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No spark?

Wrench

Wrench

1/2 ton status
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Jul 19, 2007
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Location
Stony Plain, Alberta
Never been much of a TBI guy, but I've been driving the V3500 and it's been great until recently it started occasionally dying when idling. It's only been a couple times, and always started again after a few long cranks, but this morning I started it, came in to grab a couple things, went back out and it was dead. Now I can't start it at all :mad:. I put my inductive timing light on a few of the plug wires and it's showing nothing for spark when I crank the engine. My tach needle still bounces around when cranking though, so there must be power at the dist.?

I'll keep checking on things, but any ideas would be welcome . . .
 
Ignition module, pickup coil, coil wire if separate coil, wiring from distributor to ECM.

I'm not sure if the crank no run chart in my troubleshooting thread is large enough to read how to test that stuff.
 
Where is your troubleshooting thread?

Doesn't look like the injectors are squirting either. I'm poring over wiring diagrams in my Chiltons and Haynes manuals :doah:
 
the module(sp) controls the spark and fuel. they are know to go bad. in the past 2 weeks i changed 5-6 of them.
 
The truck is equipped with a MSD 6A ignition module, MSD coil, and MSD distributor. What looks like the factory terminal has two connectors that hook together and look like they would plug directly into the coil, but they are plugged into the harness that goes to the MSD ign. module, and then one plug comes back and plugs into the coil.

One of the factory connectors has a 12ga pink wire and a 14ga white wire into it, the other connector has a 14ga pink and a 14 ga white wire in it. The 12ga pink wire has power with the key in run, none of the other pink or white wires do.
 
By bypassing the MSD, you mean plug the factory connector directly into the coil?

Does the MSD ignition module not actually replace anything in the system?

Edit: that troubleshooting flowchart is da shizzle . . .
 
I think the MSD actually just plugs into the system. If the stock connectors fit, it's fine. All are keyed AFAIK.
 
Ok, tried that, same symptoms except now my tach doesn't work. I found it interesting that the way the connectors fit together, the 12v pink wire goes into the terminal side that was unused on the coil when the MSD was hooked up. Not making sense to me--have to follow all the wiring in the morning. I did find instructions for installing the MSD box online . . .
 
Are the 454 and 350 TBI ECM's the same other than the chip? for example, could I swap in an '89 ECM from a 350 and move the chip over to verify that the ECM is not the issue, or would I need one from a 454?
 
I just recall some folks talking about MSD and not needing to do anything to "bypass" it except to re-join the factory connectors. May depend on the application, their instructions should be pretty clear.
 
The MSD box can either be installed using a plug and play harness (no cutting and splicing factory wiring) or you can cut the factory wiring and hook it into the system. Either way though the MSD box does not replace anything in the factory system. In May i just had an MSD box go bad on me when i was camping. Fortunately for me i used the plug and play harness and was able to just move the factory connectors back onto the coil and away i went.

Sounds like you've got a bad ignition module and or pick-up coil. The module is literally a five minute swap and only cost about $40.00.
 
OK, that makes it pretty clear then. I plugged the factory connector back into the coil and got nothing, guess I'm off to buy a new coil in the morning . . .

What about the ECM? I tried datalogging with the WinALDL program and could get no data stream (this is since I got the truck, not since it wouldn't start :doah:) so I took it to Lyndon Wester and he couldn't get any data either, so I want to figure that out while I'm in the mood for fixing :rolleyes:. His OBD1 scanner was talking to the computer, just no data stream.

Sure appreciate the help, guys, I've had to get my head around GM diesels and carb'd gassers, guess I'll be wrapping it around a whole new system again now. At least the basics stay the same :crazy:
 
If it runs good, with no check engine light, it's pretty unlikely it's the ECM itself.

If you do the paper clip trick (ALDL A-B pins shorted) do you get at least a code 12 from the check engine light?

Scott is talking about the pickup coil which is in the BASE of the distributor, not the external. You can test the exxternal coil (again not sure if that's on the troubleshooting page) as well as the pickup coil. The ignition module is the TYPICAL problem. Also testable. I can probably take shots of the troubleshooting/testing for that if wanted.

Make sure to look the wires and stuff over good though while you are in the dist. The distributors "guts" on these trucks seem to be increasingly reaching the age where they fail, so you should pay close attention while you are in there.
 
Slowly the pieces begin to fall into place . . . .:doah:I keep thinking that because of that fancy MSD stuff under the hood everything I know about these systems goes out the window.

Ok, so if I have power to the BAT terminal of the external coil with the switch in RUN, but no spark to any of the plugs, the problem is pretty much guaranteed to be either the pickup coil or ign. module. I do have the manuals, so I'll test them in the morning to verify before I buy any new parts.

When I jump the A and B pins on the diagnostic terminal, I get a code 12, nothing else.
 
So the ECM self check is good. Doesn't mean the ECM is good, but it's an indication. If you did a search here or anywhere where GM OBD1 is discussed, you'll see that the ECM is universally blamed and almost never the problem when people don't diagnose the system. Even my manual pointed me to the ECM, because the wiring all checked out good...turned out the connector pin lock had failed and the wire was backing out of the socket. :)

I can't recall how your ALDL connector is wired...could be that the data wire has been screwed with? How is the OBD1 device you tried using set up? I know on mine I've got to set the vehicle specs right (year, etc) or it won't work right necessarily.

ALDL on a laptop introduces a few other potential problems (COM ports, cable, etc) I've never had any problem with my OBD1 scanner connecting, I did with my laptop.
 
Well, as far as the ALDL datalog, it was Lyndon Wester of Wester's Garage using the scanner, so I'm pretty confident he knew what he was doing the the scanner. FWIW, Wester's Garage is the 'other' big name in TBI tuning. Not that it means anything about the ECM, just that I'm confident he knew what he was doing trying to get the data stream.

I've learned the expensive way how valuable proper diagnosis is--makes a huge difference having a resource like you guys. I'll keep you posted with my progress tomorrow . . . .

Thanks!!
 
Not much data stream if the truck isn't running but you can still see raw data with WinALDL and things like voltage should show up. Your guy most likely is useing a scan tool. Not sure what they show if a vehicle is not running.

To answer you ECM question yes they are the same except the chip.

The ignition module in the MSD distributor is the same as a stock GM and will interchange. I have seen more problems with the more expensive MSD than stock. This is the only fussy part of the EFI system that gives intermittent trouble. Have it tested at the parts store, ask them to do it three times. If it fails any it's bad.

Now my truck just started running bad when cold weather set in. All it was, was a fried distributor cap and rotor from all the extra sparks the MSD 6A box and coil puts out.
 
This thread seems to be getting pretty complicated for a simple ign module problem.
Just pull the module and have it tested like Eagle mark said.
While you are in the dist check the pick up coil if you want. Measure resistance between the 2 wires that come off the PU coil. Should be 500 -1500 ohms.
Replace the modue with an AC delco if you can get one. Stay away from the MSD modules they are crap.
 
eagle mark said:
Not much data stream if the truck isn't running but you can still see raw data with WinALDL and things like voltage should show up. Your guy most likely is useing a scan tool. Not sure what they show if a vehicle is not running.
Click to expand...

The data stream question was surplus. That was an issue before the truck quit, and the truck was running when we tried to get data off of it. Guess that's what I get for hijacking my own thread :doah:


Thunder--Yeah, I know, it's my fault for tackling multiple issues at once.
 
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