Hello, hello! The new to me 914 is so rad! Love it... went out for a bit of cruise and about 20+ mins into the drive, while approaching a trafific light ( red ) the car came down to idle and that kept going and poof... stall. It did not start, I blocked the lane and angry SUV's and Tesla's honked at me. I did however get it going again after putting the pedal to the floor while starting and it fired up and drove fine, until... idle at the stop sign. Poof, stall. BUT this time pedal to the floor and fired right up.

Thoughts, where should I begin. I have attached a video of the issue... thanks! Beep Beep.


https://www.youtube.com/watch?v=Mx47LENYFuU

I think the first general question would be carbs or FI?

So sorry! What is the year and fuel system? Carb or injected?

Watched your video. By video title it says stock so I'm going to roll with fuel injected.

Problem is I think you're looking for an easy agreed upon solution to your problem. You're going to get plenty of opinions or "his fixed my car" responses which might help or might have zero applicability to your problem and will keep you running in circles.

If you're new to 914's, and 50 year old fuel injection, you should probably start familiarizing yourself with the Brad Anders pages and the overview of D-jet fuel injection components and how to troubleshoot them.

https://members.rennlist.com/pbanders/DJetP...tm#troubleshoot

So it takes about 20 min's before this happens? If so I think we can rule out vacuum leaks as that would increase the idle speed. Rule out the TPS idle circuit as that would be wonky warm or cold. Does your ECU have a black know on top. If so that controls the idle circuit. You can figit with that. IIRC, it has 22 clicks rich to lean. If that does nothing check to see.if the vacuum is holding on the MPS. That's also in Blander's D Jet Bible. Once warmed up check the ohm reading on the CHT sender on cylinder 3. The values are also listed in Blander's Bible. If you have L Jet disregard everything I said. Good luck and if it with you too much throw a Subaru drive train in it.

Good question, it is FI

It is all good! It is a 73 1.7 with FI

factory workshop manual

you can download.

http://p914-6info.net/Manuals.htm

Yup, 73 1.7 with FI.

Of course I am looking for the easy fix but know that is not what is going to happen, I do however need to start somewhere. Thanks for the link! I will be reading that one!

Excellent! A bunch to dig into here! Thx… many subie 914’s out there?

First test is simple, get a hand vacuum pump with a gauge, test the MPS, pull 10 to 15 in Hg and see how long it takes to drop.
Sounds like a cracked diaphragm, runs rich when that happens.

Was my first thought, since I had similar symptoms with the 2L D-Jet.

If you're running stock D-Jet, and you have more than say, 75-100k miles on the car, you have no evidence that the diaphragm has ever been replaced, then I'd wager a dollar to every donut that your diaphragm needs to be replaced. The MPS was a very clever design for its time but that diaphragm has a life limit before it will absolutely fatigue.

Mine had those, and other symptoms, and it actually passed the vac test! But when Tangerine pulled it apart to rebuild the crack was obvious. And replacing it transformed the way the car drove.

I like D-Jet, I think it's worth saving. Consider sending your MPS to Chris for a new diaphragm, even if it passes a vac test.

http://www.tangerineracing.com/mpsdiaphragm.htm

An easy fix is to plan your trips to be less than 20 minutes

I have this one on the list, I will go down the list and start checking them off.

I don't have the pump/gauge but can pick one up.

I will have to remove the MPS?

haha... basically what I have been doing

Cool, I will do this test. Thanks!

https://youtu.be/3lvTXN7d5-8

This seems like a good video/resource

Yes, that will show you how to test the vacuum integrity and the primary/secondary coil wiring. For troubleshooting MPS and other 914 problems in general, another good resource is the Tech Notebook: https://bowlsby.net/914/Classic/TechNotebook.htm, see Reference Manual section.

Can you hear the pump run when it’s acting up and you first turn the key on?

I’ve got a vacuum test gauge , a fuel pressure test gauge and ohm meter if you want to borrow

Brant

Thanks Brant, I will have to replicate the issue and see if the pump is running, from cold start it is running. The issue starts after the car is hot.

Appreciate the offer of the tools. I might take you up on it.

CT

This is a MittyvacII. You will know if the diaphragm is spent in short order. Silly question, have you replaced the fuel filter?

I just did the vacuum test on MPS and I could not get the pressure above 10 and immediately would drop down.

So, if this not the issue, it is ONE of the issues.

All, thanks for the replies and insights

I tested the map sensor with a handheld vacuum test and it failed. Recored the test.


Vacuum Test

So that creates an ultra rich condition and the reason the car would flood out at idle

Should be rich all the time

There is also an O’ring inside to seal the MPS case hallves
I’ve seen the oring crack also. But most likely it is the diaphragm

It can take a couple of hours to disassemble with a heat gun while getting the epoxy from the threads

Don’t force it
As it’s easy to damage the aluminum plug adjustment threads
Requires a discontinued wave tech meter or an AFR to readjust the mixture upon reassembling

Takes a lot of time to get it right
But on the plus side. It can be adjusted for todays fuel and more accurate than a stock one adjusted for the fuel available 50 years ago

The previous owner of the car had an extra MPS unit and reached out after he saw my post on here. I drove down and grabbed it today! it holds pressure and I think the car is good now, no stalling (yet). If anything it is lean now, idle is really low and the acceleration has dropped off just a tinge. Rad community! so cool.

Thanks.