FI woes, fuel pump questions

[Ian_G]

OK y'all here is my question:

Are there any aftermarket fuel pumps that reach 30psi?

I've been going all over my 2L with the stumbeling and cold start problems. Guess what, MPS, TPS, FI points, everything is good. However when I monitor the fuel pressure I get constantly changing pressures from 28psi to 36psi. The gauge is bouncing continuiusly and the pump is always running.

Well I happen to have clear fuel lines down at the pump and there is a continuous stream of bubbles in the line. I believe that this is the cause of the erratic fuel pressure readings as well as hard cold starting. The fith injector being high in the system it would tend to pump that line full of air.

SO, the fuel pump is the suspect now. Does anyone have expereice with dieing fuel pumps. Is leaking air one sign?

Ian

[JP Noonan]

Look at the 914 fans web site, and in the PP tech articles I think there is a explination of the fuel pump.

I would say that: If the pump runs then shuts off after 2-4 seconds with engine off key on, then the circut is O.K. If you are saying it stays running then the relay or brain is fouled.

In my experience with 914 and domestic FI cars the fuel pumps get increasingly louder before they die, but then just that, they die. My 72 pump gave my some rough running a day or two before it died but thats about it.

Try pinching off the return line with pliers, the pressure should go up to 40-45 (?not positive, I could try it on mine later) PSI. If it does then it is the fuel pressure regulator that is bad. If the pump still only chugs out a low PSI it is the pump.


One last PC thing:

I am assuming that your FI system (i.e. hoses) are in tip-top shape. Pinching off the fuel line will of coarse increase the pressure. This will in turn tax the system past it's nomal opperating pressure, but should not go past it's safe burst pressure. FI hoses are rated to go this high, but if yours are old then "Pop-Phisssssss". In any case better safe then sorry, bypass the fuel pump relay so the pump runs contiuously with the motor off (and cold!!!) then try the above test. Do not run the pump too long with the motor off (it can over heat) and only pinch the line long enough to get a stable pressure reading.

[This message has been edited by JP Noonan (edited 02-07-2000).]

[Ian_G]

I've replacem most of the fuel lines, there are many. My problem is that there is air in the line. I am assuming that this is comming from the fuel pump as the fuel is solid before the pump and air filled after.

Thus the pump keeps the pressure up, but air in a FI system is not tolerable.

So I was just casting around for two peices of info:

1. Has anyone seen their fuel pump start pumping out air in the line? Or any other air in fuel line story.

2. Has anyone found a cheap fuel pump that can deliver 30spi. The rebuilds are actually cheaper than a generic tha NAPA had.

Thanks
Ian

[John Rogers]

Have you checked the pressure regulator? I checked ours by clamping off the return line with the gauge connected and I also drove the car to see what happened under load. The bubbles could also be caused by a nearly plugged fuel pump suction such as the filter, pickup connecton in the tank. I would recommend a capacity check to to verify no pluggage. Good luck.

[This message has been edited by john rogers (edited 02-07-2000).]

[rich]

I know you stated that you replaced most of the hosed, but recheck for proper size. An incorrect size could allow a small bit of air to be siponed in at the connection. This would also explain the bubbles.

[Ian_G]

I've yet to replace the hose down on the pump. All replaced hose was around the fuel rails and under the gas tank. I'm going to be checking all the connections asap.

Ian

[stelan]

the internal parts of the pump are ok but the casing or seal probably bad,sucking air thru a hole small enough that it wont leak, but big enough for the pump to suck ait thru, so I would say replace the pump, and in my experience, do not try generic or adapted fuel pumps, get the original kind.

Steve

[Ian_G]

OK, I'm comming to the conclusion that getting a decent fuel pump that will put out 30psi will indeed cost more than a replacement pump.

However looking at the two types of pumps there is the pre-'75 and '75-'76. I've a '73 and I'm going to relocate it to the front with this fix. I don't see the value in getting the three port pump when I'm going to be going to the front. Am I right in thinking that the '75-'76 two port pump will work fine in this situation??

Thanks
Ian

BTW the part numbers for the Bosche '75-'76 fuel pump are comming out the same as the primary pump of e30 BMW's. These are '84-92 325's and 318's. Hmmmmm I can probably pull one at the junker for ~$20

[Dave at Pelican Parts]

Well, it can be made to work. Probably the best bet is to find a 75-76 junker and get the plate that mounts the pump and filter, and make some GOOD drawings about where it goes. Then cut the firewall (gas tank out, you don't want to risk cutting it!) for the mounting plate.

Then run a new fuel pump power wire from the original connector (or from the relay board if you're a bit more ambitious) up to the pump. The cleanest installation is to go through the main wiring harness. I've run several more wires, using a coat hanger and some tape. Hint: Pull the rubber "boot" off of the firewall and feed the wires into the boot from the bottom side.

Then you have to get the fuel lines figured. The inlet one is a different diameter, I believe. I don't know what it is. WIth luck the fuel filter has the correct fittings on it so all you have to do is run a line from the tank to the filter, and a short one from the filter to the pump. Then hook a hose from the pump outlet to the center tunnel line. Not sure what OD center tunnel lines the 75-76 cars used; the earlier ones had 9mm supply line and 7mm return line.

You'll still need to hook the return line up to the return port on the bottom of the fuel tank.

Good luck!

--DD

[Ian_G]

HA HA, I found it!!!!

The centre lines are leaking. Mainly the line from the tank to the pump, not the return. This is where I'm getting air in from, and there is a vague gas smell in the cockpit when the car sits closed for weeks.

So I've replaced all the lines except the ones that run through the car. I have to replace these so I'm wondering if y'all have any suggestions on what to expect. Having never dealt with the famous clutch tube or pulling anything through this part of the car I'd like advice on what to expect.

Right now these lines are flexible high-pressure clear hose. My idea is to get aircraft fuel line (9mm) and attach it to the side terminating under the engine. Then just pull her through. Is there any unexpected hinderance to this plan that y'all can see?

Thanks
Ian

[Dave at Pelican Parts]

I would not feel confident with rubber hoses running through the center tunnel. I would NOT drive a car that had SS-braded hoses through the center tunnel. The rubber would seem to be too easy to damage, and the SS braiding likes to cut everything it touches. The brake lines run through the tunnel, as does the main wiring harness....

You can get stainless-steel tubing and use it. Wayne did, and wrote up a tech article.
http://www.pelicanparts.com/techarticles/914_gas_lines/914_replace_gas_lines.htm

--DD

[JP Noonan]

We'll the man has spoken, heed his words for he is wise.

Seriously, I have had the center tunnel line rupture on my 75 with the pump up front. NOT FUN. Between the time I smelled the gas, and stopped the car, there was a 1/2"+ puddle of gas under both seats. Ask any fire rescue guy what a gas fire does to human flesh. Ain't pretty. It's not the fluid that ignites, it's the fumes.

Anyway, I did mine in about 4-6 hours of working, drinking (Pepsi, right?) , working, hanging out, working. The 75 has a PITA exhaust/heating system and a PO had a deep add on oil sump, but I did it with the motor in the car. Things to consider: If you are never going to have a 200 hp 6 then use 7mm (5/16") for supply and return. This simplifies the hoses because the pump outlet is 7mm and the fuel rail is 7mm. Otherwise you need to rig up some kind of 7mm-9mm adapter. Asecond person with small hands helps, they guide the lines through the front grommets from the access hole while you push from the rear. Removing the pedal cluster helps a little if you start to get frustrated (my car has the under dash A/C which is the second biggest PITA). Also use dishwashing soap or electrical wire lubricant to ease the tubes through the grommets. If you have the metal line extend through the engine tin be sure to use a proper grommet (a bulkhead fitting is better) or the tin ware will eventually cut a slice in the line. The factory 75-76 fuel filter has a 7mm inlet and a 12-13mm (?) outlet. Unfortunately the 70-74 tank has a 9mm outlet, so some adaptor is needed or use extra FI clamps (NOTE: FI clamps are much better than normal hose clamps. Hose clamps cut into the hose) on the filter side. While the tank is out have it flushed and clean the pick-up screen.