Intermitent cold misfire on one cylinder

[moose60]

I am very happy with my pickup overall, but there is one thing it does that has started to bug me. When started for the first time for the day, it fires right off on four cylinders. Immediatly it begins (I think) to misfire on one cylinder, in a semi-regular patern. Once or twice a second I feel a small shudder and get a puff of smoke from the exhaust. In 20 or 30 seconds, the truck runs smoothly and never really smokes again. My electrical multimeter seems to have died while rattling around in my tool box, so I have not been able to check the glow plugs. Should I perhaps try bleeding the fuel system again, or just pony up some cash for another multimeter(I will need one someday). Should I eliminate the possibility of problems with the glow system before I worry (late at night while trying to sleep) about sticking injectors etc.

One final question: If I do wind up replacing one (some?) of the glow plugs, can I mix slow and fast glow types? I read the post on SD22 glow plugs, and didn't see any info on this. I suspect I can't mix.
Byron

[EvergreenSD]

I have very much the same problem with my SD22 though perhaps a bit worse than yours. Actually, since it's been hot here the missing isn't as pronounced but I do get more smoke than I ideally would on warm up but when the weather was cooler I had the same miss with individual puffs of smoke and shudder while trying to cold start. This would continue for a minute or more before I learned to gently feed it a little throttle to help it warm up. I've been kind of assuming that it's injector related but I really don't know. I did replace my glow plugs and it helped a little but not much. The strange thing is that it would start easily and then miss. If there was a glowplug out I would expect it to start a little harder and miss right from the start. I'm certainly interested to hear what you find out.

[philip]

SNIP
When started for the first time for the day, it fires right off on four cylinders. Immediatly it begins (I think) to misfire on one cylinder, in a semi-regular patern. Once or twice a second I feel a small shudder and get a puff of smoke from the exhaust. In 20 or 30 seconds, the truck runs smoothly and never really smokes again.

For the moment, let's assume you are cold starting the engine immediately AFTER the Glow Plug light goes out.

If you raise the engine RPM only a LITTLE, does the engine continue to run on all four without misfire?

a) Yes. Then for the moment we can set aside air in one or more injector lines.

b) No. If the engine starts misfiring (puffs of raw fuel exits the exhaust pipe) as the idle is raised, then you have a heat insufficiency in the combustion chamber. This can be a due to a marginal glow plug or one that is caked in carbon and strangely just plain cold fuel. This assumes you do not have some mechanical deficiency such as compression well below minimum spec.

Cooler ambient temperatures will bring on this behavior in perfectly healthy SDs. 'Cooler' means room temperature. Try cold starting your truck on a 70 degree morning with the White/red glow plug harnass wire unplugged. You will crank and crank and crank. These things want HEAT to get going.

Looking at the combustion prechamber, you'll see the fuel injector sprays directly on the hottest part of the glow plug. Colder air and colder fuel serve to quench the glow plug. Raising the RPM increases the spray of cold / quenching fuel over the glow plug.

My electrical multimeter seems to have died while rattling around in my tool box, so I have not been able to check the glow plugs.

Testing for resistance is not reliable enough. See: SD22 Glow Plugs

SNIP
One final question: If I do wind up replacing one (some?) of the glow plugs, can I mix slow and fast glow types? I read the post on SD22 glow plugs, and didn't see any info on this. I suspect I can't mix.
Byron

Information about the SD25 AutoAfter Glow System and SD25 glow plugs: SD25 Glow Plugs

You may NOT mix SD22 and SD25 glow plugs in an SD22 (Type I auto glow system). If you do, the SD25 glow plugs will turn to toast in fairly short order because they are designed to heat VERY quickly and then be shut OFF within 7 seconds by the AutoAfter Glow System (type II). They do not get significantly hotter than the SD22 glows.

[moose60]

If I do not raise the RPM the truck will die, when I speed it up slightly to moderatly it stilll smokes and shudders. Yes, I am starting Cold, immediatly after the glow plug light extinguishes.

My question in regards to glow plug type refrenced the link to a glow plug vendor (I believe the link is on the SD22 Glow Plug Experience page) that refered to both a normal, and a sheathed or faster type for the SD22, which seemed to differ from the 900*C regulated type used on the SD25.

The truck only has 130k miles, so I *hope* that I have no issues with compression etc.
Thanks for the reply.
Byron

[asavage]

The strange thing is that it would start easily and then miss. If there was a glowplug out I would expect it to start a little harder and miss right from the start.

I had a hole in an SD22 glowplug and that was my symptom. I don't recall if the problem went away completely after replacing that bad GP. I didn't replace all four of them, like I would today.

[philip]

If I do not raise the RPM the truck will die, when I speed it up slightly to moderatly it stilll smokes and shudders. Yes, I am starting Cold, immediatly after the glow plug light extinguishes.
My question in regards to glow plug type refrenced the link to a glow plug vendor (I believe the link is on the SD22 Glow Plug Experience page) that refered to both a normal, and a sheathed or faster type for the SD22, which seemed to differ from the 900*C regulated type used on the SD25.
The truck only has 130k miles, so I *hope* that I have no issues with compression etc.
Thanks for the reply.
Byron

The "sheathed" type is the supercede model. The only "stock number" offered for the SD22 is 1232 (Y-112TS)

[moose60]

Well... I pulled the glow plugs tonight and fired them up at 12V. They all smoked, and then began to glow. None seemed to have any type of physical defects. The second one from the front is a pain in the butt to remove with all the injector lines in the way.
I'm considering trying to find a helper tomorrow, and cracking injector lines while the helper keeps the motor running.

[asavage]

The second one from the front is a pain in the but to remove with all the injector lines in the way.

You think that's bad, you ought to try to do a compression test via No. 2's GP hole! See this post for details.

[moose60]

Yeah, I read that post about compression testing via the glow plug holes. I'm only worried about this misfiring problem because it creates an embarrassing amount of smoke first thing in the morning. I also don't think that it will get better as the weather cools off this fall. Any more ideas? Thanks for all the help so far.
Byron

[philip]

SNIP
I'm considering trying to find a helper tomorrow, and cracking injector lines while the helper keeps the motor running.

720 diesels have a throttle lock knob to the left of the steering colum (looks like a "choke" knob). Turn left, pull out to set RPM, turn right to snug/lock.

Air in these lines self purges in short order. So what are you hoping to accomplish?

I agree with your notion that cold start-up roughness and smoking will get worse as overnight temperatures decline.

When you are sure all four glow plugs are operational and that compression is within tolerance, then it is time to examine the injectors for internal leak down (pintle wear and/or carbon accumulations) and spray pattern. Unless you have a "pop-off" tester for the injectors, just remove them and have a diesel shop rebuild them. For the labor money, it is NOT worth cleaning them.

SD22 Injectors

[moose60]

Since I have only once a day (the first start) to experience this problem, things progress slowly. I have changed my definition of the misfire to include "surging". I tried to use the minimum throttle possible to keep the truck runing. This is when I noticed a fairly pronounced surging without any movement of the pedal. Does the surging ring bells in anyones head?

[philip]

Since I have only once a day (the first start) to experience this problem, things progress slowly. I have changed my definition of the misfire to include "surging". I tried to use the minimum throttle possible to keep the truck runing. This is when I noticed a fairly pronounced surging without any movement of the pedal. Does the surging ring bells in anyones head?

Yes. Does this 'surging' persist with engine at operating temperature?

[asavage]

I think you're experiencing the pneumatic governor in operation there. As one or more cylinders do or do not contribute to the whole, the volume of airflow through the throttle body rises & falls, and that influences the pneumatic governor to change the fuel feed volume. IOW, the surging (engine speed changing up & down, with the accelerator in a fixed position and with a fixed load on the engine) is a symptom of one or more cylinders firing only intermittantly.

Yeah, I've experienced it here too.

[moose60]

The surging does not persist more than one minute. Once warm the truck runs great. The warm up throttle slips, so it isn't any help right now. My cursory exam showed no obvious cause for the slippage. Thanks for the help guys.
B

[philip]

The surging does not persist more than one minute. Once warm the truck runs great. The warm up throttle slips, so it isn't any help right now. My cursory exam showed no obvious cause for the slippage. Thanks for the help guys.
B

Ok, so there are two complaints.

1) random misfiring which is likely due to marginal heat generation in the combustion chamber or possibly air in the high pressure injection lines from leaking injector(s).

2) engine RPM surging that may be due a leaking and/or stiffened Pneumatic Governor diaphragm, air leaks in the pneumatic governor vacuum line, faulty EGR operation, or highly fluctuating fuel delivery pressure.