BioDieselNow - Renewable biodiesel fuel

 I just joined the group and hope someone can stopp me from beating my head against the dashboard which I've been doing for the last 4 days. I have a Wayne school bus, 1984, I think, with what is labeled as a GM 8.2L engine (I've  been told it's the same as a Detroit. It runs on diesel, or it did, and WVO, and now it won't run at all. I've put thousands of miles on it, mostly veggie, but my veg supplier ran out for 5 months and I ran on diesel. When I switched over, it lost power. It limped home on diesel, but now it won't run at all. Actually, it will get up to about 500 rpm and chug, then die. I've tried purging air by pumping diesel straight into the injector line, and also by pumping it straight into the return line (which some forum suggested). I now have it set up to pump clean diesel directly into the injector line, but it just won't come to life. I've been through a lot with this bus, but now it's killing me.

I figure it's either air in the injectors (I know it's not sucking air), or clogged injectors. I fear the latter. 

Does anyone know how to determine if it's clogged injectors? I've never had to bleed it like this before, but I suppose that's still a possibility (air).

Thanks for taking the time to read this. I hope I can get it running soon. It's for a science outreach program, and we do at least 3 shows a week (Physics Factory).

John

 I'm about as mechanically inclined as a squirell, maybe less. Your problems brought back memoeries of an uncle that used to steam clean engines, 1967. I wonder if while you are looking around for a solution you might ask about steam cleaning disel engines.

If anyone else has any info it would be greatly apprciated. I wonder if I can still find the gear. He died over ten years ago but I swear the man never threw anything out.

 I'd like to help you, but you might see the BIG BOARD, a risk I'm not sure I can take.

John

I will keep an eye out for steam cleaner, though.

I'd pull the injectors and inspect them, and then I'd do a compression test. 

 Could also be the fuel pump...  Sounds like how my truck was running when the fuel pump went.  It didn't die completely, just didn't push enough fuel.

You can fairly easily pull an injector (or all) and have them "pop" tested at a diesel service facility. It's not a complex test but will tell you if they are popping at the correct pressure. 

How's the injection pump? Are you sure it is giving the injectors enough pressure? My knowledge is weak on this particular diesel engine so don't start taking thing apart until someone else offers a bit more 'first hand' advise for this particular engine. 

Hi,

now this would be the basics, you could probably find more indepth stuff at some diesel forums, some even specializing in 8.2's:

Its runs, but it limps? that being the case you'd first

1.change the fuel filters if you haven't, after that you need to 

2.check the flow from the lift pump (there should be some kind of metering  technic available on the forums, eg: will produce 1/2 liter when cranking for 10 seconds)

3. if the flow seems sufficient you need to check for flow at the injecion pump, again, there may be a metering technic such as  open 1 line (remember, injector pressure can rip your skin open and poison your blood, don't test the lines with injectors attached, check flow with line separated from injector flowing into a container)

If you used the same fuel filters for wvo and diesel, you probably clogged them. Injectors will clog under extreme circumstances, I wouldn't completely rule that out, but I'd go the above (easier routes first) 

I have a pop tester you can use if you're in SE Michigan (that applies to all users btw.) 

Good luck! 

 Thanks very much guys. I appreciate all of your suggestions. Since I'm putting the fuel directly into the injector line now (as a test) the problem can't be in the lift pump or the filters. I've pretty much ruled out sucking air. I'm under the impression that this engine doesn't have an IP, is that right?  I guess my next step is to pull the injectors, something I've never tried and don't know where to begin, but I'll read up on it, and get some advice.

It's great to have the support out there.

John

John, all fuel injection engines, whether they are gas or diesel, require pressure to push fuel through the injectors, so you have to have an injection pump somewhere. Being a diesel engine, I would assume it to be a mechanical pump attached to the engine, but I am not familiar with your particular engine. Follow your fuel lines back from each injector. Where they join together (or close) is where you should find your injection pump. Diesel engines usually put far more pressure through their fuel lines than do their gas engine counterparts. You also have to keep in mind that it is not just about getting fuel through the injectors at the proper pressure, but also at the correct time for combustion. What are you using to pump fuel through the injectors, how much pressure does it produce, and how are you managing to time that delivery?

The first thing you should have to troubleshoot this issue is a factory shop manual for your vehicle/engine. You need to know where the components are, and what the specs are for pressure, timing, etc.

Rob

 Again, thanks for all the advice. 

By eliminating one variable after another, I figured out that the problem was that the return line has an orifice restrictor to keep the right amount of fuel going to the injectors and not just getting pumped back out to the tank. My temporary fix was to put a ball valve on the return line, and set the pressure to about 50 psi. Now I'm back up to almost factory specs (3100 rpm) and plenty of power.

Here are a few things I discovered along the way about my 1989 Detroit 8.2L:

It has no lift pump.

It has no injector pump (the mechanical injectors provide the pressure).

It has a mechanical fuel pump.

Today's question is, does anyone have experience with replacing the return line restriction orifice. The shop manual doesn't offer any advice or photos at all. It may be easy, but right now I just want to use the bus until I get a little more advice. 

Thanks,

John

 I don't know about replacing the return line restriction orifice, but you can try replacing the fuel injector to see if it works.

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