MFI gurus weigh in - 2.4 S pump on my 2.0 E

[RichMason]

So after a few nights of fiddling around trying to make the cold start work (wired it to the rear window defroster and it works perfectly), I figured out why I have extra wires in the MFI wiring circuit - someone changed out the injection pump to the 013 - 2.4S. The car runs beautifully with great power and it drives as many have described the S engines with little power below 3000-3500 rpm and a turbo-like kick in the rear as you cross 4000 all the way up to the redline. So what happened? Is it common for MFI cars to need a new pump and use the later MFI units in a detuned state or the stock engine or is it more likely that the engine has been modified and more fuel was needed? Although this tells me next to nothing, the E shroud was used and the case is the correct one for a 2.0 from 69. I guess the only way to answer this definatively is a tear-down. Final question, can I run 87 octane fuel as recommended for 2.4 MFI engines in the Porsche MFI tuning manual?

[Rot 911]

The more reasonable explanation is that the previous owner needed to replace his MFI and put on whatever he could find. If it was intentional, as in needing the "S" pump for a modified engine he would also have been smart enough to know how to properly install it! Any modification needing the "S" pump would also entail the "S" cams and intakes. As for octane I would go with what is needed for the 2.0 which I believe was at least 90 octane.

[RichMason]

I agree that the scavenger, first pump available approach makes sense but I get the impression that you just can't install one on a smaller displacement engine, with or without with the wrong cams and have it work well. I am still learning about the basics of 911 engines but changing the cams seems like a big job and changing the displacement, especially by changing the stroke, is a bigger one. What I was wondering is can you put the "brains" of the E pump into an S pump body and have it work? If not, then the engine must have been modified to work (how about a 2.4 crank and p&cs although that would involve some case work). One would probably spend more money making the engine work with an S pump than the cost savings of using whatever pump was laying around if the original E pump was bad.

[724doorE]

I run 87 octane in my 72E with no trouble. It has 8.5:1 RS 2.7 P/c's though. I belive the striped ape syndrone is quite familiar to us early car owners!

[69911e]

If you have plastic stacks it probably has a 2.4s conversion. If it have metal stacks it is probably just a pump replacement, in which case the car would run better on a 2.0E spec pump.
I have run a 2.0E pump on a 2.2E for years with good results(soon to be replaced).

[Paul Thomas]

As long as you're not puffing a bunch of black smoke, backfiring or popping through the stacks i wouldn't worry too much. The MFI pump is a little more versitile than people think. As has been said many times before the main difference btween pumps is the space cam which determines the ammount of fuel injected at various RPM's.
If you have a lack of power below 4000rpm you should deffinately check your pump timing. Mine timing was off one time after i had the pump off of the motor and it behaved exactely like you decribed. The timing procedured has been miswritten quite a bit; you should time the pump at the FE mark 40 degrees after TDC for piston #4 not #1. I had mine on number 1 and had your problem. The MFI system did not get it's rep for throttle response by having a lack of low end power. It has also been said by some that the Factory race mechanics never worried about pump timing much anyway. If this was the case i think it was because, like you said, your car has lots of power above 4000 rpm. Most race cars idle at about that. So why worry about timing if only affects performance in a range that you don't operate in?

Paul

[BK911]

I'm thinking the space cam's most important duty is to time when the fuel gets delivered. So an E space cam should work with E cams regardless of displacement. You would just have to adjust the mixture relatively richer or leaner depending on displacement.

But using one space cam with a different cam would involve MFI timing issues. The fuel wants to get injected right before the intake valve opens. Different cams have different IVO. So theoretically you could figure out the difference in IVO and adjust the MFI timing accordingly. I don't have the T, E and S cam specs available, maybe not an issue?

Maybe, maybe not??

BK

[jluetjen]

I'd also take a ride in another E; preferably a 2.0 E. What you described is pretty much the way mine feels. E's have nothing below 2000 RPM, and come to life at 4000 RPM. I've been told that S's (especially earlier smaller engined cars) are unhappy below 2500 RPM and the torque charts show them coming to life at 4500 RPM.

I would think that an E with an S pump in it would have issues between 4000 and 4500 RPM when the E cam starts pulling but the S pump doesn't pump the fuel to match. Above 4500 and below 4000 RPM I suspect that the engines would require comparable amounts of fuel. I'll have to check the flow charts in the shop manual.

BTW - did you check the screws on the pump to see if they had been opened? If the seals were broken there is the possibility that someone may have rebuilt a 2.4 S pump to 2.0 E specs (go figure). The pump is now a real find since I guess it is the only version which can fit the cam required for a 2.7 RS engine.

As far as fuel goes, I've found that my E runs best on Sunoco's 93 octane - but then I have S pistons which have a 9.9:1 CR and a comparatively poor combustion chamber design when combined with the 2.0 heads.

[RichMason]

John,

Thanks for the informative response. The screws on the pump are painted yellow and are in the same position they were in when they were painted. I need to try and track down another E in the area for comparison. I guess the truth about the engine will need to wait until I need head work. On another topic, I have several different oil leaks that are smoking me out of the car in stop and go traffic. I took off the air cleaners and cleaned up the top of the engine as much as possible with the intakes in place. The hose from the injection pump to under the oil sender (temp? Pressure?) appears to be new and not seeping. However, there was clean oil around the base of the sender. I tightened the connections and I'll see how it does. The larger leak is either the flywheel seal, the cam seal or both. There is oil on the driver's side of the engine compartment behind the injection pump and the belt looks wet. Can the camshaft seal be replaced with the engine in the car? I would like to eliminate all of the leaks I can without dropping the engine to make sure that my problem is the flywheel seal. Any advice would be greatly appreciated.

[tryan]

i had the dreaded pump drive oil leak at the cam. the motor came out twice. two seals worked better that one.

make sure your cold start fuel enrichment line is tucked up out of the way if you are playing around back there. mine rubbed on the injection pump belt. i'm glad i caught it before the impending fire.

[jluetjen]

Now to correct myself (before someone else does!) Here are some charts that should help to clarify the FI pump difference. Porsche was nice enough to include the specific fuel consumption for their engines in the shop and users manual. Take note of the bottom line (Specific Fuel Consumption in g/HPh). Interestingly, the difference in shape is not THAT great between the E and the S. (Note that the scales are slightly different!). It might be interesting to look at this in terms of % of the highest number since part throttle adjustment will move the entire map up/or down, so it really is a case of a difference in shape and total change. I believe that this number is what the space cam essentially controls (in addition to some tweaks up or down based on temperature, etc.)

Here is a comparison in round numbers

Speed.....2.0E.....2.2E.....2.2S....2.4E.....2.4S
2000........243......231.....240......230......238
2500........240......225.....237......225......235
3000........240......222.....235......222......230
3500........240......220.....235......220......225
4000........240......220.....235......220......225
4500........240......220.....237......220......223
5000........245......225.....239......220......225
5500........250......230.....242......225......230
6000........255......242.....250......230......238
6500........270......265.....255......238......250
7000.........NA........NA......265......250......2 70

[jluetjen]

Oops, this one didn't make it on the first upload...



The 2.4 data came from page 3 of Up-Fixin Vol XII.

[jeff m]

Cold start wired to rear window derost!
The cold start relay (which ops cold start sol) is operated from the thermo time switch which gets its 12v from the starter solonoid.
The same 12v is used on the relay too.
This ensures that it will only work whilst starter is turning.
Jeff
911T

[Bob Spindel]

The only real difference between pumps is the space cam,which is a kind of analog computer in that its profile governs the amount of fuel delivered according to **both** rpm and throttle position. It's kind of neat technology, if you think about it. It's also simple. The differences between the various space cams are not all that great, and installing a different cam, or whole pump with a different cam, won't make a very big difference, especially in a 30 year old car that almost certainly suffers from a whole host of parts in the tuning chain that have various degrees of wear (and misadjustment!). The adjustment of the part-load mixture control is **way** more critical.

>So after a few nights of fiddling around trying to make the cold >start work (wired it to the rear window defroster and it works >perfectly)

Clever idea. I take it that your thermo-time switch isn't working or you would wire the cold-start relay to it (That's where it's supposed to go.), and that you simply turn on the rear defroster to start a cold engine, but leave it off when the engine is warm. Nice solution!

I am alomst certain the regular gas was specified for your car and will work. It certainly works in the T's and E's.

Bob

[RichMason]

the rear defroster works switch well but I have to be careful to only use it for a few seconds because it would run continuously since it has power whenever the car is on.

[jluetjen]

Rich;
You might want to look at wiring your cold start switch the way I described in this thread. It will allow you to use your defroster and not stress yourself about forgetting to turn it off. Note that my cold-start circuit only powers up the solinoid when the starter circuit is powered up. If I forget to turn it off it has no affect unless I try to start the car hot. In that case the engine will be too rich to start.

BTW - This trick will only work on the MFI systems from '69 E's and S's. The 70 and later cars no longer had cold start solenoids on the MFI rack.

[RichMason]

John

I looked at your post when I was working on the wiring and that's how I figured out I had the wrong pump - since my pump dates from 72/73, it doesn't have the same solenoids. If I run power to the one solenoid on my current pump, the car won't start. I think what I should do is remove the constant hot from the defroster swith and replace it with a switched hot from the starting circuit. Then I can just turn on the defroster switch and it will only work when the starter is running. That will also remove any voltage bleeding that I may have. The danger with the wiring I have is that if you turn on the defroster while the car is running (or not), it shoots fuel into the stacks, which must be a fire hazard!