![]() |
MFI running rich... preheater or wrong pump?
Member
Registered: Apr 2006 Location: Southampton,Ma Posts: 57 MFI preheater and I spoke with the Tom who has the 70 911E on eBay right now. He has had problems with the MFI running right when cold. It sputters and stumbles when first started & then runs great after 20 minutes. Even after a hot start, it runs rich. Turns out the engine was rebuilt at some point and the case has a T serial number. I wonder if someone tried to put an E MFI unit on top of a T engine w/ T heads & cam and all. I remember reading that the T's, E's & S's all had different cams, MFI pumps and settings/timing. Would an E MFI even run well when a T engine is warm? The MFI pump was sent out west to be rebuilt. Cold running improved but still isn't perfect. Do the heads have a casting that will id them as T, or E spec? How about the MFI pump or housing? I thought there was some kind of pre heater that helped tame the cold start beast? he wasn't sure either. j |
Even in stock set-up - at this age, they all run somewhat rich.
Post the serial number of the pump and the engine, and members far more knowledgeable than I can tell you if they go together. But I will tell you, my t engine with "almost s" pistons (CR9.5:1) aand E ported heads and cams STILL runs rich! |
Anything is possible. Without a rebuild sheet you don't know what you have unless you break down the motor.
That being said these older cars do run rich by nowadays standards but that's to be expected. The question is how rich is it running. A exhaust analyzer will give you that answer. You might also try recording your gas mileage and compare that with the factory specs. This will let you know if you are in the ballpark. Also keep in mind that MFI cars are a compromise as all cars are to a certain extent. It's not uncommon for them to be set rich on purpose at idle to compensate for not leaning out to much under load. There are gobs of info on this and a search will show many threads. There should be a pre-heater hose going from the left heat exchanger to the thermostat on the MFI pump. IF not then you need one. |
from what i have read. the injection pump should match the motor cam. the biggest difference would be a s motor with a t injection pump. i'm sure that it is possible to change the inbjection timing to match but it will take a lot of time.
example. 911t motor with 911e mfi. i think the t cam opens at 20deg atdc and the e 20 deg btdc. so the injection pump should be retarded 40 deg. so set the pump mark 40 deg off of the z1 mark on the crank. i don't think that it is impossible to tune good. but to tune it great could be impossible. the thing should just scream from 5-7k rpm the cold start is a normal issue with mfi and there are a bunch of resourses to help with that. i would recomend that you drive the car. it will be quickly aparent that the car is running good or will require a lot of tuning. at least have the guy make a video of him going through the gears and check it out. you don't want to buy a frankenstein porsche blind-folded. do your research and make an informed decision. |
Quote:
The space cam has a different profile which delivers more fuel to match the increased air requirements of the various engines. |
The other "usual suspect" is just the proper cold/warm tuning of the MFI system, much of which is outside the pump. So many of the MFI systems have been kludged by mechanics who didn't know how to fix the problem, but rather only how to get the car started.
|
On MFI, the cold start and warmup thermostat [which is fed hot air, continuously] are different issues and totally different systems! Preheated air intake to the air filter is a THIRD, independent system, not really required!
Lots of misconceptions out there, and confusion with other injection systems! Lots of things need to be determined about a rebuilt engine ... before worrying about which MFI pump is correct! 1. Which engine cams? Overlap TDC intake lift value will tell! 2. Which cylinders and pistons? Cast iron, Biral, or Nikasil? Forged or cast pistons, which valve reliefs? 3. Displacement? A 2.7 can look just like a 2.4! 4. What does the MFI pump ID plate no. indicate? Lots of ways an MFI engine can be maladjusted and messed up by inept wrench or P.O. ... it can be a long process to straighten out! |
Bump
Please post the engine number, type number and the Bosch pump number. This will give a start on figuring out what you have and how to get it running correctly. The next steps will be to measure the cam timing and throttle body diameter. All relatively easy. Finally you need to do a through CMA. We can help. Best, Grady |
All times are GMT -8. The time now is 03:43 PM. |
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2025, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2025 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website