I can hear it run

I was thinking of putting meter on coils and injectors to see if they are getting firing voltage. Problem is I don't know colors and don't know if my Fluke dvom will show up a short pulse.

Truck is on street and I will try in morning to see if it will start.

Any help would greatly be appreciated.

[mongocanfly]

when it wont crank ,have you checked to see if its firing?...also can you check fuel pressure at the rails?

[First c10]

Things I would check:
Is there 12+ power to the ECM/TCM while cranking.
This could be the actual ignition switch.
Are the coils firing? Check spark at spark plug wire.
Check fuel pressure at the fuel rails like mangoanfly indicated.
Not sure how they connect and cruise all works as far as the VATS?

[lutronjim]

FirstC10

Is there 12+ power to the ECM/TCM while cranking.
This could be the actual ignition switch.

This sounds interesting - any idea of how to check? I don't have any idea of harness wires?
Do you know what color wire comes of of switch?
I would tend to think fuel pressure would be OK since it runs fine when it starts.

How can I check spark without frying something?
Thanks for comebacks.

[mongocanfly]

the only thing the ignition switch does is crank over the engine,and supply switch on power..
you could use a old spark plug to check spark..dad used a screwdriver to check..it would take 2 people to do this

[First c10]

Originally Posted by lutronjim

FirstC10

Is there 12+ power to the ECM/TCM while cranking.
This could be the actual ignition switch.

This sounds interesting - any idea of how to check? I don't have any idea of harness wires?
Do you know what color wire comes of of switch?
I would tend to think fuel pressure would be OK since it runs fine when it starts.

How can I check spark without frying something?
Thanks for comebacks.

My first swap I had a problem at the beginning as it had the original switch or at least an old one. When you were actually cranking the engine over it had intermittent 12+ power to the ECM so it would not start. I think it’s a large pink wire from the switch.
I was just thinking as it has been running so it’s got to be something that can ware out or break. Etc...

Pull the plug wire, stick a screwdriver in it and let it rest next to the block/header or something it can ground to. Turn it over and have someone either turn it over or check for spark. If no spark need to check powers or grounds.

[homemade87]

Jim , To answer your question on wires to check . If you get no spark at the plugs take your volt meter and check the pink wire at the coils on both sides . You can do this at the main connector that plugs into the coil packs . You should have 12v all the time when key on . If no 12v go back to your fuses and look it over and check for 12v in and out for the coils .

After checking and if this is a problem let us know what you come up with .

Also to comment on your first post on fuel pressure . The ecm does not know what the fuel pressure is . When you key on the pump it will time out after 3 seconds from the ecm . It is not measured buy fuel pressure . So checking fuel pressure would be a good idea just to rule it out .

Being a intermittent problem you have an advantage right now that it is in a failed state . Dont move things around to much until you get to check the voltage out . It may fix itself and be chasing your tail .

[lutronjim]

Now I tried to start truck at least 5 times before calling wrecker. It bounced all the way home and left on the street. I tried to start again with no luck.

Had to work on lights at church so late in the evening I went to look at truck with the idea of trying to hot wire computer and then try to start - bypassing switch if you will.

Well I opened door - put in key and let fuel pump run - kit start - I bet the starter didn't turn 3 teeth before the damn thing bust into fast idle. Didn't even get into truck.

I hate to throw parts at a problem but the switch, as suggested, seems to be a fair bet.

Now I'm going to have drill lock. Key will come out in 'on position' and will
not turn into accessory.

[First c10]

I hope that is all it was. Sorry to hear about having to drill out the lock. That sucks as your ignition key wont match you door locks unless you change them all. That's more work then the ignition switch problem. keep us updated!

[Sledgebone]

See if you can have someone with a scanner check to make sure the crank position sensor is reading. I had this same issue on my DD. Failed to start, towed home fired right up. Mine actually died while driving on the expressway with no codes. Only way I caught it was with a Bluetooth obd scanner from my phone. It was a pending fault and as soon as it started again it cleared.

[lutronjim]

Went to Summit yesterday and got ACDelco cylinder but had to get a Standard switch.

Drilled lock cylinder today. Since it would not turn to left, I had to drill deep to cut 'pegs'.
When I pulled out switch it blew open. The contact 'plate' had 1 contact that was 50% burned. I took a picture and if my phone will ever upload it to google photos, I'll post it.

Put it back together and it cranked. One difference is that I noticed that the break light comes on in the crank position - it didn't before. Don't quite understand how that works - I thought the proportion value grounds to make light come on.

[rennat_2006]

If it happens to act up again on you give it a shot of brake cleaner, carb cleaner, or bill cosby in a can(ether) and see if it lights off. Quick easy way to check for lack of fuel or lack of spark.

[First c10]

Ok so after the new switch did it start up and run normal again?

The dash “brake” light is what you are talking about correct?

[paul mora]

One of the post pointed out have a can of started fluid spray. This has always been my test tool for a non starting car. A quick spray in the intake and if it fires its fuel problem if it cranks its a voltage problem. This give you a good idea where to start looking before you throw parts at the car.

[lutronjim]

Bad choice of words 'cranked' on my last post. It started and ran fine.

Here is picture of some of the switch contacts. The bar piece shows how its been arking. Since it blew apart on removal, I don't know what it or contacts 'switch'.

I like the starter fluid idea. Would it harm the mass air flow sensor if I put into intake filter?

[First c10]

Glad the switch was the issue. Easy fix!