Working thru several no-start problems, fixed GP ghost, started, stalled, now nostart

[gtb]

First, vehicle info (haven't figured out how to create sig line yet):
1995 Suburban L65, mostly stock, utility model (rubber floor, vinyl bench seats, manual windows/doorlocks, etc.), PMD on finned heatsink behind bumper.

Refused to start last week, glowplug lamp (WTS) would not light, which gave a clue. Finally started after I momentarily jumped the two large screw terminals on the GP relay. I guess this freed up a sticky relay? GP relay is consistently working correctly now, GP light (pre-start) stays lit for a time that appears in accord w/ engine temp.

Resulting codes: 29, 62.

Ran fine for several days, until I noted minor bucking on the way home one night. The bucking seemed to coincide with driving over the expansion joints on the freeway, or other small bumps in the road.

Next morning, started fine, stalled sharply at 10 ft., started fine again, stalled again after 50 ft., would not start again.

Checked/cleaned grounds, esp. the two sets rear pass. side intake manifold, and the braided frame/engine/body straps.

Fuse inspection shows engine fusebox had some PO flakey addition, here is a photo:

The bare end of that orange wire was shoved into the cavity next to one of the legs of the Fuel Solenoid fuse (shown here sitting slightly crooked:

That orange wire energizes an (aftermarket?) relay on the firewall:

This solenoid power is supplied from the Aux B engine fusebox terminal. My guess is that this solenoid supplies the Tekonsha trailer brake controller. Is this common practice? Obviously the fusebox bare wire end "connection" is not accepted practice, but is the solenoid setup otherwise acceptable?

Back on topic--

Time allowing, I attempted to troubleshoot the no-start problem. Instrument panel lamps lit as expected, incl. GP lamp, good cranking speed. LP tested strong, approx. 1/2 quart in 10 sec. via the T-valve. LP would often continue to run 2-4 sec. after unsuccessful starting attempts. It really acted like bad PMD.

Bought a new PMD next day delivery from a best reputation supplier, swapped it in, still no start.

Carefully inserted paperclip in end of FSD extension connector to test voltage at pink wire, showed no voltage w/ ign. on.

Played with that Fuel Solenoid fuse in the fusebox, causing the Fuel Shut Off solenoid on the IP to chatter. Cleaned up and tightened the fuse receptacle, reinstalled the fuse, tested again the pink FSD extension harness wire (ign. on position), showed +12.34VDC! Getting closer! You can guess what happened next. Got the engine to start finally! Started several times equally well.

Resulting codes: 13, 81

On a hunch, swapped in the old FSD, engine started as well.

Remounted the (old) FSD/heatsink, engine still starts. Keeping the new FSD stored in the Suburban as a spare.

What can I do now to maximize reliability? Were the GP and fusebox issues related? The only thing I can think of is that it has rained heavily here recently and remember driving thru some big standing water a few times. Was the stubborn no-start condition really caused by a loose fuel solenoid fuse?

 

[TheDjost]

You would not be the first to have bad fuse connections cause a no-start condition. If you want you can clean the fuse spades, and put some dielectric grease on them. That should help the oxidation from coming back. I don't think the glow plug relay issue is related, but I'd think about replacing that glow plug controller. When I changed mine a couple of weeks ago, I took it apart, just to have a look-see, and the contacts inside were pretty badly damaged by the arcing that obviously goes on inside when the the circuit opens. The design doesn't seem very robust and tends to need replacing regularly.

 

[NVW]

On my 95 I had to bend the fuse spades on the fsos fuse to get contact.

 

[buddy]

That is an important fuse as you have found, powering both the fuel/engine shutoff solenoid and the PMD. Its nice to see you did your homework first as well and posted with good knowledge of the 6.5 fueling system and some troubleshooting. Also make sure all of your ECM fuses are cleaned nicely. When your GP issue started would you get all the other startup dash lights and the SES light?

I believe that solenoid is a glow plug override. Maybe there is a switch in the cab for it? Perhaps the PO had GP light ghost issues too.

 

[bk95td]

My money is on a glow plug overide or fuel pump overide. A brake controller doesn't need to be on a relay. The brake controller can be connected to one of the studs on the rear of the fusebox.

 

[gtb]

That is an important fuse as you have found, powering both the fuel/engine shutoff solenoid and the PMD. Its nice to see you did your homework first as well and posted with good knowledge of the 6.5 fueling system and some troubleshooting. Also make sure all of your ECM fuses are cleaned nicely. When your GP issue started would you get all the other startup dash lights and the SES light?

Thanks. Yes, all other pre-start lamps were lit except GP lamp. That's what clued me in to thinking "Hey, maybe it's not starting because the GPs are not working." I'll take another look at the ECM fuses. Same fusebox?

I believe that solenoid is a glow plug override. Maybe there is a switch in the cab for it? Perhaps the PO had GP light ghost issues too.

That's possible. Now that you mention it, previous to all this it seemed like the GP lamp could stay lit for a loooong time, even when the engine was hot. Actually , I almost never waited for it to go out before cranking the starter. But during my troubleshooting process, I thought it was not a GP override relay because when I fed +12VDC to its signal wire the GP lamp did not light. And the wire coming out of the relay's switched side appeared to go down the firewall and under the car toward the rear. If it was the GP override relay, it would have been energized whenever the Fuel Solenoid was energized, as its signal wire was jammed into the same hole. No switch in the cab. I'll have to dive under and follow where that orange wire goes.

 

[JMJNet]

So, the new PMD you bought did not solve the problem? and your old PMD did?

Is that means the new one is bad? If so, you don't want to store those as a spare. Exchange it? then try it and if it is good, you can use as a spare.

 

[buddy]

He said the PMD was not the problem, the problem was independent of either PMD he used. It started and ran fine with either.

 

[gtb]

After I installed the new PMD, the truck still did not start, so I looked closer elsewhere for the culprit. Jiggling the F.SOL. fuse made the fuel shutoff solenoid chatter when the key was on, so I chased after that. Fixed up the fuse receptacle, cleaned the fuse contacts, truck started after that. Thought the old PMD might not be bad afterall. Swapped it back in, started fine. Keeping the new one as a traveling spare.

Wasted $$$ on the new PMD (esp. the next day shipping) but sometimes it's like that. It gave classic symptoms of a failed PMD. Bucking, then sharp stalling, then no start. No codes, normal instrument panel lights on pre-start. Grounds looked good, plenty of fuel volume, etc. PMDs have a reputation so I jumped to conclusions.

Took the truck 150 miles today, no problems, started and ran fine the whole day.

 

[JMJNet]

Glad you fixed it. It is always good to have a spare PMD.

 

[JiFaire]

Glad you fixed it. It is always good to have a spare PMD.

Absolutely, and it's a very saleable item, too, so you should be able to get the largest part of your $$ back out of it if you wanted to.

Good work on getting everything running; you stuck with it to the end. Nice!

Corrosion on fuse terminals is an ongoing issue; lots of guys have had luck brushing things all clean with some AntiOx paste (the fuse tips as well as the receptacles) and making sure all the receptacles were tight. Loose or user-added wires are another issue - try to get the right spade connectors where possible, clean up and stabilize wiring so it isn't moving around (especially at the connections... tie it down before it gets to the box or relay).

I just hate tracing wiring or ground problems. You done good.

 

[gtb]

That orange wire energizes an (aftermarket?) relay on the firewall:
View attachment 23947
This solenoid power is supplied from the Aux B engine fusebox terminal. My guess is that this solenoid supplies the Tekonsha trailer brake controller.

And both bk95td an buddy suggested it was GP relay. I took advantage of good weather this AM and traced the thick orange wire back to the 7-flatpin trailer wiring socket, to the position of +12V. Why the solenoid was set to energize off the FSOS circuit, I don't know. I currently have it unconnected and may repurpose the relay as a LP or GP relay.