thesameguy
Newbie
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.
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.