6.5 Smoking....Sometimes????

[Flatlander6.2]

I just bought a 94 Chev with a non turbo 6.5. The previous owner claimed while driving, that the truck all of a sudden started puking greyish smoke. He assumed an injector had dropped a tip, and had the truck towed to a mechanic. The mechanic claims to have done a compresion test on one side of the engine, and they were all low, and claimed there was coolant in the oil. The truck was then parked and not touched or started for roughly 7 to 8 months.
This is where I come in. I was told by the mechanic that the truck was very hard starting and would need ether. However, after ten minutes with a set of booster cables, the truck started right up, and very well, no smoke, no chugging, ran like a watch. Once I got the truck home, I did a compresion test and was 410 to 420 across the board. The cooling system seems to be staying up as well.
Then after taking the truck for about a 60 mile drive, I shut the truck off to check everything out under the hood. When I started it again five minutes later with the engine still warm, it began to blow greyish blue smoke and it idled with some sporadic chugging and changes of RPM. Is this likely an injector problem, or the beginning of the end of my injector pump??

[Mark Rinker]

Could it be as simple as injector issues? How many miles on the current set?

[DmaxMaverick]

It could be as simple as a fuel system air leak, coupled with an intermittent fuel lift pump (and/or OPS). It could be the fuel injection pump, but they are usually less intermittent. If the fuel system is healthy, look toward poor grounds, and lastly, the PMD. Low battery voltage, or failing battery(ies) can also cause starting problems. The engine needs to crank at least 100 RPM's for starting. If the electric system is weak, there may not be enough juice available for cranking and electronics, required for a good start (indicated by your booster cable start). If the oil and coolant isn't swapping, your compression test results indicate an otherwise healthy engine.

A note on ether use.....
This is a last resort emergency helper. Ether should never be used on a glow plug Diesel engine, for several reasons. A mechanic who would use it on a GP engine is no Diesel mechanic. They should know better. You should pull and check your glow plugs. If they are original, or original series plugs (AC 9G, or Champion, Autolite, or Bosch replacements), they can fail, swell, and/or break off. This is without ether use. Ether will expedite this process. Not to mention a serious safety factor. If it hasn't been done already, they should be replaced with AC 60G, or modern "quick heat" type plugs. Many of our Supporting Vendors can help you in this regard.

[Mark Rinker]

Check your entire air intake from end to end for any obstructions, replacing the filter regardless of appearance.

Blockage can cause the intake tube to collapse under high demand, causing the turbo to spool down, blowing smoke and losing power.

Once the demand has subsided, certain blockage will then flow enough air to let the truck run normally at lower speeds, until hitting the magic CFM number, and repeating the cloud of smoke event.

Mouse nest in the fenderwell from a truck that has been sitting alot will do this, salt encrusted paper OEM fileter will do this, etc...

[Turbo Al]

My first vote goes for the mouse nest DON"T ask me how I know LOL
Then the OPS
then the fuel pump

As a side note I have never heard of a NA 1994 is this a pickup truck or a Van??

[Flatlander6.2]

This is in a 1500 pick up. The previous owner did not say that the engine was not the original, and I believe he was the original owner. The truck does have the vent holes on the front bumper on either side of the lisence plate, but I haven't followed them to see if they lead anywhere or not.
I now have about 500 miles on the truck and the smoking issues haven't returned since the initial one. I burnt off the old fuel, replaced the fuel filter and have been using a good dose of diesel conditioner. We're keeping our fingers crossed, I bought the truck cheap for the body and chassis and appear to have gotten a free engine out of the deal. Have only had the truck a week and could likely triple my money if I sold it today. By the way, what should the compression numbers be on a N/A 6.5? Should they be different than a 6.5T? It's running 425 to 440 across the board.

[DmaxMaverick]

The vent holes in the bumper are for additional cooling air. There should be a dam behind them to deflect the air toward the radiator. Don't block them!

Your compression numbers look ideal. The critical result is not necessarily the PSI, but the range of pressure between the cylinders. They should be within 10-15% of each other. No appreciable difference between 6.2, 6.5TD, and 6.5NA. The check should be done on a hot engine (at or near operating temp), at 6 puffs per cylinder test.

[rustyk]

As Mark mentioned above (I've had this issue twice on my motorhome, and only the second time was I able to correctly diagnose the problem), blockage in the intake will give this symptom by collapsing the rubber. In my case, the air filter was dirty, both times. I used to change it annually or 15K miles; now I change every 6K.