Fuel pump operation ???

[solar7647]

I have been chasing a fuel issue since i rebuild my 3.7L Merc. I believe i have found it but need to verify my understanding of mechanical fuel pumps.

I have the pump removed and noticed that when you manually pump it you get suction and air flow threw the sight tube outlet.........that means the diaphragm is bad right?

My sight tube is all dirty (time to replace) so I never noticed fuel coming up, but the engine acts like its flooding out, idles ok but when you give it throttle is just bogs and dies.

Done so far to find issue:
checked and reset timing 4 BDTC, valves all good by compression test, carb swap, new plugs, wire, electronic ignition, clean gas. Carb swap was with same kind of carb (Q-jet not new but functions)

 

[Blk-n-Blu]

Re: Fuel pump operation ???

Might be time to take a look at the diagnostics that Don S has provided in the "Adults Only" stickey, Maybe they will help. Click here:
http://forums.iboats.com/showthread.php?t=283269

 

[jtmarten]

Re: Fuel pump operation ???

Plug wires in corect order?
4* base timing seems really low. If your fuel pump is failing, you may not have enough fuel in the bowl(s), so you create a lean condition when opening the throttle and she dies. When she dies, look into the carb venturi, pump the throttle and see if the accel pump is still pushing gas.

 

[Bt Doctur]

Re: Fuel pump operation ???

the sight tube fitting will have a pulse of air. Your raising and lowering the diaphram inside.
the fuel transfer valves are above it.Thats where you would check for suction and pressure. Another test is to hook up a vac. gauge to the fuel line where it enters the pump.A hi vac. reading suggests a restriction. might even be the anti-syphon valve at the tank fitting.

 

[solar7647]

Re: Fuel pump operation ???

Thanks I will check out the thread, didnt see that one.

4* is what it should be set at according to Manuel.


I have done a load of test to try and find the problem and everything keeps pointing me to fuel is.

It will run fine on muffs and at ideal. But when its under load, it has no power and then falls on its face and dies, with a backfire through the carb.

I first thought valve but did a compression test and get a very repeatable 150, 145,145,145. With out popping the front cover off every thing seems to say valve timing is good. I didnt set the timing chain it was pre-set from the machine shop that I bought the long block from.

I installed roller rockers and thought perhaps that was the issue, removed and did same thing with stock rockers. They are also all the same as far as valve stem clearance when lifter fully collapsed.

Then moved to spark, new plugs and wires.......same thing. Upgraded to elec. ignition from points and same thing.

Moved to the carb and found leak so it is getting rebuilt at shop. While it is in the shop I got a different one and it ran smoother but still same thing under load.

So now i am at the fuel pump to rule it out as the cause.

 

[achris]

Re: Fuel pump operation ???

Throw the old mechanical pump in the trash, buy an electric pump, wire it up with all the right safety things (oil pressure switch) and have fun for years....

 

[Don S]

Re: Fuel pump operation ???

Throw the old mechanical pump in the trash, buy an electric pump, wire it up with all the right safety things (oil pressure switch) and have fun for years....

Why do that ?????? The mechanical pumps outlast the electrical pumps.

 

[achris]

Re: Fuel pump operation ???

Why do that ?????? The mechanical pumps outlast the electrical pumps.

If the mechanical fuel pump is pushing fuel up the sight tube, then it has a broken diaphragm. Great opportunity to replace with a more reliable option.

 

[solar7647]

Re: Fuel pump operation ???

Well I think I have just ruled the fuel pump out. Inspection of diaphragm came up with nill.

I cant see if fuel is coming up the sight tube beacuse its to dirty, I need to replace it.

I did notice that there was 0 fuel in the line from tank to pump, so i will have to grab a small portable tank and run it to the pump to rule out anything being wrong with the tank and components.

I am open to any other suggestions on what the issue could be...........

It will run on muffs at idle fine and in the water at idle fine, but when under load it has no power and falls on its face with a backfires threw the carb several times and then dies.

 

[solar7647]

Re: Fuel pump operation ???

Well i have to go to work so I will pick up the conversation there in about an hour.

Talk amongst your selves......

Hears a topic.......

Fixing Solars boat!..

 

[solar7647]

Re: Fuel pump operation ???

So any ideas? I really need to get this thing going.....the kids and wife are going to riot soon!

 

[achris]

Re: Fuel pump operation ???

Cracked pickup in the tank? Small crack that doesn't leak air under small suction, but opens up when the engine demands higher volume... Just putting it out there....

 

[patrick1010]

Re: Fuel pump operation ???

timings not advancing. Does it fall flat on its face and then back fire through the carb? does it rev up under no load? Can you check fuel pres.?

 

[solar7647]

Re: Fuel pump operation ???

Cracked pickup in the tank? Small crack that doesn't leak air under small suction, but opens up when the engine demands higher volume... Just putting it out there....

Tomorrow, I am going to re-install the pump and hook it up to a small tank to see try and norrow issue to tank or rule it out.

 

[solar7647]

Re: Fuel pump operation ???

timings not advancing. Does it fall flat on its face and then back fire through the carb? does it rev up under no load? Can you check fuel pres.?

I need to get a fuel pressure gauge yet, but plan on doing in the next few days so I can check.

Yes I can rev under no load, does pretty good but seem to struggle a little.

Hears the step by step:

Starts on first turn of the key and keeps ok idle, its a little surgy but constant ( if that makes sence)

Go just into gear, <1000rpm, same thing as idle

Add throttle, it wil come up to about 1300-1500 RPM and then falls on its face and back fires threw carb but not die.

Even more trottle and it will continue to come up fall on its face and backfire threw carb, but not die

Hit WOT and there is little to no pick up in RPM falls on its face backfires threw carb and dies. Then takes some cranking to get started.

Bring back down to idle keeps constant idle with surg

This all makes me believe that I have a lean condition being caused by something.

 

[patrick1010]

Re: Fuel pump operation ???

I would say lean condition too. Let us know pressures when you get them

 

[solar7647]

Re: Fuel pump operation ???

Well, I found the issue, and I am not happy! The cam lobe for #1 intake, #3 exhust and #4 intake.........All BAD and so are the lifters! I was pretty much running on 2 cylinders. I contacted the machine shop that did the work on the engine and they claim its not warrenty covered because its cause is lack of zinc in the engine oil! yes that can cause premature failer in flat tap cam systems but not that fast! I havent even run the thing under load.

I did the cam break in 20 min at 2000rpm.......>!

Since I kept such good record of the rebuild I looked through the photos and noticed there was no molly lube or any lube of any knid on the cam lobes that should have been applied during installation........I called the shop to have them explain and after a bunch of run around I gave up! Will just have to buy a new cam....o well at least I will know 100% that its installed and lubed right! Plus I can do other things to the engine that would have voided the warrenty. I just dont have the time or the energy to go back and forth with them, just going to eat it, fix it and go.

I know I should have checked, but I put faith in the fact that the shop diid it right. My mistake! I hear by retract every good coment I ever said concerning that shop!


Good lobe on the left bad on the right

Bad lifter

 

[fat fanny]

Re: Fuel pump operation ???

Solar what a drag for you and yours after all that great hard work but you will prevail and make sure you post something in your local news paper about that shop. I work in a machine shop and we build some of the biggest machines in the world and we gaurantee every part on them period!!!!!!!! especially after that long in your case. Do what you have too I know only to well you have to eat it sometimes to get what you want. Good luck and keep on keepin on.

 

[solar7647]

Re: Fuel pump operation ???

Solar what a drag for you and yours after all that great hard work but you will prevail and make sure you post something in your local news paper about that shop. I work in a machine shop and we build some of the biggest machines in the world and we gaurantee every part on them period!!!!!!!! especially after that long in your case. Do what you have too I know only to well you have to eat it sometimes to get what you want. Good luck and keep on keepin on.

I would love to do that but the machine shop is out of state! None around me could do it and the Mich. Motors in steerling heights wanted over 4K ! Thanks for the thoughts, i am trying to get the parts by Friday so I can rap it up this weekend.

 

[Eric 3.7LX Alpha 1]

Re: Fuel pump operation ???

What else can you say but INCREDIBLE! Man that sucks, after all the work. N ya gotta hope that the metal that was removed from the cam and lifters won't get into the bearings. I did have a friend with a SBC 350 in a Chevelle wipe out a cam and lifters like that, he changed the oil a few times after the 1st start up and the thing held together many years.

Did you prime the oil pump with a drill before start up? We've done that on new engines in cars, Summit racing sells oil pump primers for SBC. You have to remove the distributor to do it but you can let it prime for like 15 minutes and get great oil all thru the engine before firing it off. Had to use a 1/2" drill to have the power. Can check the oil psi gauge to confirm its pumping oil.

I've used a distributor without the drive gear installed and top cut off. Bolted in and connected to the drill to drive the pump at the bottom. Sure you not gonna be able to get one for a 3.7, maybe improvise one?
Just an idea.

Good Luck with it!!!!