got a miss when cold

[rypie32]

hey guys,

I've read similar problems on here, but nothing quite the same...
when my truck is cold it has a 'miss'. Last night for instance, I was at work and went out to let it warm up for 15 min. before I left. It starts weird too-it always cracks right off, almost regardless of temp but it idles at about3-600 rpm and doesen't have the diesel clatter, I have to hold it at about 1/8 throttle to kind of let it sort itself out (lots of smoke), then all of a sudden the rpm's will surge and will idle at the high idle and regain the diesel clatter. If I don't hold the pedal down it will just sit there barely running at a low rpm-smoking to beat hell.....then.... When I took off it still 'missed', the thing that is odd is when you are steady on the pedal or very lightly accelerating it misses and has very little power. If I push the pedal down enough to down shift or unlock the converter it accelerates pretty good and the miss almost goes away or if I slightly decelerate the miss will almost disappear. If you just let it run for a couple minutes and take off, driving real easy it will smoke out the tail pipe and struggle to acclerate at all...after 5-10 miles it will finally snap out of it and will run perfect, the rest of the day unless it has sat for 8 or more hours in the cold then repeat the process.....It is in need of the routine maintenance stuff-filters and what not but this is baffling, could the filter harness or oil pressure switch do it?


thanks,

ryan

[RckyMtNDeZL]

Sounds like something in the fuel delivery department. Start it up and open the water purge valve while its running, see if you are getting a steady flow of fuel. That will rule out the pump. Your fuel filters could be trash, water in the fuel a few points of interest for you. Although I heard the pedal sensor can make it act weird too.

[rypie32]

Sounds like something in the fuel delivery department. Start it up and open the water purge valve while its running, see if you are getting a steady flow of fuel. That will rule out the pump. Your fuel filters could be trash, water in the fuel a few points of interest for you. Although I heard the pedal sensor can make it act weird too.

I've thought of that, but at 300+ bucks thats an expensive maybe...I'll try your suggestion. It is very consistent, you alway have to drive about the same distance to get it to gradually work itself out. I tested the lift pump with a gauge a couple months ago, the I.P. was replaced about 50,000 ago. The filter probably has close to 15000 on it. I'll start with that, thanks for the input.

ryan

[94Mule]

I had the same problem. What it turned out to be was a leaking injector or head gasket on #6 cylinder. It cost me a new motor. How many miles on the injectors? If over 100K, need to replace. That is from Walt himself. Mine had 125K on them. Check there first.

[rypie32]

I had the same problem. What it turned out to be was a leaking injector or head gasket on #6 cylinder. It cost me a new motor. How many miles on the injectors? If over 100K, need to replace. That is from Walt himself. Mine had 125K on them. Check there first.


thanks, but the injectors only have 2k on them or so just did injectors in december thinking that was the problem. The originals had 214,000 on 'em they were due....it helped the symptoms but that nagging hesitation is still there.........wtf!

[TAZZ9963]

Just an Idea, but what's to say that one of your new injectors isn't bad. just because it's new dosen't mean it's good.

[rypie32]

Just an Idea, but what's to say that one of your new injectors isn't bad. just because it's new dosen't mean it's good.

you aren't making me feel any better, ha! I was thinking though, my brother in law had issues one time with weak batteries causing his truck to stall....(my batts. are getting weak) I haven't had any stalls-but was thinkin' maybe with the increased load put on the alternator..coupled with a faulty optical filter harness would be causing this????? I don't know, I would be hard pressed to beleive it was an injector, because it does run better than it did....I'm gonna do some trouble shooting tommorow.

anyone else got an opinion?

thanks,

ryan

[ara4747]

First off, your fast idle should be set at 800rpm and should hold there without your help. Make sure your fast idle is engaging. As far as dealing with your hesitation and excessive smoke which I am assuming it is white. If after five to ten miles your motor runs perfect with no smoke, then your glow plugs aren't functioning on one or more cylinders. If the problem was with fuel delivery, it would do it all the time. It wouldn't matter if the engine was warm or cold. I read you installed the ssdiesel plugs, which are excellent glow plugs. Check your wiring to each plug. It sounds like one or two of them are not getting juice. Your engine runs fine after five to ten miles because the motor is getting warmer and is warming up the precombustion chambers where the plugs aren't heating. The precombustion chamber on 6.5must be hot, otherwise the diesel won't combust. It's takes a lot of heat and compression to ignite diesel.
If you want to run test to find which plugs are not heating, just start pulling wires to each plug and then start and see if it runs the same or worse. If it's worse, then you pulled the wire on a working plug. If it's the same, then odds are that plug isn't heating. Check the plug connections. I had the same problem as you after I installed new glow plugs (SS diesel Instant heat). It turned out I did not have a firm connection on some plugs and man did it run like crap and puff tons of white smoke until it warmed up. I fixed the connections and now starts like it's summer. Hope this helps.

[rypie32]

First off, your fast idle should be set at 800rpm and should hold there without your help. Make sure your fast idle is engaging. As far as dealing with your hesitation and excessive smoke which I am assuming it is white. If after five to ten miles your motor runs perfect with no smoke, then your glow plugs aren't functioning on one or more cylinders. If the problem was with fuel delivery, it would do it all the time. It wouldn't matter if the engine was warm or cold. I read you installed the ssdiesel plugs, which are excellent glow plugs. Check your wiring to each plug. It sounds like one or two of them are not getting juice. Your engine runs fine after five to ten miles because the motor is getting warmer and is warming up the precombustion chambers where the plugs aren't heating. The precombustion chamber on 6.5must be hot, otherwise the diesel won't combust. It's takes a lot of heat and compression to ignite diesel.
If you want to run test to find which plugs are not heating, just start pulling wires to each plug and then start and see if it runs the same or worse. If it's worse, then you pulled the wire on a working plug. If it's the same, then odds are that plug isn't heating. Check the plug connections. I had the same problem as you after I installed new glow plugs (SS diesel Instant heat). It turned out I did not have a firm connection on some plugs and man did it run like crap and puff tons of white smoke until it warmed up. I fixed the connections and now starts like it's summer. Hope this helps.


been a week or so since I've been on, but thanks for the input. A glow bad glow plug will make that big of a difference eh? I am still leary that that is the whole problem, I just changed the fuel filter, and when it is good and warm (ten plus miles) it still has episodes where it has a 'fish nibble' miss, you can't see it on the tach or anything but you can sure as hell feel it. If you accelerate it goes away, but static throttle speed or very slightly decellerating it has a slight miss...not all the time though. If you get it out on the road, like 100+ miles it will eventually snap out of it (so gradually that you don't notice) and never do it again until you shut it off for the night and is cold again the next day......? anyone have a similar story? I like the truck but this is driving me ape, can the ecm's go bad? throttle sensor? lift pump? the lift pump has an erratic clicking once in a while? dunno


HELP!

ryan

[rypie32]

crank sensor? maybe?

[ara4747]

Check the fuel return lines for obstructions and leaks, and perhaps the lines from the tanks. If there is an obstruction in the fuel return lines in it will run like it your saying. Also if there is a fuel leak in any part of your fuel line system it will allow air to come into the system. The fuel lines keep fuel through out the system by vacuum pressure. But if there is a leak in the system it can't create a vacuum and a lot of the fuel in the lines will drain back into the fuel tank thus putting a lot of air into the system. This will take an entire evening of sitting to do, 8 hours or so like you were talking about. Then when you start it up it will run like crap until all the air gets bled out. If the leak is bad enough and most of your fuel has drained back into the fuel tank, it could take up to a 30 minutes to get the air out. This sounds like a good possiblity for you because your diesel is showing all the symptoms for it. If you got a bad enough leak, even if you get all the air out, their will still be a very slight hesitation like your experiencing. Get yourself the Haynes manual on diesel repair. They layout a great way to check the lines for leaks. Go to the ssdiesel webpage and you can find it there or anyone of your local auto parts stores should have it. Get the Haynes manual not chiltons. Glow plugs are always the initial thought but since that's not it, the fuel lines are the next logical place. Hope this works.

[rypie32]

Check the fuel return lines for obstructions and leaks, and perhaps the lines from the tanks. If there is an obstruction in the fuel return lines in it will run like it your saying. Also if there is a fuel leak in any part of your fuel line system it will allow air to come into the system. The fuel lines keep fuel through out the system by vacuum pressure. But if there is a leak in the system it can't create a vacuum and a lot of the fuel in the lines will drain back into the fuel tank thus putting a lot of air into the system. This will take an entire evening of sitting to do, 8 hours or so like you were talking about. Then when you start it up it will run like crap until all the air gets bled out. If the leak is bad enough and most of your fuel has drained back into the fuel tank, it could take up to a 30 minutes to get the air out. This sounds like a good possiblity for you because your diesel is showing all the symptoms for it. If you got a bad enough leak, even if you get all the air out, their will still be a very slight hesitation like your experiencing. Get yourself the Haynes manual on diesel repair. They layout a great way to check the lines for leaks. Go to the ssdiesel webpage and you can find it there or anyone of your local auto parts stores should have it. Get the Haynes manual not chiltons. Glow plugs are always the initial thought but since that's not it, the fuel lines are the next logical place. Hope this works.

thanks,

that makes sense...I had an 85 burb w/ a 6.2 and had that problem. I never really thought about on my truck because it is a reasonably 'new' vehicle but 220,000 miles and 11 years ain't no where near new! ha! I'll check that out, if it is back siphoning or leaking, wetness would be the easiest first check I guess....thanks ryan :)

[brokenparts1]

Hey Missfire, You said a faulty glow plug could make a truck white smoke? I've just been attributing it to cold temps here in MI. My truck starts ok, not great. It cranks over 4 or so times, fires, but runs very choppy for a few seconds, then smooths out, but it smokes a alot of white/gray smoke for about 10 seconds, and sometimes it will miss and huff in the first 20-30 seconds. But after that it's all good. Any thaughts?
thanks ryan

[grancito]

my 6.2 with 250,000 miles, starts rough for 10 secs in a warm climate on Mexican diesel but starts rough as hell on USA diesel for up to 60 seconds. I put it down to uneven low compressions.

[6.5 MONEY PIT]

Hi all I had a very similar problem and what it turned out to be was the ops oil pressure switch 38.00 bucks located right behind or near fuel filter when I would first start the sub and let warm up for about 15 min. then start to drive and give it any kind of load on the fuel supply it would buck and carry on like it was missing or starving for fuel. this may not be your problem buy 38.00 bucks is a lot less then 300.00 good luck

[ara4747]

Broken Parts,

Yes, a faulty glow plug will make you puff white smoke. Now does it also do this during the summer or only during the cold winter? I know in Minnesota it gets down right cold. I would actually say there is a strong possibility that all your glow plugs are fine, the problem very well could be your glow plugs are just not staying on long enough. I live in Kansas and when it drops below 0 my glow plugs stay on for 12 sec. give or take. My truck would still puff white smoke for like 10 sec. I have installed a manual glow plug override so I can keep the glow plugs on longer. I now keep them on for 20 to 25 sec. on the really cold starts. My 6.5 starts cleanly with no smoke.
If you live in a really cold area I strongly suggest a manual glow plug override kit because your glow plug relay will not stay on long enough. Also make sure your glow plugs are self regulating, like SSdiesels instant heat glow plugs.
Otherwise the override kit will blow up your glow plugs.
So it's possible one of your glow plugs aren't working, but if the temp gets down there, I would have to say your plugs just aren't staying on long enough. Check out SSDiesels manual override kit. It's easy to install and works great.
Let me know if you need anymore info.

[Husker 6.5]

Of course, using the block heater definately helps on those 0* mornings, but even with the truck plugged in I used a little trick I picked up in the Army as a 1LT back in the day with starting the CUCV's (6.2L Blazers) on really cold mornings. After the WAIT TO START (glowplug) light went out, I would turn the key to off and remove it for a long four count. This would reset the plug timing circuit. Then put the key back in and turn to run to cycle the plugs again. The WAIT light would usually go out a few seconds earlier than the first time, and it would pop right over. A maintenance sergeant taught me that trick.

Apparently, it works with my 94, also. Three winters ago, after being 14 hours on a jobsite without starting the truck, and the temp down to -12*, I cycled the plugs four times that way, and it started, a little rough, but not bad for having a set of 11G's in the heads!

Anyway, if GM didn't change the timing and relay circuit for the glowplugs sometime during production, this trick may work for you,too.

[brokenparts1]

Thanks ara4747,
yah it's been really cold here lately, and its definetly been worse starting since it got cold. But its been a bit warmer lately, around 38 degrees and it still does it. My bigger concern though, is that right after it starts and it misses a few times, and after it quites smoking when it misses it puffs out a bit more smoke. It does this a few times within the first 30 seconds or so after a cold start. Is there a good way test glow plugs?
thanks again Ryan

[3bals]

A quick test is to use an ohlm meter. Unplug the glow plug and test it to ground. Either it has resistance (good) or is open (bad).

Jody

[rypie32]

Hi all I had a very similar problem and what it turned out to be was the ops oil pressure switch 38.00 bucks located right behind or near fuel filter when I would first start the sub and let warm up for about 15 min. then start to drive and give it any kind of load on the fuel supply it would buck and carry on like it was missing or starving for fuel. this may not be your problem buy 38.00 bucks is a lot less then 300.00 good luck


It's been a couple weeks since I've been on, great to see all the response's. I've got a OPS bought just gotta get it in....I've also noticed the fuel cap must not be venting properly, when I open it a rush of air goes in, that seems to be a contibuting factor but doesn't totally eliminate the problem.

thanks for the in put, 6.5 money pit - that's what I was hoping for, someone with a similar problem and a solution they found for it.

Also another way to test glow plugs is to use a 12v tester, put the aligator clip on the positive terminal, so when it is grounded the light comes on. now unplug your glow plugs, the spade should be grounded so when you touch it with the tester a good plug will light up the tester. Another alternative for someone that doesn't have a multimeter.

thanks guys!
ryan