Turbo Performance

[Andy Clark]

It's me again. I seem to be full of issues today.
Here is my question- how does one tell if the turbo (1995 8.3C Cummins) is performing reasonably properly? I have no boost gauge (high on the "to do" list), so I cannot tell from boost readings. If the turbo is not well, would I note a serious lack of power on hills? How about black smoke from the exhaust? Neither indications have been observed.

This all started with investigation into why I am not getting any Filter Minder readings at all. Gerald previously advised that my Pat has a generous intake system and so might not show any indications until some higher level of filter occlusion is present. Because I'm a bit anal anyway, I changed the filter and even installed a new Filter Minder, but still no readings even after a trip over Snoqualmie Pass this past week. This led me to wonder- if the turbo has been "dusted" and is not "pulling" air as hard as it should, this could cause low airflow in the intake system and therefore a low vacuum reading. Yes? No? Maybe?

Also, a leak in the CAC and associated plumbing could have the same effect, but I hear no hissing noise from a pressure leak (although I listened only at idle). The tech at Freightliner had me rev the engine, but did not indicate that he heard anything wrong.

I throw myself on the mercy of you technical gurus.

Thanks

 Andy

[Edward Buker]

Andy,

I added a boost gauge to my 1989 Contessa in order to monitor the turbo performance. I could also tell when fuel was not being delivered properly due to a fuel system air leak which resulted in lower turbo boost pressure under full load. After I installed the boost gauge I found that without a load I could not see any boost pressure just by increasing the rpm while in neutral. I think it is a good diagnostic addition. If you are electronically injected you may not see black smoke under load. That was a symptom of excessive fuel delivery of a mechanically injected system. The fuel is better metered by the electronic sensing systems using an ECU (computer) that comes along with electronically timed injection.

 I do not know for sure how to tell if the turbo is delivering all of the boost that it should without a gauge, but if you did Snoqualmie pass and you held decent speed it would be a good indicator that the turbo was doing its job. The other possibility would be to go to a dealer with a Dyno (most Cat dealers have one) and have the HP measured. That will cost some money but it would provide a definitive answer.

Later Ed

[Andy Clark]

Thanks for the reply, Ed. I neglected to mention that I have a mech injected 8.3C Cummins, so are you saying that a deficient turbo would produce some black smoke since the fuel system would be delivering more fuel than the air necessary to properly burn it? There was no smoke that I could see in the mirrors.

As I recall I went over the pass westbound (steeper climb) at about 1700rpm in 5th.

Andy

[Gerald Farris]

Andy,
It sounds like you are trying to overanalyze a problem that does not exist. If there is a problem with the turbo on your coach, you will notice a very noticeable loss of power, large amounts of exhaust smoke, or oil coming out the exhaust. If you do not have any of these problems, your turbo is working as designed. I would expect the turbo on your coach to last at least 250,000 miles or more, so if you are not a high mileage coach owner, you will probably never need to replace a turbo.

Gerald

[Andy Clark]

Thanks, Gerald. As I mentioned in my OP, I tend to get a bit anal when analyzing problems and focus too hard on finding a solution.
Thanks for pulling me up on this. And yes, it sounds like I don't have a problem, especially at 60K miles. The only question I was getting at is has the turbo been "dusted", but I think you inferred the answer to that.
Thanks again.
Andy

[Edward Buker]

Andy,

That was great performance over the pass and Gerald is spot on as always. Andy you are right about the black smoke, without a well operating turbo too much fuel and not enough air. The point about mechanically injected systems is that they are not as precise in delivering fuel and at times, like when losing RPM during a climb, before downshifting it is likely that you would see some black smoke. Just the nature of the beast but not a problem if you do not.

VDO that makes a small turbo boost gauge. For a Cat 3208 this 0-15lb was a good scale. Not sure if you would need the 0-30lb, my guess is that the lower scale would be a better fit if you decide to go that way. I was able to mount it right in the dash center of an 89 Contessa. If you know your max boost pressures that are normal when things are running properly, you will also know when something is not quite right. This is more a diagnostic tool for knowing about problems with the fuel delivery system given that is the more likely culprit than any turbo issue with loss of performance, but it would show both.

http://www.egauges.com/vdo_ind.asp?Type=Turbo_Boost&Series=Vision&PN=150-1011

Later Ed

[Andy Clark]

Thanks, Ed. That link gets me to a mechanical boost gauge that rquires a tubing connection between a fitting in the intake and the gauge. Is that the kind you have?

I was looking for an electronic type that has a sending unit in the intake and wires connecting it to the gauge itself.
Andy

[Edward Buker]

Andy,

I ran a plastic tube given it was a simple system. It was not too much of a pain in that older coach
but each coach is different. I am not familiar with electronic alternatives.

Later Ed