GM 4106 power question.

[bluehair]

First post here. My 4106 has an 8V71. I was headed westbound on I-90 over Snoqualmie Pass a couple of weeks ago when I could not get the speed to stay up to where it is normally. Going over the pass that direction is easy, the hills are not that bad and I have never had this trouble before. So, the RPMs were just getting lower no matter how much foot I used on the throttle. I don't know if this was a fuel problem or a throttle problem. It worked fine once it built speed back up going down hill on the west side of the pass.

Where should I start looking? 

[Lin]

I would check the fuel filters first.

[Eric]

As already stated check your filters! I was having the problem time and time again kept on changing em! turned out i had alge in our tank!

[DMoedave]

Fuel and air. Check filters and pickup tube possibly. Has she been sitting long? How old is the fuel? Good luck.

[bluehair]

This coach sat for a few years after the man that did the conversion passed away.  So, that might be the problem. Can I change the filters myself, and if I do it, do I need to bleed the lines like I had to do as a kid on the farm when I would run the tractor out of diesel?
I'm not as familiar with this engine as our old tractor.

[Madmike]

Fill the new filters with fuel and then just swap them out.

[Barn Owl]

I completely agree with everyone, change your fuel filters. It is a DIY job. Do you have cartridge or spin on? If you don't know then post a photo of your engine compartment and we can tell you. Fill whatever you have with clean diesel before installing. You should not have to re-prime. When you restart grab the throttle and keep the RPMs up for a little bit. (Easy to do on a GM). That is what the old time two stroke mechanics do.

[Ed Hackenbruch]

When you do change your fuel filters only do one at a time or you stand a good chance of losing prime.

[Len Silva]

Before you change the filters, make sure you are getting full throttle.  It's a two person job but very simple to do.  I had problems with the cable slipping out of adjustment on my 4104.

[OneLapper]

If all of the good advice above fails, read this post.  I fought with this same problem for a VERY LONG time.  This is what my problem was.

http://www.busconversions.com/bbs/index.php?topic=11011.msg114691#msg114691

[bluehair]

Today I cleaned the air filters by blowing the out with a compressor. They had a lot of really fine powder that looked like ash from Mt. St Hellens circa 1980. I know it's not because these filters were put in during the conversion. I spoke with a friend tonight who told me to get a product from Lucas that will kill the stuff in the tank if there is any. Another friend turns out was a diesel mechanic in a past life and will help me with the fuel filter issue. He felt that given the altitude that air might have been the problem. We'll change the filter on the fuel and I will buy new air filters. I hope that takes care of the problem.

Then I can start on the leaks!

[TomC]

Bluehair- it is a big no-no to blow out an air cleaner (paper type) because you can put small holes into the filter elements from the high pressure air.  Then you have little holes that raw unfiltered air can get into the engine.  PLEASE- buy a new air filter ASAP!  When the air filter gets dirty-just replace it.  I have a filter minder (air restriction gauge) on the air filter that tells me when it needs to be replaced (also can tell when the exhaust starts putting out black smoke).  Good Luck, TomC

[bluehair]

Well, thanks. I did not know that. I'll get some this week.

[Runcutter]

Tom has a great point, that probably very few folks know.  I was AGM of a 100-bus transit system in the early 1980's.  The previous management team had maintenance blowing out the dry-element air filters with every PM.  That put the dirt, from the outside, to the inside - where it was sucked into the engine.  The whole filter was exposed to the cloud of fine particulates.  We had to major a bunch of 6V71's, way early because of this.  I'd been used to oil bath filters, so that was a learning moment for me. 

To this day, I won't let anyone touch the air filter on my car, or my wife's car --- other than the dealer.  On our previous cars, we used a quick-lube place, and I always watched.  They'd try to blow out the air filter if I didn't intervene.  (We both have new cars now, so dealer service only).   

One of the car-related radio shows used to have a section -- X ways you might be ruining your car without knowing it.  That could be a great topic for this board -- or even an ongoing column for the magazine.  Even after 40 years in the bus business, I'm still learning stuff about bus maintenance on our 4107, now that I'm directly responsible for maintanance (I don't have a Supt. of Maint. working for me any more). 

Arthur