Lack of power and black smoke.

crazy4two · Post by **crazy4two** » Mon Jan 16, 2017 2:05 pm

Hi there, newbie here, just picked me up a 1991 L300 with the diesel motor. The car runs great when puttering around town but as soon as I get it onto the freeway and into 5th gear is slows down if going up even the slightest grade of the freeway then when I step on the gas it omits a big cloud of black smoke from the tailpipe until I let off the gas. I go from traveling 110 km/h down to like 80 km/h.

I've searched the forum and tried a few things including lubricating the blow back gate and verified it is opening and bleeding the fuel lines but did not seem to fix it. Maybe a little but still there.

As I step on it it almost sounds like an exhaust leak. If it has an exhaust leak could that be the problem? When I bought it the guy had recent exhaust work done and when I examined it I noticed that the flange connecting the bottom of the turbo unit was attached but not bolted down so I bolted it down but noticed no gasket there so is it supposed to have one?

Anyway any suggestions or guidance would be much appreciated. Thanks.

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Post by **FalcoColumbarius** » Mon Jan 16, 2017 4:10 pm

Are you driving a manual transmission wagon? You need to gear down when climbing hills. Remember that you are driving a diesel that has 86 prancing ponies under the bonnet, not a GTO. When working harder up a hill, a diesel is likely to dump a little soot but sometimes the fuel screw has been adjusted and there is less air getting to the combustion chamber by comparison to how much fuel is going in.

The first thing I would check is your air filter element, how white it is. Hold a trouble lamp against the side of the filter element and see how much light gets through to the centre, it should be quite bright inside.

Falco.

Lapprentis · Post by **Lapprentis** » Mon Jan 16, 2017 7:40 pm

Dont know about the black smoke but my Van (automatic L300) is healthy and will slow down on every hills

Depending on the slope, 60 to 80 KPH is common while climbing...That is the way you have to drive these

That is why you have to installed an EGT gauge so that when the engine can not give you more "juice", you ilft your foot of the gaz pedal so that you do not blow your engine head gasket

Lapprentis

crazy4two · Post by **crazy4two** » Tue Jan 17, 2017 8:02 am

Thank you so much for the responses and I will check that stuff but it sounds like it may be pretty normal which is somewhat comforting. Also I will search the site for info regarding installing an egt gauge. Thanks again.

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sk66 · Post by **sk66** » Tue Jan 17, 2017 2:19 pm

crazy4two wrote: As I step on it it almost sounds like an exhaust leak.

The over-pressure dump valve? When I got mine it was popping at ~ 8-10psi boost so even a minor incline was an issue. Replaced it w/ a new one which pops at ~ 13psi. Secured it so that it can't pop and I max out at ~ 16psi...

Post by **Growlerbearnz** » Tue Jan 17, 2017 6:22 pm

sk66 wrote:The over-pressure dump valve?

You might be onto something there. A pressure relief valve that's opening too easily would account for the symptoms: Works fine until it pops, and then black smoke because the injection pump doesn't know that most of the air isn't making it to the cylinders.

I'd try wrapping it tightly in electrical tape (lots of tape) to temporarily seal it, and see if it makes a difference. It's on the inlet manifold at the back, and you can *just* reach it without removing the drivers side engine cover. Here's a picture of mine sealed up/disabled with green heatshrink (and an inset of what it looks like when removed):

: PRValve.jpg (304.17 KiB) Viewed 4643 times

sk66 · Post by **sk66** » Fri Jan 20, 2017 11:15 am

Growlerbearnz wrote:
sk66 wrote:The over-pressure dump valve?
You might be onto something there. A pressure relief valve that's opening too easily would account for the symptoms: Works fine until it pops, and then black smoke because the injection pump doesn't know that most of the air isn't making it to the cylinders.

And a severe lack of power. For some reason when it pops it's not "regulated," the boost pressure will drop well below the pop-off point... at least mine did.