Why it's a good idea to install a Pyrometer & Boost gauge

[RaddCruisers]

Customer complaint due to recent changes in how their L300 is driving: Low power, fuel consumption has become worse, smokes more than normal.

Driving conditions: towing a trailer up and down the island, pulling the Malahat on a regular basis.

Result: Cracked exhaust housing on turbo, warped exhaust manifold, exhaust manifold gasket leaking.

Causes - suspected - too much throttle on hills and while towing a trailer, leading to excess exhaust smoke (read: HEAT) which has damaged the cast iron parts of the turbo and exhaust manifold.

Repair requires replacing the damaged parts of turbo and exhaust system, installing a pyrometer, monitoring fueling while driving and adjusting fuel at the injection pump as required. Setting the valves as required, adjusting the timing as required.

When running a pyrometer, one must pay attention to the exhaust temps and the acceptable temperatures depend on where the probe is placed.


Enjoy the photos...

~John

[mararmeisto]

That is, by far, the best explanation/demonstration of why running these vehicles as we are used to (with a NA model) is simply not a good idea - something WILL give.

Thanx John.

Ballpark - cost of parts and number of hours to replace? 2000$ job? More?

[jessef]

I've been pushing Delica/Pajero owners to install pyro's in their rigs for years.

Good examples.

On a side note, I've pushed our L400 with the 2.8L 4M40 diesel engine hard from Vancouver to Trail up hills/passes and it does an excellent job cooling. I used a boost gauge/egt pyrometer/oil pressure gauge to monitor what the engine was doing will pushing it hard. The intercooler/turbo and larger motor help a great deal. I was not able to push it into dangerous heat levels.

Unfortunately, the 2.5L 4D56T on the L300's/early Pajero's are easily pushed into dangerous heat levels in our driving conditions/roads.

Pyrometer is highly recommended. Not only will it change your driving habits (when to back off the throttle) but it will save your engine from cooking like the pictures here.

[RichD]

re: pics - wow. that is some serious heat damage

[RaddCruisers]

The repairs are in progress at the moment. The costs are actually going to be quite reasonable unless we find that there is other damage to the engine once it's running again. We really do try to keep repair costs as low as possible on these kinds of things, but it does take some time to get the parts in/out and do the appropriate testing.

This is, so far, getting off pretty lightly. If you run too high EGTs for too long, you're most certainly going to get into cracked cylinder heads and such. The head on this particular L300 has already been replaced once. The timing was set quite conservatively, so that is not part of the issue, it's really a matter of over-fueling while driving - ie: applying too much throttle and allowing all but the barest whisper of smoke to appear from the tail pipe.

The real lessons are: install a boost and pyro (as well as a good oil pressure gauge), keep an eye on your EGTs - there are lots of numbers tossed about, but if you keep it under 1050F with the probe placed pre-turbo you will be safer than not.

I'll try to update once we have completed the repairs.


~John

[Jensen]

Instead of a pyrometer I'm considering installing an air/fuel ratio gauge. This is based off of the recommendation of a friend who works at Westport, he says the response on a Pyrometer is too slow and it's too easy to get a bogus reading if the placement of the thermocouple isn't ideal. I can understand where he's coming from with the dyno tuning they do day in and day out, but I think it might be a bit overkill for just towing stuff and making sure I don't burn up my turbo. The price is about twice as much for the gauge and O2 sensor for a AFR gauge, and installing an o2 sensor is marginally more of a PITA. It would be really cool to have that in-depth of a view into what's going on with my engine, and if I ever want to play with things in the future it'll make tuning easier, so it might justify the extra time and $.

[mararmeisto]

That's all well and good to install a fuel/air mixture gauge, but how does one adjust the mixture? Obviously, backing off the pedal, but excess fuel doesn't burn out your turbo, too hot exhaust gasses do.

While it's true there will be a lag-time inherent in the system which will delay a cooling effect in the engine, but I think a pyrometer is probably a much faster way of determining a change in temperature in the engine than the water gauge on the dash (that's a slow response time).

[Jensen]

I dunno, the guy who told me that has been designing/building diesel fuel injectors for about 10 years for Cummins and Westport. I'm not saying the EGR thing is a bad thing but it's hard to take the opinions on a forum more seriously than an engineer who's bread and butter is dyno runs on Diesels. I know he's not a dumbass as I also used to work at Westport (in LNG fuel pumps so I have no clue about anything to do with injectors, turbo's, whatever. If you need to know how to pump a cryogenic liquid at 6000 psi though I'm your man). Anyways, I'll show you what he sent me.

"’Id get an air/fuel gauge instead of the EGT. EGT reaction time is bad - the guys here at Westport only use the EGT for steady state loading as they are pretty useless for anything transient which is the majority of what we use our vehicles for. You can use EGT as a tuning/warning tool this way but, not reliable for the driving we do. Because of the poor reaction time relying on an EGT to tell you when to get off the throttle can be dangerous as it will not represent what the actual running condition is until it’s too late (usually an extreme case). Air/Fuel will tell you if something is wrong very quickly, except it won’t tell you what cylinder has gone wrong, you will have to do that with cylinder cut out testing. So the Air/Fuel is more useful for trouble shooting whether a diesel or gasoline in a wide range of running conditions."

Then I sent him

"The only reason I might think an AFR gauge is excessive is because AFR isn't as crucial in a diesel. I'm not as worried about it going lean as it's not going to blow anything up (and I'm not going to dick with the turbo that much anyways so no big deal) and going rich just means I'm getting crap fuel economy. In a gas engine I totally see the value of an AFR gauge. If you lean it out then boom. Diesels don't go boom unless you're REALLY pushing it, and that's probably why the EGT gauge is more popular as they're cheaper."

Then he sent back

"That is a misconception as well. Everyone says that about diesel then they blow something up. AFR on diesel or gas is just as important but, usually the other way around. Too much fuel on a diesel means melted pistons whereas in gasoline you drop in torque. If you go lean in a diesel you drop torque. You could think of it this way – going lean: cranking boost, diesel = waste of time, you need more fuel but, you could drive around all day long with higher boost and it would not matter. Cranking boost, gas = BOOM!

I am sure Mitsubishi did their testing on these things. Something is not right, so trouble shoot then fix it.

How do we know the injectors are not leaking? If injectors are leaking or other internal parts are worn, injector open time will be longer hence dumping more fuel in (I can explain a whole bunch one day if you like but, it is amazing how many things can go wrong and on a regular basis). On a diesel - more fuel means more boost. When cylinder pressures rise due to the extra fuel and boost it can hold open the injector even longer, then you have a dangerous cycle that will only stop if you take your foot off it. That is why you keep hearing people with diesels say, “take your foot off it!” But, they do not know why, all they know is it works. I say, maintain it!

On top of all these issues (and there are more to the fuel system) the fuel will not burn fully in the combustion chamber but, will burn during the exhaust cycle and heat up your exhaust/turbo system causing damage. Remind you of some vehicle you know?

Boost gauges will tell you that you may be over fueling (because your boost is all of a sudden rising like mad) and really at this point it will provide you better information than an EGT. You just have to know what to look for but, no different than an EGT. But, in the end what comes first is 250 bucks for a Air/Fuel gauge which will tell you ahead of time what is going to happen, which will save you thousands."


Anyways, that's his argument and he's by far the most qualified injector/diesel engine guy I've met in my life. He's spent time at Dowop in Switzerland, he's worked at Delphi. It's hard to not listen to someone like that.

[mararmeisto]

So it's a toss up between an AFR or an EGT meter, because: So why is EGT important? EGT is an indication of how hot the combustion process is in the cylinders, and the amount of “afterburning” that is occurring in the exhaust manifold. EGT is also directly related to the air/fuel ratio. The richer the air/fuel ratio in a diesel, the higher the EGT will be. So again, it ends up being a matter of easing off the pedal.

From the reading I've seen, an AFR is more pertinent/particular to the racing world, especially in the gasoline-engine area, while an EGT is seen in diesel circles.

I'm not saying your engineer friend doesn't know what he's talking about, but again, the two gauges are telling the driver the same thing. This link gives a very good writeup on the whole issue: http://www.dieselplace.com/forum/archiv ... 36229.html

[Jensen]

That's kinda what I mentioned to him (the overkill aspect) I thought it might be a bit much and most likely more useful in racing. Also, the engines he deals with are typically found in semi trailers and even larger (gen sets) which see varying loads that are usually quite high. They really kick the sh#t out of them on the dyno's so maybe that's why he so pro AFR.