96 D1 starts occasionally

[Tom in MD]

96 D1 starts occasionally - UPDATE

I recently had a crank-but-no-start condition. No fuel at the rail. Fuel pump fuse was blowing immediately upon attempted start. By-passed the harness to the fuel pump with a 15a fused wire and pump ran fine. Replaced the little harness out back and she ran fine. Week later, crank-but-no-start and I observed:

• fuel pressure at the rail @~38p
• Check Engine light was not lit when key in pos 2
• no flashing LED for alarm
• door locks don't lock centrally with the key fob nor by the drivers door

Seems that so long as there's no Check Engine light in ignition key position 2, the truck is a no-go even though fuel pump runs and pressure is good at the rail. If the light is on, she fires up. Problem is, light only comes on in seemingly random situations. If I disconnect the battery, then re-connect it, the Check Engine light will light in position 2 and the truck fires up.

:smilelol: So I've got a 3000 pound slot machine in my driveway, and I'm not feeling very lucky right now. I guess I'll be travelling with a 13mm spanner to disconnect the neg battery terminal for now, but any ideas what's at the root of this evil?

My thought is that the immobilizer has somehow gotten jacked. Possibly due to low voltage condtions during my last "fix" because I ran the battery down. The battery is holding more than 12v now. For full disclosure, I thought I'd mention that the fuel pump is about 50K miles old.

Tonight I will leave the negative battery terminal disconnected and pray to the Disco Gods to see if the Immobilizer Faeries visit me. I don't know what else to try.

I'd appreciate any ideas or sharing of experience. I've read lots of info about no-start issues on this site, but I'm not finding any help in the archives.

Thanks!

 

[ptschram]

Lemme get this right. The truck will only start if you disconnect the battery and reconnect it?

OK, you got me! I've never heard of, nor encountered this one.

On older GEMS trucks, the first place to start is disconnecting the ECU and cleaning the connectors on the harness and the ECU, then do the same to relay on the fenderwell directly forward of the ECU.

Good luck, keep us updated as this is a curious one.

 

[p m]

Tom - I've posted this before, but I am not sure if this is a common thing.

I had exactly your symptoms, to the tee, on a 96 D1.
It turned out to be the following:
- a sticking door lock was causing the alarm box to blow not one, but two fuses. I've replaced both, and everything went to normal. Then it blew one of these fuses again (the larger-rated one, that feeds the transistors that control the door locks). I replaced it with a 25A current breaker, and it's been good since 2002.

The dealer wanted to replace the ECU, at (then) the cost of $2200, after spending four days on dumbass diagnostics.

 

[Tom in MD]

Thanks for the replies, guys! You guys got me moving again....atriot:

PT: Yes. I know it's weird, but when I initially try to start the truck, all the normal lights but the Check Engine light illuminate in the dash cluster at key pos 2. It will crank strong, I hear the pump come on for it's ~5sec run, and has fuel pressure at the rail of ~35-38p. If I disconnect the neg battery terminal, and reconnect it, turn the key to pos 2, and there's the Check Engine light shining. Starts right up.


PM: Because my key fob stop actutating the door locks, it got me thinking something was wrong there. At this point, even trying to centrally lock with the key does not work.

When I read your post it dawned on me that there are other fuses involved that I hadn't checked. I was looking at the "Central Door Locking" fuse in Satelite 2, pos 4. You're reply compelled me to inspect the "Anti-theft alarm" fuse in Satelite 1, pos 1, and it was BLOWN!:applause: Popped in a new 15a fuse and now the door locks actuate better than ever, the Check Engine light comes on with the other lights as it should, and the truck fires up 10 out of 10 times.

Jackpot ? Well, with this truck, you never know, but I'll take this as a temporary victory on behalf of DWeb.

Thanks so much guys. This was a weird one for sure, but I guess I need to inspect the door locks to make sure they're not sticking. They've been very slow to actuate for years, and it never occured that it could be wearing down the circuit.

 

[p m]

:victory:

 

[ptschram]

Peter:
My first check is fuses! There is an admonition from Gary written on the inside of the door of the fluid room telling me to check relays 1st. Beneath it, it says FUSES!

 

[p m]

There's a ton of them, and I don't know where half of them are.
So I ended up printing five pages of Electrical Troubleshooting Manual related to electrical diagram around the alarm box, and figured it out.

Drove me nuts, though. My wife has been driving for a month with a 13-mm wrench in the map pocket on the driver's door.

 

[Tom in MD]

Ya, PT. It's always the simple things. I thought I was smarter by checking what I thought were the associated fuses, but wrong. From now on, I'm looking at every fuse before I touch anything else.