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Intermittent Mechanical Fuel Pump Failure

engine

Best Answer SminkyBazzA , 04 July 2019 - 10:23 PM

Because the problem started after the fuel pump was removed to replace the seals, we figured that's got to the be problem, however unlikely. We do the jam jar test again, but this time with some prolonged and aggressive revving - suddenly the pump stops pumping at all and doesn't start working again until the engine is stopped.
 
A lightbulb moment occurs, and the pump removed to check something: Result!
 
Apparently the pump is a PITA to reattach in-situ. For those that don't know (as I didn't) it is attached to the engine with two bolts, and has an arm that goes inside the engine block and rides against a cam which actuates the pump. In this case after replacing the seal and getting one bolt attached, the pump was rotated into position slightly to get the second bolt aligned and screwed in. 
 
Without realising it, when it was rotated the fuel pump arm was not properly positioned against the cam face, but was instead pushed against the edge or side of the cam, bending it slightly to one side.
 
Somehow, at lower revs and with gentle driving, there was enough friction/pressure for the side of the cam to operate the pump slightly, but not at the full travel of the arm - I was getting some but not all of the fuel the engine might need. After the engine reached a certain speed or was aggressively driven, the arm would slip completely and not regain traction until the camshaft slowed down sufficiently. Me keeping the revs up as I was changing down the gears didn't let this happen so stalling out was guaranteed. The more often the cam slipped, the more likely it was to again (hence the problem starting to occur at lower speeds).
 
Here's some pictures we took before straightening the arm and carefully reattaching. To test this (officer) I've been driving at all speeds/styles since then without issue.
 
I hope this helps someone else in future, no-one I've spoken to had ever heard of this happening.

 

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#1 SminkyBazzA

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Posted 04 July 2019 - 10:20 PM

(This is a problem I ran into that took my mechanic and I a little while to figure out, and which despite reading a lot of great threads here I wasn't able to find a solution to. So this is a record for anyone who happens to run into the same problem in future, with the solution as a reply below. I've tried to cram it with as many key phrases I searched with before, so it's a bit wordy, sorry. Also, I've probably got the order of events slightly wrong.)
 
I've got a 1993 Rio, with a HIF38 carb, electronic distributor. After having a frontend suspension rebuild, new clutch kit, and some oil seals replaced (including fuel pump seal), the car ran fine for several weeks of usage around town.
 
Then I went on a longer trip into Wales, and soon after getting up to 70mph on the motorway, the engine started stuttering/misfiring, and rapidly lost power. I shifted down through the gears, keeping the revs up, but no power so quickly pulled over, before stalling out.
 
Checked the new-ish fuel filter between pump and carb, no scary debris, some fuel present.
 
Temperature was fine, was able to restart and idle fine, revving high in neutral also seemed fine. Yet trying to pull away rapidly reproduced the problem at low speed. Waited for recovery, everything checked over. AA guy backs off the fuel mix a quarter turn. All seems fine and car behaves itself at a steady 60mph, before getting stuck in traffic and crawling for a few miles - despite rising engine temp, everything is still fine. 
 
Carry on with the journey, but shortly after run into the same problem on a long climbing dual carriageway in Wales. Abandon the trip, get towed home.
 
At this point I thought it could be ignition related, or over/under-fueling (though no signs of fuel overflowing the carb, and the float had been replaced recently). Replaced the coil and HT leads, checked all the LT cabling and voltages too, nothing unusual found. 
 
Went out again on the same route, same problem on the same hill climb. Bit more patient this time, so sit with the engine off for a while, then set off again keeping the speed down. Get home no problems.
 
Research suggests fuel vapourisation caused by a missing spacer, but says mechanical fuel pumps themselves either work or they don't. 
 
My mechanic checked the fuel pump spacer was still present, and also checked the pump was functioning when going up through the rev range. Fuel gets consistent squirted into a jam jar on the output side of the pump. Seems fine.
 
As the problem only occurs under the highest fuel loading (hill climbing at speed), I'm still thinking fuel starvation somehow. Several hours on the motorway at 60mph, no problem. Yet I could force the problem by getting revs over 3500 for any amount of time - guaranteed power loss and having to stop after a very short period of time. Could there be a bit of a vacuum forming in the fuel line?
 
I rarely fill the tank and had been avoiding it just in case, but after a long drive absentmindedly filled the tank completely. Car conked out after just 10 minutes of doing 30-40mph. Maybe a full tank suffers worse?
 
I started checking for a vacuum in the tank by listening for a hiss when opening the vented fuel cap. Possibly heard something so replaced the cap in case it was blocked - no improvement. My tank doesn't have an open vent hose through the boot floor, instead it is attached to a charcoal canister in the wing. The canister is no longer attached properly with vacuum hoses or to the breathers or carb, maybe it's blocked?
 
I have the tank breather hose, non-return valve, breather pipe to canister, and fuel line checked for proper flow - no problems found, so isn't fuel starvation due to vacuum.
 
Back to my mechanic for the final diagnostic and solution - see my next reply!

 



#2 SminkyBazzA

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Posted 04 July 2019 - 10:23 PM   Best Answer

Because the problem started after the fuel pump was removed to replace the seals, we figured that's got to the be problem, however unlikely. We do the jam jar test again, but this time with some prolonged and aggressive revving - suddenly the pump stops pumping at all and doesn't start working again until the engine is stopped.
 
A lightbulb moment occurs, and the pump removed to check something: Result!
 
Apparently the pump is a PITA to reattach in-situ. For those that don't know (as I didn't) it is attached to the engine with two bolts, and has an arm that goes inside the engine block and rides against a cam which actuates the pump. In this case after replacing the seal and getting one bolt attached, the pump was rotated into position slightly to get the second bolt aligned and screwed in. 
 
Without realising it, when it was rotated the fuel pump arm was not properly positioned against the cam face, but was instead pushed against the edge or side of the cam, bending it slightly to one side.
 
Somehow, at lower revs and with gentle driving, there was enough friction/pressure for the side of the cam to operate the pump slightly, but not at the full travel of the arm - I was getting some but not all of the fuel the engine might need. After the engine reached a certain speed or was aggressively driven, the arm would slip completely and not regain traction until the camshaft slowed down sufficiently. Me keeping the revs up as I was changing down the gears didn't let this happen so stalling out was guaranteed. The more often the cam slipped, the more likely it was to again (hence the problem starting to occur at lower speeds).
 
Here's some pictures we took before straightening the arm and carefully reattaching. To test this (officer) I've been driving at all speeds/styles since then without issue.
 
I hope this helps someone else in future, no-one I've spoken to had ever heard of this happening.

 

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#3 ukcooper

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Posted 05 July 2019 - 06:59 AM

 tell you another one to add ro the list, had a 95 sprite hif38 .

 

problem - seemed to run out flue after a mile , then stop run for mile again . and again..

 

after a lot of mucking about , some smsrt ass said try the flue return pipe and so i did just unplued it ean a pipe down under the car , never happed again.

 

I think because there not injection the pipe jets clogged up as no pressure going into it ,it gets a air lock and shuts down ..

 

my 10p worth 







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