MFI 911 Running Poorly When Warmed Up

[RSTarga]

I use Stabil Marine gas additive to keep the MFI happy, some use marvel mystery oil

[Jeff Higgins]

I used to add Marvel Mystery Oil to every tank. I was concerned that the MFI pump hails from an era of leaded gasoline, and was concerned that the lack of lead in today's fuels could lead to problems. I thought they might depend on the lead content for some level of protection, like valve seats used to.

Well, I was wrong. This got to be a big enough PIA that I quit doing it over ten years ago. I've had no problems as a result.

I also run ethanol fuels with no issues. Like the mystery oil, it just became to big of a PIA to seek out ethanol free gas, as much as I drive the car.

And here I sit, some fifteen years after building my hot rod 3.0 MFI motor. It now has 108,000 miles on it with nary a problem. I firmly believe that many of the sorts of problems I read about on this forum, like the ones outlined in this thread, are due solely to a lack of use. These things need regular exercise. Left to sit, things dry out, crack, harden and gum up, evaporate and gell, and all sorts of bad things like that. The easiest, most enjoyable "preventative maintenance" is to just get out and drive these things.

[Schulisco]

Jeff,

be careful - a MFI injected 911 might not be that sensible to ethanol than a CIS car. We're talking here about CIS 911. Some CIS components contains rubber diaphragms (fuel accumulator) and seals, like WUR and fuel distributor. They can fail with ethanol over a longer period sitting the car.

The lead in the fuel in earlier times was to protect the inlet and outlet head valves as long as they weren't hardened. From all I know Porsche used on the 911 CIS cars from the beginning hardened valve seats due to stronger emission standards beginning in the 70s in US. The RoW cars benefitted from this as well because Porsche sets the standard on them for the whole production. They foreseen that stronger emission standards will also come in the rest of the world with lead free fuel.

Thomas

[Jeff Higgins]

Thomas - the very title of this thread contains "MFI" - we are discussing brittbolen's woes with MFI, not CIS.

I fully understand the use of lead in gasoline as both a valve seat lubricant and as an anti-knock compound. I grew up through the era during which it was removed from gasoline. I well remember replacing valves and valve seats in a number of motors (Harleys, big block MOPARS) that failed as a result of that change. So, yes, you are correct in that regard, and regarding CIS motors fitted with hardened seats - they were all built in the beginnings of the lead-free gasoline era.

My concern - proven to be unfounded - was that the Bosch engineers were counting on some lead content to help lubricate the plungers and sleeves in an MFI pump. All that part of the pump ever sees is gasoline, no lubricating oil gets into there. Apparently, however, even in the absence of lead, modern gasoline provides sufficient lubrication.

[Schulisco]

Jeff,

you're absolutely right - something here in the thread lead me to CIS instead of MFi. Sorry 'bout that!

I also understand your concern now about the usage of lead into the mechanical fuel pump.

From all I know - lead was used especially on components operating at very high temperatures like valve seats and others. But here the lead was also used for "lubrication" as well. Also it reduced the knocking on the engine while lead increases the octane rating as well.

Due to the MFI pump is not operating at very high temperatures, the usage of lead / lead subsititute is not necessary / useless as you experienced on yours.

Thomas

[RSTarga]

Originally Posted by Jeff Higgins

I used to add Marvel Mystery Oil to every tank. I was concerned that the MFI pump hails from an era of leaded gasoline, and was concerned that the lack of lead in today's fuels could lead to problems. I thought they might depend on the lead content for some level of protection, like valve seats used to.

Well, I was wrong. This got to be a big enough PIA that I quit doing it over ten years ago. I've had no problems as a result.

I also run ethanol fuels with no issues. Like the mystery oil, it just became to big of a PIA to seek out ethanol free gas, as much as I drive the car.

And here I sit, some fifteen years after building my hot rod 3.0 MFI motor. It now has 108,000 miles on it with nary a problem. I firmly believe that many of the sorts of problems I read about on this forum, like the ones outlined in this thread, are due solely to a lack of use. These things need regular exercise. Left to sit, things dry out, crack, harden and gum up, evaporate and gell, and all sorts of bad things like that. The easiest, most enjoyable "preventative maintenance" is to just get out and drive these things.

You are correct, when I drove my car all the time, I used no additives. I don't get to drive it as often anymore and use the stabil to keep the fueling better shape.
I think any fuel hoses do have to be upgraded to ethanol resistance specs. With my 8.5 compression I don't even use Premium, at least in the cooler months.

[Jeff Higgins]

Originally Posted by Schulisco

Jeff,

you're absolutely right - something here in the thread lead me to CIS instead of MFi. Sorry 'bout that!

I also understand your concern now about the usage of lead into the mechanical fuel pump.

From all I know - lead was used especially on components operating at very high temperatures like valve seats and others. But here the lead was also used for "lubrication" as well. Also it reduced the knocking on the engine while lead increases the octane rating as well.

Due to the MFI pump is not operating at very high temperatures, the usage of lead / lead subsititute is not necessary / useless as you experienced on yours.

Thomas

Yup, I was needlessly worried. I think what it boiled down to was that the lead worked well on the valve seats as you describe, with their rather unique high temperature / high seat pressure condition. I think I remember that the lead provided somewhat of a "cushion" that other additives do not. So, I think the other additives might possibly provide the lubricity, just not the "cushioning", so they work well elsewhere, like in our MFI pumps.

Originally Posted by RSTarga

You are correct, when I drove my car all the time, I used no additives. I don't get to drive it as often anymore and use the stabil to keep the fueling better shape.
I think any fuel hoses do have to be upgraded to ethanol resistance specs. With my 8.5 compression I don't even use Premium, at least in the cooler months.

I've read about the concern over rubber fuel system components in many different sources. All I know is that in my '72 and my son's '68, both MFI cars, we have never ran into these issues. Nor in my other son's '78 SC. Granted, as old as these cars are now, we have been through all of them replacing pretty much every piece of rubber they were delivered with, but that's expected. Fuel lines, brake lines, weather stripping, window seals, etc. So maybe we are still "in the window" as far as ethanol related degradation.

The only machine, car or motorcycle where I have experienced verified ethanol damage was in my 2003 Boxster S. The submerged fuel pump and fuel filter failed, having had their plastic and rubber components damaged by ethanol. Other than that, I've been lucky and have not experienced this in other vehicles.