fuel pump pressure for MFI

[Pferg]

I have been trying to adjust the MFI on my 73T after having it apart to unstick on of the pump pistons. I have the blue book and the tech notes and have been checking adjusting at much as I can do without a CO meter. My goal is to drive it to a shop, not tow it, so it can be adjusted by a pro.
Currently the car is still not drivable, it sounds ok, revs to redline and idles ok; some intake popping when hot but no serious backfiring through muffler or intake.
The problem is lack of power, it accelerates in first then dies in second, no acceleration there, I thought I could do better than this by sight and sound. I checked the fuel pump pressure into the MFI and it is 12 psi regardless of engine speed. I know the pump out should be 15-17 psi at the pump but I 'm not sure how critical this is . I was expecting the fuel pressure to drop on demand thus explaining my lack of power but no dice. Its the same at all speeds. I am speculating that the line and filter may account for a few psi loss from the pump. Any comments on the pump pressure. Is it a reasonable expectation to get it drivable without a CO meter ?

[304065]

Pferg,

I can point you in the right direction here, only insofar as I've been re-engineering the fuel system on my '71 and have been advised that the pump's output should be between 1 and 2 bar at all times, measured in the loop from pump to filter console.

Roland Kunz is the maestro here; he gave me some good advice on fuel pressure requirements in the following thread.

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=61592&highlight=mfi+fuel+pressure

And let's not forget Warren Hall, who gave similarly good advice in this thread:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=6546&highlight=mfi+fuel+pressure

The above would be relevant if it is, in fact, low fuel pressure that is causing your problems. But if you've had the MFI pump apart due to a stuck piston, I suspect that your problems could lie deeper than that.

It's interesting that you say it accelerates in first and dies in second. If it's pulling hard to the redline in first then I wouldn't think it would be ignition advance-- and the engine doesn't know what gear it's in, right? So do you think that you are getting sufficient pressure to the MFI pump and plenum inside the filter console at idle, then you accelerate in first, the level in the filter console and lines to the pump drops, and then you shift into second and the pump begins to run dry, cutting the power output?

I would say, if you have it isolated to the fuel system, to change the pump and see if it helps. But that's a $300 bet.

What do the plugs look like?

[Early_S_Man]

A few questions ...

1. Have you checked the pump output volume? It is supposed to be 900cc - 1000 cc in 30 seconds. If the quantity is low, be sure to drain the fuel tank and check the fine bronze screen in the fuel tank ... BEFORE ordering a new pump! It wouldn't hurt to blow out the fuel lines in the tunnel, either. If rust is found, the tank needs to be steam cleaned and sealed, and the steel lines need to be replaced.

2. Have you checked the ignition advance curve from idle to 6000 rpm? All of the pertinent data for your car from the factory spec book and service manual is posted in the following thread about distributor maintenance:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=5432&highlight=distributor+lube

3. Before you put your injection pump back on the engine, did you assemble pump, lines, and injectors in the 3-D 'butterfly'[ configuration ... on the bench, fill pump with fuel, and test injector spray pattern and fuel quantity injected per cylinder for 30 - 50 revolutions of the drive gear? If rust or corrosion caused a plunger to sieze, you may need to send the pump off to be rebuilt!

[Pferg]

Thanks for the reply , I don't think I have an ignition problem . It all new and the advance moves smoothly to 30 degrees btdc.
I think the fuel pump is ok because it seems to meet the increased demand without dropping pressure. And thats why I put this mesage up as I was looking for some yea's or ney's on that. I'm not up for replacing the pump prematurely.
As far as the MFI goes. I could have done something wrong, I pulled the cam cleaned up the stuck piston , set the preload on the pump torsion springs and reassembled it using the Bosch overhaul manual. The rack works smoothly now and all of the cylinders are getting fuel. When I richen the mid range screw the exhaust gets blacker when I lean it I lose my idle and it pops. I guess I'm just surprised I need a CO measurement to get it to be driveable.
I will check the plugs to see if any are fouled.

Answer to second reply
I havent checked the pump volume. I will when I get a helper .

The tank was removed and cleaned this winter. I shloshed it with muriatic acid. took out lots of rust. I cleaned the screen but did not replace it. Tank has been full of gas since. Fuel filter is new.
I'll get a sample when I do the volume check.

I didn't look check a curve, only that it advanced to 30 degrees at 6K.
I didn't bench test the unit. The pump (car) was sitting for a few years before I started it and noticed cyl 6 wasn't firing. In hind sight I may have gotten away with freeing the piston without dissambly since it freed up when I put a heat gun on it. It seemed like the torsion spring for #6 lost its preload somehow as the rack would spring back only with #6 unclamped. Once I freed the piston and set the spring preload the rack returned fine with all six pumps clamped up.
I did have the injectors flowed and they were all ok. The car and pump have 80K miles if thats relavent. If the MFI pump is it I'LL send it off I'd just like eliminate the other items before shelling out $$$.

[Pferg]

I did the volume check. I got 1100ml in 30 sec from the line pulled at the MFI pump. Doesn't sound like its the fuel pump. Is my next step to get a CO meter? Anybody in the Seattle area know where to rent one?

[Jandrews]

Hello,

I thought I would go ahead and comment on this thread after my experiences this morning with my MFI setup.

I recently had my pump rebuilt by Pacific Fuel Injection, for a very similar problem as you describe. In my case however, the number three MFI plunger tappet had broken and a piece lodged in between the tappet and it's wall. Bottom line...siezed plunger.

Anyway, got it back from PCI and re-installed. Gus at Pacific had it calibrated a little lean I believe, since it was stumbling, hesitating and backfiring through BOTH the exhaust and the intake stacks. Not sure which way to go, I went two clicks to the left on the main rack (richer), and she straightened right out.

Based on my experiences, my motor likes to run rich, rich, rich. Also based on the symptoms you describe, I would try going WAY rich to see if it fixes your problem. You can always back it off if you need to. When I say WAY rich, I mean up to one revolution or twelve full clicks. You may not need to go that far, but I have found that it will run on both ends of that spectrum, just very poorly on one end and just about right on the other. I was very surprised to find that I was getting backfires through the exhaust while running considerably too lean. This caused me some confusion, but in the end, it was rich, rich, rich that got mine just about right.

I know this goes against all conventional wisdom and factory instruction, just trying to pass on what I have found in the hopes that you can get it driveable.

Hope this helps...


JA

[Pferg]

thanks for the suggestion John. I think that is the direction I need to go. Road testing is a bit scary at this point because I don't want to be a speed bump for some SUV. When I first put the MFI pump back on it was so rich the engine wouldn't accelerate above 3k unloaded. I have continued to lean it down so it will accelerate crisply to 6k. Maybe I've gone too far. I'm putting a new muffler on today to keep the peace with the neighbors. I have a lead on a CO meter , hopefully that will pan out.