Possible misfire, or battery issue, or gremlins.

[thesameguy]

Hi all -

This is my first post here, but I've been reading these forums for years and years... but in 20 years of owning Suburbans I've just never had a problem I couldn't get through. This one, though, has be baffled. Sorry for the long post, but I figure I'll get all the details out -

I've owned this particular '99 K1500 for two years. Bought it with 168k on it, it ran quite well. About eight months or maybe a year after owning it, it developed what I think is a *slight* miss at idle - so slight you really wouldn't even know it if it wasn't for the other symptom... flickering headlights - at night, in perfect sync with the occasional miss, the headlights would flicker. Absolutely no reflection of this happening on the dash voltmeter. I ignored it.

About three to six months later I did a full tuneup on it - plugs, wires, cap rotor, filters, everything. This had zero effect on the miss/flicker, but it's a data point.

Maybe a year after that - we're now in summer of '16 or 1.5 years from purchase - the miss at idle grew worse to a miss at low engine speed - still almost undetectable, but in perfect sync with flickering headlights. Cruising at low speed through the neighborhood at night once every few minutes. I still did nothing.

Last fall I noticed the starter didn't sound as crisp - I don't know how better to describe it, but it was a mushy-sounding start. With no service history and the little miss I went ahead and replaced the coil. This actually fixed the mushy starts as well as a slightly rough shift to second which I could never explain, so good on me. No effect on the miss, however.

Fast forward to two weeks ago. Started it up one evening and it had a very poor idle, like the miss had gotten worse. The headlights were not flickering, but I could see the dash lights were unstable - pulsing with the miss. At this point I started thinking about things I should do. Once on the road, it ran and drove as good as ever - the slight miss, the headlight flicker, but nothing else new.

Over the past few weeks I've driven it four or five more times, with the same results - the cold start has a crap idle, dash lights flicker, then after a mile or two everything is back to how it's always been. Last night we added a new symptom - the AIRBAG light went on. WEIRD. After a shut down & restart, the light went away. This morning I decided to pull it into the garage for a full inspection - this time both the AIRBAG and CHECK ENGINE light came on in the short drive up the driveway!

I hooked up a Tech 2 - the CEL is for P0300, misfires and the AIRBAG is for B1061, the warning light failed its self test (LOL). I ran a live monitor of the sensors with the truck off and found some stuff I think is weird:

1. TCM reports 11.6v with the engine off - I feel like this should be battery voltage (will get back to this)
2. MAF reports 2.26 g/m with the engine off. What?
3. IAT reports 80 degrees (which it's not, but maybe is in the air box?)
4. CTS reports 74 degrees (which is about right, maybe 70 ambient)

I pulled off all the connectors for the ECM - it's spotless and clean in there. Same with the airbag module. If it's a connection issue, it's somewhere else.

Final piece of info: I hooked up a multimeter to the battery and got 12.7v with the engine off, which seemed unlikely. I looked away for a second and when I turned back the voltmeter said 8.x volts, but then climbed right back up to 12.7v. Okay, could have been me. I removed & reconnected the terminals and saw 11.x, 12.x, 12.7v. I am going to let it sit overnight and try again. Maybe the battery is failing internally? It's exactly three years old - made 2/14 - but I think it's a Walmart battery (PO bought it) so of unknown quality. Both terminals are spotless and clean - the ground wire to the body looks perfect. The engine bay in general is very clean, very original, and well-taken care of.

I feel like this could very well be a poor battery issue and will check that out tonight. However, I am a little concerned about the errant MAF and IAT readings... although maybe there are a symptom of screwy battery voltage as well?

I considered something like a vacuum leak, or an ignition or fuel problem, but I can't see why that would cause the lights to flicker, or especially the airbag *light* to not complete its self test. I am having trouble correlated the flicker, the miss, and the airbag light but am pretty sure they're connected.

Any helps/pointers/experience is much appreciated.

 

[Breakdown]

Sounds almost like a possible ground problem. Grounds will cause some funky erratic problems that will lead you on a wild goose chase. Clean sand and tighten all ground points between the frame engine and battery and any interior under dash grounds. The passenger side engine ground is garbage. Thin uninsulated flat strap that can corrode easily. Easy thing to do is pull the bolt on the alternator mount and Hook a battery cable with an eyelet on each end up to a good solid bolt on the frame that's fairly close and see if that improves it any.

 

[thesameguy]

I don't recall ever seen a passenger side engine ground - maybe that's a component here... rough description of where it is?

I'm in California - typically rust and corrosion aren't problems... but total failure still is!

 

[Breakdown]

Should be bolted to the rear most exhaust stud and connect to a bolt on the cab. There will be a strap as well that runs from the cab to the frame usually on the same bolt

 

[C30454]

As far as the running problem goes, you need to check the "cam offset" PID. Should be 0* +-2*. Usually I start having customers notice trouble at anything over 10*. If it is 13* or above, usually there are random misfires. Rotate the distributor counter clockwise to correct for a negative reading, clockwise if it is positive. Raise RPM's to 1000 so computer will re-evaluate offset reading.


Although you could have a ground issue, you more likely have an unstable voltage regulator. Unplug the alternator, start the vehicle, and see if your headlight flicker goes away.

Tom

 

[thesameguy]

Checked for the ground strap last night - I don't know how I never noticed it, but it's there and in excellent shape. Dusty but not damaged, oily, or corroded.

After 24 hours battery voltage was at 12.4v - I'm going to come back to it tomorrow. I still don't know why it read 12.7 in the first place, but a bad voltage regulator overcharging the battery definitely seems on the table.

I'll check the cam offset and see what it says - I don't think the distributor has *ever* been touched, so it should not be off... but you never know! My last GMT400 came from a generator tech who worked on a lot of Vortec-based generators, and he seemed to think distributors failed all the time!

Maybe related, does anybody know a source or part number for the seal that goes around the inlet side of the throttle body to seal the "hat"? It looks like a plastic body with an orange o-ring. Mine is very dried out and cracked/failing in places. Seems like something that needs to be addressed, but I can't find a part number (even for the entire hat!).

Thanks guys - I will report back.

 

[Breakdown]

Checked for the ground strap last night - I don't know how I never noticed it, but it's there and in excellent shape. Dusty but not damaged, oily, or corroded.

After 24 hours battery voltage was at 12.4v - I'm going to come back to it tomorrow. I still don't know why it read 12.7 in the first place, but a bad voltage regulator overcharging the battery definitely seems on the table.

I'll check the cam offset and see what it says - I don't think the distributor has *ever* been touched, so it should not be off... but you never know! My last GMT400 came from a generator tech who worked on a lot of Vortec-based generators, and he seemed to think distributors failed all the time!

Maybe related, does anybody know a source or part number for the seal that goes around the inlet side of the throttle body to seal the "hat"? It looks like a plastic body with an orange o-ring. Mine is very dried out and cracked/failing in places. Seems like something that needs to be addressed, but I can't find a part number (even for the entire hat!).

Thanks guys - I will report back.

Sorry it wasn't the ground strap but at least you know where your grounds are when you want to do the big three upgrade someday. Outside of that I'm not a vortec owner so I'm not sure what else it could be. Keep us in the loop I want to know the cure myself for future reference

 

[thesameguy]

No worries - I appreciate the effort. I will definitely follow up if/when I cure the issue - I hate when you find threads that don't have resolutions!

I am liking the idea of a failing VR on the alternator - it would explain everything. The dash gauge registers no fluctuations - but I have no idea how accurate or damped it is... maybe it just doesn't react fast enough to catch the sub-1s dives. I am going to dig through the box o' gauges and see if I have an Autometer, etc voltmeter in there tomorrow. Or maybe tonight - ain't got anything better to do.

 

[thesameguy]

Some more information:

This morning I noticed the PCV grommets in the valve covers were in poor shape, so I replaced them. I cleaned the valve itself, but didn't have a replacement on hand - I will probably do that just because.

Edit: I also inspected the air filter (good) and cleaned the MAF with CRC MAF cleaner just in case. The seal/o-ring on the hat is really bothering me!

Battery voltage this morning was 12.3v. Part of the reason it's been sitting is the rod from the driver's door handle to the latch popped off, so I fixed that this morning. The driver's door was open for about an hour, battery voltage didn't drop. Worth noting, maybe, is all the interior & running board lights are LED, so not a big battery drain.

Once I got it fixed, I started it up hoping the new grommets fixed everything - of course, no such like. Crap idle, no airbag light, but while waiting for the Tech 2 to boot up the CEL set. Bah.

I looked for a "cam offset" field but found nothing - there is a "CMP retard" field - perhaps that's it? If so, it's a 4 degrees. The other fields - IAT, MAF, BARO, CTS etc. all seemed about right. ECM voltage with the engine running was a steady 13.9/14.0v. Dash voltmeter was reading a hair over 14v - but I noticed this morning for the first time it shows about 11v when the battery shows 12.3v, so it's clearly not accurate. No surprise, the voltmeter in my TBI 454-powered motorhome is about the same.

I reset the light, took it for a drive to downtown, which is about 10 miles each way. Before I was 1/4 mile from the house the idle fixed itself and it was running same as it always has. When I got downtown, I plugged in the Tech 2 again just to see where things were - nothing seemed abnormal. I was at 1/4 tank of gas, so I decided to fill it up thinking maybe water condensed in there on the last trip to Tahoe - so that's a wait and see. I did a snapshot recording which I will post later on - maybe someone will spot something. The only thing that jumped out at me is that short term fuel trim is at 0% (just reset the DTCs?) but LTFT is at -14%. The A:F field does not *appear* dynamic, but was at 14.7:1.

The LTFT seems on the high side of normal. Perhaps I have a bad FPR or leaky injectors? Or, wait, a negative LTFT means enrichment I think, so maybe a vacuum leak? Either would totally explain a poor cold idle & misfires that improves when warm. Still doesn't explain the AIRBAG light and headlights flickering, but maybe they are legitimately unrelated.

 

[C30454]

Yes, the CMP Retard is the number I was referring to. Different software calls it differently sometimes. Is it 4 or -4? Should be 0 + or - 2. However -4 does not typically cause any driveablilty problems. We rarely if ever see a positive reading, so I can't say definitively that +4 isn't an issue, but I doubt it. Might as well zero it out just to make it within specs.

As far as the fuel trim, -14 means the computer is SUBTRACTING fuel to compensate for a perceived rich condition. Could be leaky injectors, FPR, or a host of other problems. A good thing to check is fuel trim #s at idle, and fuel trim #s at cruise. This can help narrow down the possible suspects. For example: Leaking injectors or FPR will have a big effect on idle fuel trims because the leak is a significant increase in the amount of fuel the engine needs at idle, but becomes insignificant at cruise because the engine is receiving so much more fuel that a leaky injector is only adding a minimal increase in the amount of fuel. So check your fuel trims idle and cruise and tell us what you have.



Tom