Excessive Smoke

Just got home from a ten day trip in our motor home. About half way through began to belch exhaust smoke when heavy throttle was used at speed (like when going up a fairly steep grade). I have a boost gauge and EGT gauge and both indicated normal (6-8 lbs of boost and max of about 1100 degrees or less EGT) when the smoking would occur. As time went on the situation got worse.

Got home today and checked DTC (counting panel light flashes). Have a code 35, injector pulse width error - response time short. Also showed a code 78, waste gate solenoid fault, but I think this was left over from a problem I was having a few weeks ago with low or no boost which I was able to correct by snugging all vacuum and electrical connections and giving the solenoid a shot of WD-40 (per advice of John Kennedy).

Would appreciate any thoughts by those more expert about such matters before I place myself at the mercy of the local Chevy dealer.

Motor home, which I have owned since new in 1994, now has 248000 miles on it. The engine is a skirted block AMG new engine with about 70,000 miles. The injector pump was new with the engine which was installed by Peninsular.

This may sound simple....buttttttttttt....check the air filter and related pipes.

Will check out the air filter, etc. One other symptom is hunting which occurs during very light throttle decels at highway speed.

"Hunting" (or unusual up/down shifting) occurs when there is less than expected power at a specific throttle position.

When was the PMD last replaced ???

Normally the PMD just fails PLOP DONE... but I have seen pulse width error messages in conjunction with a failing PMD


If you have a good spare or a new spare it would not hurt to swap them and give it a go.

If that corrects the gremlin then mark the old one as GET YA HOME MAYBE unit.

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Originally Posted by BillCarry

...I have a boost gauge and EGT gauge and both indicated normal (6-8 lbs of boost and max of about 1100 degrees or less EGT) when the smoking would occur....

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Doesn't seem typical. I would expect boost pressure to drop and EGT to rise when more black smoke is seen.

I checked the intake system and replaced the intake filter. Plugged in a standby PMD. Neither had any effect on the smoking issue. Anybody got any other ideas or suggestions?

This is beginning to sound like an injection pump issue.

Possibly the fuel solenoid is getting HINKY (The actual fuel control valve...not the shut off)

Have you tried some fuel treatment?

Even a couple quarts of tranny fluid will clean things well.

It's a long shot, but I seem to recall someone who had a similar problem and it was cured by changing the fuel filter. Don't recall the specifics, and I know it sounds counter-intuitive; probably related to injection pressure, atomization, and/or timing. Or, it could be my oldtimers disease...

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Originally Posted by JohnC

It's a long shot, but I seem to recall someone who had a similar problem and it was cured by changing the fuel filter. Don't recall the specifics, and I know it sounds counter-intuitive; probably related to injection pressure, atomization, and/or timing. Or, it could be my oldtimers disease...

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I wouldn't call it a long shot. Most common issues are cured by simple routine maintenance items, such as filters, hoses, seals, and even the fuel filler cap. Always check off the pennies and nickels before throwing down the dollars.

Need to verify if I am right. A short pulse width would mean a longer open time for the solenoid and thus the excessive fuel flow; is that correct?

Also the pulse signal comes from the computer, amplified by the PMD; is that also correct?

Seeing as I have already changed the PMD it would seem that I either need a new computer or injection pump. Any ideas on how to determine which one might be at fault?

Finally can anyone recommend a good 6.5 turbo shop in the Detroit metro area?

Thanks for the help.

Although it is sometimes labelled as "pulse width", that is not what is being measured and reported by the PCM. That parameter is the RESPONSE TIME for the solenoid valve to go from open to closed or closed to open. If you watch the values with a scan tool while operating, you will see that they fluctuate between 2 and 3 milliseconds regardless of actual fuel flow. If the response is too long, that means that the solenoid or the valve is hanging up and not moving quickly enough. If the response time is too short, it means it is moving quicker than it should and may indicate a worn bore which leads to fuel leakage.

Both problems affect injection timing and thus, performance.

If you didn't have a boost gage and weren't reporting normal boost numbers, I would say that the you lacked air from an inoperable turbocharger (wastegate issue). However, with that ruled out, I would go with John's advice on the fuel filter. Check that out.

I replaced the fuel filter but that didn't have any effect. It still smokes like a bandit when you push it hard. I no longer are getting the pulse width code by the way..???????

Is the Code 35 back?

No. There are no codes showing now - which surprises me.

Sounding like injection pump.

Get a couple cans of fuel treatment, or some ATF in the fuel.

If the fuel metering valve is having issues the extra lube in the fuel may help.

If the issue gets better then a fresh IP is likely in Order.

I put a couple of bottles of Stanadyne Fuel Conditioner in about 40 miles ago. No effect so far.

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Originally Posted by BillCarry

I put a couple of bottles of Stanadyne Fuel Conditioner in about 40 miles ago. No effect so far.

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Using ATF (or 2 cycle oil, as I prefer) does 2 things, in addition to the increased lubricity. The higher level of solvent/detergent quality helps clean the internals, and increases the viscosity (which the additives don't do). Increased viscosity helps a tired pump with increased tolerances make pressure more easily. However, if you aren't having issues with hot starts, it isn't likely to tell you anything, as viscosity is probably not the problem. At the same time, 40 miles is hardly enough to see noticeable results. Often it will require hundreds of miles, if not a thousand or two, depending on the severity.

I agree 100% with DMAX

Sadly there is little that can be learned from scanning the rig while it's running that will give a definitive answer.

As RJ mentioned you can watch what the fuel solenoid is doing as far as the opening and closing data.

IF you can get a good tech tool on the rig and drive it...then take a look at the fuel solenoid action while cruising, and then get the engine under a load and see if things get strange.

AS FAR AS THE ATF thing goes, I would dump in a gallon of it at about 1/2 tank of fuel.

These engines will run fine on pure ATF in moderate temps.


Really the only good way to see whats up is to MARK THE IP TO timing case with a sharp scribe line at the mounting flange (To locate) and then yank the pump off and get it to a shop that has a Stanadyne pump tester and see what things are doing.


The other thing that comes to mind is possibly you have a bad injector/s ...
Bad squirts can start peeing a stream rather than a nice spray pattern.

Bad squirts can cause lottssa smoke and BIG HEAT.

1100 F is really more than I like to see more like 1000 F max with the thing working real hard.

A single bad injector that's dumping fuel in puddles rather than a fine spray can cause what you describe.

Yank the Squirts out and get them tested for POP pressure and spray pattern


A bad squirt can drill a hole in a piston right quick... BAD JU JU...

I had a 94 Burb with bad squirts and it would kill an entire swamp full of skeeters when ya leaned on it hard