I just transplanted my main fuel pump from my 89 1.8l digifant golf into my
86 CIS-E as it was intermittantly dying and refusing to start. Initially this seems to have worked. The part number was slightly different from one pump to the other. Is there anything wrong with doing this? I had someone else tell me that it shouldn't even work but I can assure you it's working as of right now.Thanks for any info,
-Andrew
I thought the CIS-E cars ran at much higher pressure than Digifant, but check the Bentley.
Could be but could the fuel distributor (CIS-E) and fuel pressure regulator (Digifant) ultimately be regulating that and not the fuel pump itself?
The big difference is the fuel delivery rate,. Digifant pumps are designed to deliver a min. 500 cc. (17 oz) /30 secs, the CIS, CIS-E are dependant on the actual voltage and can range from 300 cc at 9 volts to
760 cc at 12 volts. Under easy running conditions then the system should be able to maintain pressure with 500 cc constant delivery, but if you have a heavy foot or try to speed away, you may not get enough fuel to maintain the required pressure because you're burning the gas faster then the pump can deliver it.The low pressure digifant system doesn't need the flow that the CIS and CIS-E need. so indirectly the fuel pressure comment wasn't that far off.
A pressure regulator bleeds off excess pressure by returning it to the tank. If the pump is incapable of generating the pressure you need to operate the system (regardless of its capability of delivering fuel volume or weight) then the pressure regulator isn't going to be of much help.
But this is all based on the premise that the CIS-E pump delivers higher pressure, and I don't know that it does.
Think what you like, but you're wrong... First off, fuel flow varies with voltage (and pressure) on all pumps, almost by definition. The motor speed that turns the pump varies proportionally with voltage (at least to the first order). It's not like in CIS/CIS-E cars you have any control over pump voltage. It is whatever it is.
The fact is, in any car the amount of fuel consumed is going to directly depend on the amount of air thats coming into the engine and how much power its making. And the minimum amount of fuel you need to deliver is exactly as much as you consume. At least among
8V cars, the Digifant cars were making about the same power as the CIS-E cars, and since there's a large margin of safety on fuel delivery, both Digifant and CIS-E pumps are capable of delivering the amount of fuel needed to operate either fuel injection system.The problem is Digifant cars need that fuel to be delivered at about
40-45 psi. CIS-E cars need the fuel delivered at 75 psi. A Digifant pump will have a very hard time delivering fuel at 75 psi. You might get a little fuel, but it'll be very little, no where near the 500 cc/30 seconds that the book claims. You could probably put a a CIS pump in a Digifant car because as Matt pointed out the regulator will drop the pressure down to what Digifant needs.Incidentily, a good rule of thumb is you are good for 2.5-3 hp per liter per hour. So even 300cc/30 secs = 36 lph ~ 100 hp. So you might starve it a little if your at WOT@6000 rpm, but if you just went by fuel flow, even at 300cc/30 secs, you're more than adequate for most conditions, not just when you are taking it easy.
If you don't believe me, see a few websites:
Other than concern for possible fuel line leaks or joint leaks, don't see any contigent for concern. My CIS fuel pump in 88 VW Fox wagon is rated a 80 psi per VW. I've replaced due to fouled tank due to rust, that's when I got that info. I would watch the spark plugs for lean mixture, meaning the pump isn't keeping up with the engine requirements. All else being equal of course.
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