Mech. fuel pump failure modes?

Guys, I have a frustrating problem with my fuel system.. and before I start ripping stuff apart and/ or throwing new parts at it, I would be gratefull for some advice...

Here's the deal, I have a megasquirt EFI system fed from a high pressure pump, which is in turn fed from a the mechanical pump, one for pressure, one for suction from the tank.

Untill recently, the return from the pressure regulator was just fed back between the mech and electrical pump.

After installing a big radiator and electric fans, the under bonnet tempperature increased as there was now no mechanical fan running constantly. This caused idel and re-start problems when hot due to the recirculating fuel boiling.

To remediate this, I did a proper return line to the tank, and that problem was solved.

Some days ago, the engine went lean sputtered and stopped. Gauge on regulator showed low pressure.

Lat the car stand for a while and tried starting ut until battery died. Got a buddy and did several attempts at jump starting. pressure increased very slowly. and once we got it to start, drove it straight back home keeping the revs up on the assumption that the electric pump was failing and needed all the help it could get from the mech. pump. Barely made it back, the engine dying as I rolled in to the drive-way.

Changed electric pump, checked everything from the electic pump back through the return line, fine. Pressurte was slow to build, I assumed this was due to the system needing some priming.

today, car started just fine, pressure where it shoudl be, went for a drive today, and as soon as the engine got warmed up , same thing happened.

This time the car died just before I got back home. Walked back to the hous, got a rag and some icecubes and wrapped arround the mech pump.

After the pump was cooled down, the car started after a lot of cranking and drove the last bit. left the engine idling and checked the fuel pressure. A tad below where it should have been, and not 100% stable.

Now, can a meechanical fuel pump fail partially with reduced volume and/ or deterioration of volume when hot, or do they just plain fail?

I assume the system design is OK, as I didn't get this problem straight away after re-designing with the new return line system.

Just to elliminate the mech. pump as a possible issue alltogether, I could allways install an electric suction pump next to the fuel tank.

But this is a bit more involved than just replacing a failed mechanical pump.. if its (partial) failure is actually the case..

So, how have you seen mechanical pumps fail???

Sounds like the increased under hood temperatures are causing vapor lock.

Please detail your "proper return line to the tank". If the system isn't vented properly...
Starting after cooling the pump may have been just coinsidence.

Iagree, it sounds like vapor lock.. the only doubt I have about that, is that this didn't appear on the first drives I did after I modified to the return line system.. and the drive i had today was substantially shorter, i.e. it seems like something happened during the previous drive when this suddenly happened..

It is certainly not like the occasional vapour locks I had with the "closed loop" regulator return set up...

Good point, conincident events may not allways be related!

Well, I re-did the original vapour return line with 8mm ID tubing hooked it up to one of the fuel tank "vapour condenser" inlets, and hooked it up to the regulator bleed-off with a piece of flexible fuel line. At idle before driving off today, I pinched that flexible hose with my fingers, and I could both feel and hear the fuel rushing through the "pinch" so that seems to be flowing quite freely.

The fuel cap is fully vented and there are never any signs of under-or over-pressure in the tank.

The original vapor return dumps high in the tank because it was only vapor. I really just dont know what a solid stream of fuel entering there would do to the system. I suppose if the tank was more than half full that wouldn't matter.
so now I've brought the fuel level into this puzzle.

Hmmm, well, if the fuel enters low or high.. it still enters...

Allso, read various articles where some people state that "the fuel gradually heats up" due to the continous recirculation through the engine bay, thus eventually causing boiling and vapour locks.. put my hand on the fuel tank, normal temperature... as expected.

I decided to go for an electric feed-pump, or rather, two feed-pomps in parallel to ensure that I got a feed rate that was higher than that of the High-pressure pump.

The Local auto-warehouse had some units that wasn't too expensive.

After installation and some priming to get the iar out of the system, the pressure gauge went bang to the set pressure instantly, and the car started fine.

Took it for a test drive (only a relatively short one, incase of trouble), and everything was OK!

The bad thing is that these pumps are very noisy, making a pronounced ticking sound. In all likelyhood, they will be replaced sometime in the future with a rotor or turbine pump that is quieter.

But at least I now have the car on the road.

Allthough this modification has positively elliminated any possible issues with using the mechanical pump for feeding, I did discover something that may well have been the root cause of the problems, The short rubber hose between the tank pickup and the fuel line.

It was very badly deteriorated at one end, to the point where I think it more than likely that it allowed air to be drawn in.

OK, perhaps I should have checked that out first, but at least I now have a feed pump set up which work and should allso work for a hoped for future HEMI III conversion.

And finally, thanks a lot for all innput and comments!

Damn.

Well, here's the latest discovery..

As mentioned, the new electric feed-pumps made a terrible noise to the point where it sounded like the car was borken or something...

With the negine idling, the old mechanical pump disconnected but running, it made a very pronounced "wuhu-wuhu-wuhu" sort of sound. I put my thumb against the outlet, the sound disappeared and there was pressure against my thumb.. did the same on the inlet to find the sound disappearing again and positive suction building up. Hmmm

Before I changed to the electric pumps, that sound was there allthough not as pronounced as with the pump completely disconnected...

Could that have been an indication that the mechanical pump was in deed drawing air through that degraded hose between the tank and the fuel-line?

Disconnected the electric feed-pumps, put in a fresh piece of hose and re-connected the mecanical pump.

Started the engine, fuelpressure rose quickly, and there was no "Wuhu-wuhu" noise from the pump.

Did a relatively short test runn and got back home allright, still no noise from the pump.

I think I got to the root cause of the problem, and those dreadfuuly noisy electric feed-pumps are going out again!

I've been thinging about replying again. I wasn't going to, but I changed my mind.

Let me first say this. I'm not bashing what you're doing here. Lord knows I don't know what all you have available to you in Norway......but man, those fuel pumps you're using are JUNK. They are almost not good enough for a riding lawnmower.

Also, you've got WAY too much rubber hose in that system. That's dangerous.....as you've proven by showing that cracked up rotten *** hose in that picture. What I would is try to get some fuel injection hose. That won't rot out as bad.

Also too, it's best to try to keep rubber hose to a minimum in the system. Over here, NHRA mandates only 12" of rubber hose in the whole system. Even if yall don't have rules on the tracks like that over there, it's still a good idea.

If you want to stick with an electric pump, Summit makes some nice ones that mirror the Holley black and red pumps for a lot less money. Here's a link to the Summit pumps. They work good. I have used them before.

http://www.summitracing.com/search/...ric-External/Brand/Summit-Racing/?Ns=Rank|Asc

If the noise bothers you, get an old tire and cut a section of the sidewall out big enough to go between the frame rail and the pump bracket. That will insulate noise real good and last a long time.

Like I said....I ain't bashing. I just want you to stay safe. Gasoline ain't nothin to play around with. We don't need a burnt up Norway friend.

i wasnt going to comment myself, but i couldnt agree with SS more. that is a serious spaghetti nightmare and is a fire waiting to happen. i mean this in the nicest of context. if you must have an electric pump, get yourself ONE good 5-7 psi fuel pump and mount it to the frame rail with a regulator following right behind it. use as much hard line as possible. you can even run it through your mechanical pump . use a quality fuel injection rubber line. i run a 15 gallon fuel cell on the street and my set up goes like this

fuel cell~inline filter~a big carter 5-7 psi electric pump mounted below the cell on the frame rail with rubber isolators~5-7 psi regulator set at 5.5 psi~hard line~mechanical pump~inline filter~fuel pressure gauge~carb. im not saying this is ideal, but i have less than 15 inches of rubber line in the whole system. i have a steady 5.5 psi of fuel pressure and if either pump fails, i have a backup.
besides sucking air , you will develop a leak somewhere and if decides to land inside the brake drum you could have major issues..
you really should consider taking all that mess out and reworking it before something bad happens.....just lookin out for ya

the brake line looks like its copper it maybe the pic . copper brake lines are illegal here and they would string you up by the balls if caught using them all tho i have used them many years ago without fault. good luck on your fix.

looking at it again and it maybe the return line and not a brake line my mistake

Oh and I won't just come in here and hack your stuff up and leave..lol....if you need someone to help you with finding some injection hose, I will be more than glad to. Long as you pay for it, I will find the cheapest way to get it to you and ship it to you. Just let me know. Shoot me a PM if I can help.

StrokerScamp said:

Damn.

Click to expand...

correct.