fuel pressure problem?

mabbo · Post by **mabbo** » Sun Aug 19, 2007 7:51 am

Hello guys...

iv been having problems with my 1988 VW Beetle being hard 2 start, and randomly cutting out, and now unstable AFR readings... its a 1955cc type 1 engine with MS1 V3 Megasquirt and a TD04 turbo.

here is some background info...

car is now on the 3rd fuel pump (first 2 second hand, the 1 im using now is a new bosch part, rated at 3psi) and i had a cheap ebay adjustable pressure reg with a gauge, but am now using a stock bosch regulator from a vauxhall... think its set at 2.5psi factory - part number 0280 160 221.

anyway, i have a feeling iv had fuel pressure related problems since i got megasquirt working, but im not 100% sure... this is whats been happening.

i got my car running pretty good, then it started running crap and then after a while, it kept cutting out whilst driving under load and the AFR reading 20:1, then the AFR would go back to around 14:1 and the engine would kick back in.

i thought the problem was fuel related and noticed the fuel pressure gauge was moving up and down a little when the car was idling... i cant see the gauge when moving, its in the engine bay... but it was set to 3.5psi. the fuel pump was also quite loud whilst operating.

as i thought fuel pressure was the problem, i changed the fuel pump from the 2nd hand bosch item, to a new bosch item from a saab 9000 and also changed my adjustable regulator to my friends bosch item. this seemed to make it better... had one journey and i thought the problem was solved.

the car was driving ok, then it started to not idle v.well but i didnt have my laptop plugged in to see what the problem was. it cut out, and wouldnt start. after much head scratching i noticed there were problems with the fuel pump priming pule... when i turned the ignition on, the fuel pump would not pump smoothly for the 4 or 5 seconds as it should, it kept cutting in and out, i traced the problem to a bad earth from the pump. fixed this and she started up after a few turns and i thought id solved the problem again.

i got home ok, and then it started playign up again, same sort of problems, AFR was randomly all over the place (usually lean when under load) it would be ok for a while, then all of a sudden the AFR gauge would be really lean and the car a pain to drive, especially around tick over as it didnt want to idle, and when i pressed accellerator it sounded like it was going to cut out.

the car finally cut out in traffic and then it was hard 2 start.... when i got her going, i logged my journey back and the AFR was really lean all the time, with quite a few spots worse than others. to keep it idling i had to hold my foot on the gas to keep it above 1500rpm-2000rpm else any lower and the car would try to cut out and the revs wouldnt pick up v.easily.

the fuel pump is now making a vibrating noise again, louder than usual...

does anyone have any ideas what else this could be? im pretty sure its not the fuel pump now, or the regulator...

the only other things i can think is that its maybe:
- the wiring for the fuel pump, but im not sure if these would cause my problems?
- the fuel pump isnt manly enough (its rated 3psi, fuel pressure reg is 2.5 i think),
- a kink in the fuel line from tank to pump, but im pretty sure its not that.#

sorry for the long post.

mabbo

66fb · Post by **66fb** » Sun Aug 19, 2007 8:30 am

mabbo,

The pressure is probably 2.5 bar, the 2.5 psi would be low for a carb setup.

Low voltage to the fuel pump will cause mine to make a louder noise. Fuel pump circuit wire gauge, wiring connections, fuel pump relay contacts and coil connections should be checked -also any fuel filter installed.

As you mention the line from the tank to the pump...could there be an obstruction of the pickup inside the fuel tank? Is the pump installed so that it is lower then the fuel level in the tank? EFI pumps have problems on the suction side.

Hope this helps,

AL

mabbo · Post by **mabbo** » Sun Aug 19, 2007 9:18 am

Hello mate,
Sorry, i meant 2.5 bar... i dont know why i put psi.
I have a plastic inline filter between the tank and pump.
Im pretty sure there are no obstructions from te outlet of the tank, and i checked the hose from the tank outlet to the pump, and i couldnt see any tight bends or other obstructions.
The pump is lower than the tank, it sits right below the tank.
Thanks,
Mabbo

66fb · Post by **66fb** » Sun Aug 19, 2007 9:45 am

mabbo,

Im pretty sure there are no obstructions from te outlet of the tank, and i checked the hose from the tank outlet to the pump, and i couldnt see any tight bends or other obstructions.

Check for an obstruction INSIDE the tank in the area where the fuel line connection/pickup is located. A bit of help to your fuel pump would be to move the filter (may have to get one rated for higher pressure) from the suction side to the pressure side.

I have a friend, we both did MS at the same time, and he had pressure problems. His 3rd pump install looks to be a good one.

AL

mabbo · Post by **mabbo** » Sun Aug 19, 2007 10:00 am

ok, ill check the inside of the tank...

ill get rid of the filter and get a high pressure one as well if that will help.

r1ch1e · Post by **r1ch1e** » Wed Aug 22, 2007 12:24 pm

A lot of the external pumps need filtering before the pump, it sounds like possibly your picking up dirt and sediment from the tank which is giving the pump some grief.

66fb · Post by **66fb** » Wed Aug 22, 2007 1:23 pm

A lot of the external pumps need filtering before the pump, it sounds like possibly your picking up dirt and sediment from the tank which is giving the pump some grief.

From Ford's Engine Installation and Tuning Tips:

"Fuel should be pushed through the fuel filter.
Pulling fuel through a filter can cause cavitation."

AL

jonfx4com · Post by **jonfx4com** » Fri Aug 24, 2007 4:53 am

My tank was not in good shape and after killing a couple of pumps I now filter before the pump and have not noticed any problems. My filter is around 18" from the tank outlet and about the same from the pump inlet. The filters are GM all metal standard injection type units.

Thse type: http://i17.ebayimg.com/01/i/000/af/85/38d7_1.JPG

about 3" diameter

Works for me!

Jon

Tommy · Post by **Tommy** » Sat Aug 25, 2007 1:33 am

66fb wrote: From Ford's Engine Installation and Tuning Tips:

"Fuel should be pushed through the fuel filter.
Pulling fuel through a filter can cause cavitation."

AL

You should have a coarse (100micron) filter before the pump, and a paper element (10micron) high pressure filter after the pump.

Tommy