I have been asking some questions about an uneven running engine/weak cylinder condition in the past week in this thread: Are these symptoms of injector or harness failure?

But I had an interesting (to say the least!) cold start experience in the last week that I wanted to throw out for comment. The truck is a 2001 F350 7.3L, stock, CPS replaced in Dec '08.

To set the stage, I usually do at least 2 hours of pre-heat when temps drop below 20F overnight. May not be necessary, but we keep 15W40 oil in year 'round since we go to warm areas for work even in winter. (We live in the western VA mountains.) We went to OH last Sunday, into a cold snap, and on Monday AM, I only had time for about 50 minutes or preheat. The outside air temp was 9 F. At start up, there was diesel knock on one cylinder that was absolutely HORRENDOUS; sounded like an ex-wrestler banging on the block with a sledgehammer as hard as he could, and I almost shut the engine off for fear of damage. This is my 3rd diesel, and in all my cold start experiences, I never have heard anything like this. After about 20 seconds of this, it gradually subsided to a normal range; that particular cylinder knock continued to be louder than the rest, but normal for a very cold engine. The engine never run ragged or partcularly uneven that I could tell during this start-up cycle, and there was only what looked like an smooth output of white water-vapor smoke out of the exhaust until it had warmed up a bit.

So, what is UP? I was wondering if this could be due to some injector pre-injecting when cold, or stuck and dribbling out excess fuel that caused a detonation condition. But that's just some guesses. Any input on what casued this, would be appreciated. Any one else have this type of cold start experience?

And, I have always noticed a louder than normal cylinder knock on one cylinder ever since I got this truck with 18k miles on it. I never paid it any mind, as this seems to be typcial on other engines of this type that I have listened to. But is it normal?

Thanks in advance,
Mark B.

 

sounds like a piston slapping, goes away after the piston warms and swells to normal operating size.or a injector not working right till oil pressure builds up, just guessing thou.

 

It's a combination of mileage, oil weight, and temperatures.

Higher mileage injectors will tend to "stick" a bit when cold. You can verify this with an injector buzz test on a cold engine. A sticking injector will buzz very quiet the first few times, then begin to get louder if you repeat the buzz test.

Next is oil weight. Injectors in Powerstrokes are HEUI (hydraulic electric unit injection), meaning they rely on high oil pressure to fire. If you have a heavier weight oil, and in particular if that oil is cold, then you change the way the injectors fire. This can alter quite a few things, including timing, contributing to louder engine knock.

Last of course is temperature, which ties directly into injector mileage and oil weight. However, there are other factors at work when temps are lower. One factor is that the timing is automatically advanced by the PCM when the engine oil temps are low. This advance increases engine knock, even on a newer engine.

So the noise that you heard does happen, and it's probably a combination of all 3 things that lead to that one injector knocking more than the others. You also mentioned one cylinder that has always been louder than the others, even at only 18K miles. If it's the #8 (rear driver's side cylinder), then that's normal. The #8 cylinder has a long lead injector, meaning a larger pilot shot. With advanced timing in cold weather, that larger pilot shot has a greater explosive force and you'll hear an increased knock.

Changing your oil to a synthetic will greatly reduce that knock at startup. Synthetics aren't as thick as regular dino oil in cold weather, but in warmer temps they operate just like dino, so it's a win-win situation there. The drawback of course is cost, as synthetics are a bit more expensive.

 

Could a dead glow plug or two also be a possibility? With a dead glow plug, that cylinder may not be warming up and allowing full combustion to occur.

 

Hey, Mark. You've got me worried. From what you described, I'm wondering if you had minor hydraulic lock? That would be caused by a liquid in the cylinder which cannot be compressed. It would be only slight or you wouldn't have been able to start the vehicle. The worst result of this could be a bent rod. If an o-ring or head gasket is weeping, cold weather could increase the amount of fluid leaked. Unfortunately there are quite a few ways for a fluid to get in to the cylinders. I would suggest that you get it checked out soon to be sure that hydraulic lock isn't the problem.

Oh, yeah. Welcome to FTE!

 

Thanks to all for the reply.

Flamebuster: Yea I have been wondering about piston slap and wrist pin slap for about 50k miles with this engine, but it would not come on like it did at just 1 startup cycle, IMO. And, I suspect it would have been getting worse and worse over that many miles due to wear. And all this has been coincident with more uneven engine running on one cylinder over the last several months. So I suspect timing or injection or harness issues.

Pocket: Your explanation matches mostly with what I was thinking. This horrendous knock subsided very quickly (in < 5 seconds time) at about 20 seconds after start, so I am wondering if the ECU pulled out some of the timing advance at that time, or a sticky injector loosened up. And thanks fo rthe explanation on the role of oil inthese injectors; makes sense with the oil we have run. I'll try a change to synthethic while it is still early springtime and still cool; we use synthetics in all our gas engines and racing engines. I've avoided it in the diesels due to wanting frequent changes.

Ponyboychris: I'll check the plugs, but I expect I would have seen the white smoke associated with unburned fuel when there are cold cylinder misfires.

Farmdad: Well, you may have a point. It sure sounded like a severe compression knock. (Or like a gremlin snuck in and fully removed a rod bearing, and then put it back gradually after 20 seconds!) The engine is not using coolant or using excess oil; I put in a quart of oil about every 1.5k miles. And when cranking that AM, I don't recall any momentary hangups while spinning the engine over with the starter before it fired; I would expect it to hang or slow for a moment when meeting the minor hydraulic lock, like you sometimes find when cranking a very hot, high compression gas engine.

Thanks to all for the input. This did not occur the next AM when it was 13F, but I pre-heated it about 5 hours. The eninge started and sounded like a normal but cold diesel.

Regards,
Mark B.