AAARRRGGGGHHHHH!!! MFI frustration!

KevinG · KevinG's Garage

After 380 days I thought my baby was going to roar once again. No such luck. Traced out and fixed a ground problem that was keeping the sparks from sparking, but found that it's hard to start a car without gas.

Fuel filter - new (check)
Fuel pressure - check
Fuel to MFI Pump intake - check
Disconnected injector hard line from #4 injector - dry!
Cranked motor over a few times, just a drip or two came out, no pressure
Cranked motor and watched MFI belt and pulley go roundy-round.

MFI pump was removed and oil lines capped for duration of rebuild, nothing else was done. Pulley rotated freely when reinstalled.

At this point, the only thing I can think of is the plunger or tappets have been 'laquered' in place due to long term storage without cleaning (rebuild was not supposed to be a year+).

I would really like to hear from some of the MFI experts on the board before I yank the pump and tear into it needlessly. BTW - the pump was rebuilt by PFI about 5,000 miles ago.

Any and all opinions very welcome

addictionMS · addictionMS's Garage

not a MFI expert, but two things I would try, make sure everything is soaked in gas, and let time have a crack at fixing it, loosening everything up, if that did not work I would tap it on the side a few times to help it along.

Again never had MFI but this does work for EFI injectors sometimes

Jim

304065 · 03-23-2005, 09:31 AM

Do you have the lines routed correctly from the electric pump to the fuel filter console, to the MFI pump, back to the filter console, and into the return line back to the tank? The factory diagram is WRONG, Grady posted a corrected diagram here.

The hose to the pump comes out of the bottom of the silver can filter. When you remove the banjo fitting on the MFI pump, do you have fuel? Is that banjo fitting connected to the INLET opening on the pump?

You could remove the hardline from the #4 cylinder on the pump and pour in some B-12, if you thought it had gummed. But it's more likely a fuel delivery problem to the MFI pump itself, not a gumming-up, IMHO.

How about some pictures of how you routed everything?

304065 · 03-23-2005, 09:38 AM

Braided Fuel Hose for a 72T MFI

BURN-BROS · 03-23-2005, 09:48 AM

The way to check for the plungers to be laqered is to remove th dust cap for the rack. manually move the throttle linkage and look for movement of the rack. If you cannot see you can use a dial indicator to measure movement of the rack. If the rack has no movement you have stuck plungers. Do not attempt to force the rack or internal damage could result.

KevinG · KevinG's Garage

Thanks, John - that was some thread!

My MFI hoses are routed as shown in Grady's picture. Although not in the picture, I have the MFI Pump inlet as the one on the right side (inside) of the pump, immediately above the oil lines. The outlet would then be the fitting next to the throttle body assembly on the drivers side.

I disconnected the inlet hose (the one coming from the bottom of the filter) at the pump fitting (above the oil lines) and stuck it into an empty 12oz beer bottle (lots of those lying around for some reason). A few seconds with the key in the on position nearly filled it.

Eagledriver · 03-23-2005, 11:27 AM

I went through this on my car last year. There was nothing wrong. It takes along time of cranking to get enought gas all the way through the lines and to push all the air out. I'd say it took at least 2 full min. of cranking to start. The cranking doesn't need to be done all at once. I did it in 15-20 second intervals.

The MFI pump puts out very small amounts of fuel when turning over. Think about how little fuel your engine burns at idle. The fact that you had a couple of drops out of the number 4 line tells me it's working as expected.

-Andy

Tspringer · 03-23-2005, 01:33 PM

Make sure the return line from the pump to the fuel tank is not blocked. If so, you will get no flow. Junk in the bottom of your tank can cause this.

Bobboloo · Bobboloo's Garage

I know I'm a bit late to this thread but I just wanted to suggest that you make sure that the steel lines from the injection pump to the injectors are torqued properly. If they aren't you loose pressure and then the injector will not open to spray fuel.

Being that everything was fine when you took the induction off I would check this before digging into the pump guessing that it might have laquered up.

I did a rebuild on a 2.4T and set the pump aside longer than you did and it stumbled a little at 3k when I first ran the motor but it evened out after a few days.

Shuie · 03-25-2005, 03:17 AM

Im not an MFI expert, but have yuo gone through CMA yet?

Tyson Schmidt · 03-25-2005, 07:07 AM

Andy is right on this one. You need to prime the system. It takes a long time to fill the lines to the injectors.

Here's what I do. Remove the belt from the pump. Use another belt to put over the pump drive sprocket, and use an electric drill to spin the pump. Make sure the key is on so the fuel supply pump is running. Then reconnect the belt. (correctly timed, of course)

Or sometimes I'm lazy, and use carb cleaner sprayed down the stacks while someone starts the car for me, and keep it running with the spray until it self-primes.

Or you could run a jumper wire to the cold start squirter to inject fuel to keep it running until it primes.

KevinG · KevinG's Garage

Thanks for the ideas, guys.

I tried 5 minutes of cranking last night without success. I already know I've got adequate fuel and pressure to the pump, so I will check that the flow from the pump to the filter and from the filter to the tank are ok as well. That being said, wouldn't the pressure to the pump still allow for fuel to the injectors despite a possible blockage in the post-pump lines? I thought the loop was just to insure adequate fuel supply under various throttle conditions.

I like the other ideas for priming the system as well, and will try them before moving the pump to a bench. Removing the pump with the engine in the car ain't my idea of a good time. I will also try shooting carb cleaner through the lines themselves to make sure no critters got in them while they were sitting, even though getting all six blocked would be stretching things a bit.

Grady Clay · 03-26-2005, 11:18 AM

Kevin,

This is one reason I like the ’69-’71 front cover to the pump. It has an enrichment solenoid that pushes the rack full rich. This allows you to not use the cold start nozzles that many think are a fire hazard. It also allows easy priming of the system.

There was a thread a few weeks ago about a similar issue. The pump pistons were stuck after an engine rebuild. A few days of soaking and turning over solved the problem.

Best,
Grady