Good MFI test procedure ?

Tspringer · 04-15-2003, 04:11 PM

Still trying to figure out how on earth my 2.7RS MFI engine is puking fuel into the oil in large quantities.

I starting to really suspect a bad injector. I does not appear the pump is the problem (see other thread on no oil return lines). Also the car runs great and does not throw black smoke so I dont suspect its a massively rich running condition. That leaves a bad injector?

Here is my thought process on this:

The fuel system too, through and out the pump stays under some pressure as delivered by the fuel pump. This is so there is always fuel in the system and pressure does not have to build every time the car is started.

This small amount of static fuel pressure is not enough to open a properly operating injector. However, an injector that has some trash in it or is otherwise "screwed up" may allow raw fuel to flow through after engine shutdown. It may allow all of the fuel in the fuel lines and injection pump to dump into an intake port until there is no longer any pressure in the system at all.

If this assumption is feasible.... and thats an "IF".... then hows this to test for the problem:

I install a cheap fuel pressure guage in-line on the fuel input line to the MFI pump. If after shutdown the pressure in the system remains constant or bleeds down very slowly then that would point to no injector problem. If however the pressure immediatly bleeds down quickly.... then fuel is leaking out somewhere and I have a bad injector.

I could attach the pressure guage to the fuel return line as well and test from there.

Does this sound like good thinking... or am I whacked in the head?

Terry

Early_S_Man · 04-15-2003, 04:31 PM

Terry,

Whacked maybe ... or just dazed by the sight of no oil lines to the pump ...

The amount of fuel available to the injectors is strictly controlled by each piston per injector/cylinder in the pump ... and basically irrelevant to the pressure level in the gallery. So, I don't see how a temporary pressure gauge would tell you anything but the health of your electric fuel pump, filter assembly, hoses, and hard lines.

If you want to test injection pump and injectors at the same time ... I suggest removing the pump and injectors from the engine ... and move pump, then reassemble hard lines and injectors on a bench in the 'butterfly' configuration with injectors hanging in mid-air. Rig temporary supply and return fuel lines to car ... and stick short hoses over the injector tips ... draining into six baby food jars (or similar) ...

After the 'test rig' is bled of any air and six timed squirts are being generated ... dump all six containers so that a volume comparison can be made at the six injectors after 20 - 30 revolutions of turning over the injection pump by hand. If all six collection containers don't measure within a milliliter or so ... you will probably need to talk to Gus again. Good luck!

hbrand · hbrand's Garage

What kind of starting enrichment does your engine have? Mine has 6 little plastic jets and they squirt fuel direct into the stacks. Maybe they leak somehow when the engine is not running and so putting fuel into the intake and from there into the engine.
Thanks harold

Tspringer · 04-15-2003, 05:51 PM

Harold, my cold start solinoid is hard wired with a button under the dash. It routes fuel to the air cleaner assembly and an intake stack as per the stock setup. I disconnected the fuel hose going to the air cleaner and attached it to a catch can. After driving around a good bit there was no fuel in it. Thus, I dont think my problem is related to the cold start.

Terry

hbrand · hbrand's Garage

Have you ever solved the gas in oil problem??
Thanks, harold

304065 · 05-27-2003, 03:11 PM

Ahh, Harold's question is related to whether you have a cold-start solenoid on the pump itself, '69-style! If locked open could be throwing a super-rich mixture. Your pump does have only one solenoid, the over-run, right?

Terry, I think that if you were to install a pressure gauge in the lines, it would read between 1 and 2 bar all the time, and then if you lost pressure, e.g. the residual pressure in the supply line bypassed the cylinders in the pump and bypassed a piece of crud in the injector, dumping raw gas into the cylinder, you would notice the following symptoms:

1) it would take some time for fuel to fill the pump and the filter plenum, delaying your starting; and

2) on startup you would get a huge puff of smoke from the exhaust, possibly even a backfire as the raw gas got dumped into the muffler.

If you really want to test for #1, run the car, unplug the fuel pump at the two-pin connector back by the filter console, and see if it doesn't start. That would tell you whether you have lost pressure.

Warren is (as ever) spot on, the only way to verify the injectors are ok is to test them or replace them with known good ones.

I didn't see your other thread but if I understand it correctly you may have disconnected the oil lines from the pump?

hbrand · hbrand's Garage

Have you ever compared all 6 spark plugs?? They should all be exactly the same color and condition. If they are, there is no problem in the top end or injection. Also, are you sure that your engine is running on all 6 cylinders? The 2.7RS engine is so strong, that even running on 5 cylinder the car moves pretty good.

Anyway, the gas can only get into the engine through the injectors and is burned off OR NOT.
thanks, harold

Tspringer · 05-27-2003, 05:12 PM

Problem not solved. mostly due to time constraints... I have a 308GTB Im getting a bunch of stuff done on to sell it. Thats been my priority right now.

I did use the Gunson Gas tester to do CO tests. They showed at idle it averaged about 2.9% but running at a steady 2200rpm on the hand throttle it was averaging about 12%. Too rich off idle clearly. Im betting this is the problem and I plan to adjust this ASAP. I will probably remove the injectors and send them off for testing since I plan on really taking the engine bay apart and detailing it.

Eagledriver · 05-27-2003, 05:26 PM

I used to think that fuel in the oil was from running rich. Now I've seen it mentioned so many times with MFI and experienced it with my own MFI cars that I think it is from the pump itself. I think that as the pump wears the plungers start to have fuel "blowby" just like worn pistons in a cylinder. The fuel then is in the body of the pump and gets into the oil that lubricates the pump.

I'd be very suprised if you don't have your oil lines hooked up because I would think that the pump would be destroyed in short order without pressurized oil to it's working parts.

I've decided that since my current MFI car does this only a little I'll just change the oil more often. Once it gets bad enough you'll have to have the pump rebuilt.

Todd Simpson · 05-27-2003, 05:34 PM

The lack of oil lines is discussed here...

MFI with no oil return ?!?!?!?!

Eagledriver · 05-27-2003, 06:05 PM

Thanks Tod,

I'm amazed at how much I learn here. I've never seen a pump not hooked up to the oil system before. I guess the factory hooked it up just to make sure the pump never ran out of oil.