Pete Gossett
Pete Gossett MegaDork
9/1/18 6:26 p.m.

Where should I start attempting to troubleshoot a no-start/running rough problem that seems to have corrected its self?

Wednesday the Suburban died a couple seconds after it started, then took about 20-seconds if cranking to restart, at which point it was running really rough. It was the first time I’d started it in about 10-days. I had places to go & didn’t want to risk getting stranded, so I shut it off & left it until today.

Of course it started fine this morning, so I took it for a drive around the block & it seemed fine. I pulled it in the garage to give it a look over, but nothing seemed amiss. 

I thought about checking fuel pressure, but I didn’t see a nipple on the fuel line to connect a gauge. I know ignition modules have a high failure rate, but that wouldn’t be intermittent, right? Do these have the problematic under-hood fuel pump relays like the C4 did?

sergio
sergio Reader
9/1/18 7:39 p.m.

Fuel pressure for a TBI is around 13psi if it’s not close it will run badly. That’s where I would start. There’s not test port. You have to T a gauge into the line by the fuel filter. 

Pete Gossett
Pete Gossett MegaDork
9/1/18 8:55 p.m.

In reply to sergio :

Thanks!

Dusterbd13
Dusterbd13 MegaDork
9/1/18 8:55 p.m.

You can rent tbi pressure checker at orielleys. 

Also sheck the egr valve. Theyre bad about becoming sticky intermittently

RealMiniNoMore
RealMiniNoMore PowerDork
9/1/18 10:21 p.m.

I wouldn't dismiss the intermittent ignition module.

I got a free GMC Sonoma, due to a faulty ignition module. It just died while the PO was pulling out his work parking lot; he was "up to here" with the nickle and dime repairs." (Now ex-)step son calls me, asking if I wanted a free truck. I got there, got the keys, with no one else around, and it started just fine.

Long story, short, it ran great for a few weeks before it died and wouldn't start. Ignition module was the culprit. New module kept ir running for another year.

 

Pete Gossett
Pete Gossett MegaDork
9/2/18 6:03 a.m.

In reply to Dusterbd13 :

Oh, mines been throwing an EGR code since I got the truck last November. That’ll caus it to not run?

Pete Gossett
Pete Gossett MegaDork
9/2/18 6:04 a.m.

In reply to RealMiniNoMore :

Intriguing, good to know!

Patrick
Patrick MegaDork
9/2/18 8:53 a.m.

I had an intermittent pickup coil problem that resulted in a new distributor.  I chased it down by reading fuel pressure as it ran and had the problem with no pressure change, changed the module just because, and assumed it had to be the other thing inside the distributor.  I still have that distributor should you need it

Vigo
Vigo UltimaDork
9/2/18 9:12 a.m.

Oh, mines been throwing an EGR code since I got the truck last November. That’ll caus it to not run?

If EGR is wide open at idle it'll run poorly enough that it may stall. If you have a hand vacuum pump you can open it yourself and if the truck doesn't run worse then it's probably already open.. I think you can still look through the side of the EGR valve in those and see the shaft moving up and down too. 

Pete Gossett
Pete Gossett MegaDork
9/2/18 12:42 p.m.

In reply to Patrick :

Thanks for the offer! At this point I just hope it acts up again soon so I can try to pinpoint the problem.

 

In reply to Vigo :

I do have a Mityvac, so I’ll give that a shot. Honestly though it always runs super smooth, and the CEL doesn’t come on until after I’ve been driving at highways speeds for 5+ minutes. Even then it still runs fine.

This occurrence on Wednesday was a complete anomaly.

 

Kramer
Kramer Dork
9/2/18 5:29 p.m.

I second the pickup issue, although mine would occasionally sputter like it was starving for fuel.  It finally left me stranded.  I tested the pickup coil as per the factory service manual (using a D cell battery) to confirm my diagnosis.  A new distributor fixed it for about $89.  With a new brass cap and rotor.  

Pete Gossett
Pete Gossett MegaDork
9/10/18 10:20 a.m.

I drove the truck today to pick up a battery for my step-son’s car, and the truck definitely has a miss. It seemed to develop after the truck was warm, but was only really noticeable under part-throttle deceleration, or a couple times cruising 35-40. When I got home it smelled very rich, even after I shut it off.

So I’m thinking plugs/wires/cap/rotor/ignition module?

Vigo
Vigo UltimaDork
9/10/18 11:01 a.m.

Is there any way to make it misfire continuously? If so you can probably narrow it down to one cylinder using an infrared temp gun pointed at the exhaust manifolds where each port comes out of the head. 

If you have a multimeter you can just backprobe the o2 connector and see if it is actually running super rich. A look at the plugs would also tell that, plus if you pull ALL the plugs and one looks different than the others that may lead you to a problem area. 

Sparkydog
Sparkydog Reader
9/10/18 11:46 a.m.

A few years ago I spent many days chasing what seemed to be a fuel starving issue on a 97 C1500. Ultimately it turned out to be a low battery/low voltage issue that meant the fuel pump wasn't getting anywhere near 12volts. This would manifest itself in several ways. Either not enough total pressure to tell the ECU to start the engine, or it would start and run but then sputter at speed.

I only mention it as something to keep in mind - easy to check cranking voltage and charging voltage - something I did not do early on.

Pete Gossett
Pete Gossett MegaDork
9/10/18 4:20 p.m.

In reply to Vigo :

Thanks, I wouldn’t have thought to check the O2 sensor, though there’s no doubt as it’s running rich enough to water my eyes. I’ll definitely try my IR gun if I can get it miss at idle!

In reply to Sparkydog: 

That would have driven me crazy! The battery is 6-months old, but I’ll check the voltage just in case the alternator is failing. 

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