Any good MFI people out there?

[LeafGreen]

I have a 72T with a recent stock rebuild of the original 2.4 liter engine (OK - OK, I increased the CR from 7.5:1 to 8.0:1), but that's it. The problem I am having is hard starting .5 - 4 hrs. after the car has been running from a fully warmed up state. It starts up fine cold and immediately after shut down. It seems to be an excessively rich mixture that is preventing a quick start up (foot to the floor to start), but when it's running, it runs like a raped ape! Plugs are tan and fuel mileage is about 15 combined and 22 hwy.

If I understand this FI system correctly, the mech. pump delivers fuel to the injectors at about 200+ PSI, and it's this insane pressure that works against a spring inside the injector to open it. I suspect that the spring pressure holding the small poppet valve closed is a vital part in the proper operation of the whole system. My observation is this: When the engine is shut off, there is a high residual pressure in the lines, and if some or all of the injectors are unable to hold pressure (damaged seat; weak spring), fuel seeps out of the injector into the intake port filling the valve pockets and or cylinders causing this rich condition shortly after shutdown. Does this make sense? I thought about the cold start valve being the culprit, but I unplugged it on several occasions, only to observe no improvement in start up quality.

I have learned quite a bit about this fascinating system in the recent months, but so far have been unable to convince myself it's NOT the injectors causing my problem.

Any ideas would be appreciated.

[gruen911]

Alex,
What the hell is an Olds Tahiti super tiger?

[pwd72s]

http://d240157.u39.zeonhost.com/foru...ead.php?t=4147

[911pcars]

Have you been to this page?

http://www.early911sregistry.org/Resource-MFI.html

Sherwood

[GreenT]

I met Alex at the GAF and we drove back to Norcal together - I can vouch that it runs like the aforementioned ape. I'm sure many of you will remember seeing the car pictured below at the show. Alex is a do-it-yourself kind of guy - not only the paint and body on this car, but he took apart the MFI system, figured it out, fixed it, and put it back together again and then drove it 900 miles to the show and back. Definitely this board's kind of guy! I suggested to him there that he join the registry for the expertise I've found here, and this is his first post - surely the best answer here can't be to send him hat in hand to Gus at Pacific Injection - c'mon experts!

PS - The Super Tiger is a boat - - -

[LeafGreen]

I walked into Lukes and Shoreman a couple of years ago looking for parts, and while I was there I asked some questions about the MFI. The crotchety guy in a cloud of cigarette smoke behind a desk said: "Don't F__ with it!" I replied "But what about the..." he said again "Don't F__ with it!...And when it stops working, put Webbers on it" I knew then I had three options: Fix it myself; Pay cubic$$ to have someone else fix it; Put Webbers on it. I do have a set of Webbers as a back up plan, but I think the MFI is too close to being right to just throw in the towel.

John, I appreciate your confidence - I just hope I can dial it in. By the way, after leaving your house Sun. night my electric fuel pump quit half way home and I was stuck on CC Rd. - that is until I fixed it and drove home. I'll fill you in later.....

Here are a couple of Tahiti Super Tiger's - the yellow one is mine.

[HarryD]

Alex,

I know exactly zero about MFI but what I always see is a plea to follow the procedure in Check, Measure, Adjust . I am assuming you have this document. If not, the link should bring you to a zipped PDF File.

good luck.

[LeafGreen]

Harry,

Yes I have it, It's in the car - along with the appropriate adjustment tools. I'll just keep plugging along. Thanks for the input.

[Spud]

For what its worth my 2.2S MFI car acts in the very same way. Hot start problem only after heat soaking for 10min up to about 40min, wait long enough and it'll fire right up again.

I also have come to the conclusion that it is my injectors (some or all) that are leaking fuel into the cylinders, could be a spec of something keeping one slightly open, or they could just be worn. The best advice I've heard on solving this is to pull them and send them to Gus for a cleaning and a test. He will be able to tell you which ones need replacing.

[rst73]

Alex,
If you really think it's the injectors, have them tested. Any good local Porsche or Mercedes diesel shop should have a Bosch injector tester. I can give you some local shops here in So Cal or send them to me as I purchased one several years ago and would be happy to check them for you. My guess is it is too rich or dirty thermostat washers on the pump, check your CO. I am going by memory only and can check my notes but as I remember factory spec is 3.5-5.0% but 7.0 to 9.5 work very well. Hope this helps.

All the best!

Roger Grago
R Gruppe #27