Cold Start Issue 914-4, Admitting I'm stuck and asking for help Options

[Blue Lightning]

Car: 1976 2.0, FI

Background: bought in November last year. I am least the 4th owner. Drove a couple times, then plugged up the fuel filter (? no fuel pressure when the fuel pump was running, but see note below on replacing the fuel pressure regulator), so spent a couple months with the gas tank out and replacing the fuel lines, pump (and yes, filter). Read a lot in the meantime, so corrected vacuum line issues (vac advance was connected, replaced all the lines that didn't already look new, added hose clamps). But where the car started and ran well last year, I can't get it to happily start any longer. While cranking, it will skip and catch. After a few minutes of cranking (and skipping and catching) it will finally start and run fine for a few minutes but only idle around 1000 rpm (until the AAR warms up the rest of the way?), then dies. Starter fluid has no effect, so guessing it is running rich? Pulling the air hose off the cold start injector while running causes the idle to increase to maybe 1400 rpm (but with hunting, as you might expect with that big leak). There are a lot of threads on what to look for when the engine is running lean, but few on it running rich.

Some things I have checked:
- AAR works (https://youtu.be/YmO1ZCLDB7g)
- Compression is good (130-140 psi cold)
- Replaced the MPS last weekend with new one from autoatlanta, after finding the previous one would not hold a vacuum
- Replaced fuel pressure regulator after finding it bad (yes, I've been told these never go bad, but this one would not hold any pressure). Fuel pressure set to ~29 psi.
- Timing is good (~27 degrees at 3500 rpm with vac retard disconnected)
- Vac retard mechanism is working (checked with vacuum pump)
- Spark on all 4 cylinders (checked by timing light)
- Smoke tested the intake...only leaks now are the bearings on the throttle plate
- CHT reads 2k at cold, ~250ohms at warm/hot (at splice connector)
- Plugs look okay (see attached)
- Fuel injectors are all spitting fuel (checked into bottles...all about the same) and have new seals
- idle adjust screw has some control, but I cannot get the idle above 1000 rpm with it
- valves adjusted back in December (my first time, but the car runs so I assume I didn't do too bad of a job?)

I'm at a loss of what to try next. (IMG:style_emoticons/default/hissyfit.gif) I'd like to consider myself fairly good with cars (we have a 1966 Mustang, as well as a Mazda RX-8 that I have kept running for >20 years), but I'm about ready to throw in the towel and have the 914 towed to someone smarter than me!

Thoughts?

[Superhawk996]

No immediate answer but let’s work through this

Where is the insane high pitch whistle coming from? Seems to be the air bypass as it changes when you adjust. But also seemed to be reduced when you tried to put the air filter on.

Were those backfires around 6:17 - 6:20? Those don’t seem to start until the engine warms. At the end of the 8 minutes or so - how hot are the heads? Do you have a means to gauge the head temp at the end when it starts running rough? We could also go by CHT resistance at the end.

The extended cranking to start is not right. If you shot a little starting fluid at the very beginning when it’s extended cranking and dead cold, does that help or hurt?

That it actually runs and revs is more than I got out of reading the initial posts. The video is helpful.

You mention that the MPS is new / rebuilt from AA?:
1) is the part number correct and matching the ECU and the rest of the system? Ie - not all MPS are the same.
2) have you vacuum checked the new one? For some reason I’m assuming yes but not sure.
3) what vacuum level are you pulling on the plenum? I’m wondering if that whistle is a huge vacuum leak somewhere that is killing the plenum vacuum

[Blue Lightning]

No immediate answer but let’s work through this

Where is the insane high pitch whistle coming from? Seems to be the air bypass as it changes when you adjust. But also seemed to be reduced when you tried to put the air filter on.

Were those backfires around 6:17 - 6:20? Those don’t seem to start until the engine warms. At the end of the 8 minutes or so - how hot are the heads? Do you have a means to gauge the head temp at the end when it starts running rough? We could also go by CHT resistance at the end.

The extended cranking to start is not right. If you shot a little starting fluid at the very beginning when it’s extended cranking and dead cold, does that help or hurt?

That it actually runs and revs is more than I got out of reading the initial posts. The video is helpful.

You mention that the MPS is new / rebuilt from AA?:
1) is the part number correct and matching the ECU and the rest of the system? Ie - not all MPS are the same.
2) have you vacuum checked the new one? For some reason I’m assuming yes but not sure.
3) what vacuum level are you pulling on the plenum? I’m wondering if that whistle is a huge vacuum leak somewhere that is killing the plenum vacuum

Yes backfires. That's why I was reaching to shut it off...don't want to wreck anything.

The MPS is the "Euro" version. I had a 043 and when I went by AA George Hussey recommended going with the 037 "Euro" part instead (and he had those, but no 043s). And yes, have vacuum tested the new part several times (IMG:style_emoticons/default/smile.gif)

The screaming seems to be air leaking around the throttle plate or going through the idle air passage. When I put the filter on, I think you are just hearing the sound attenuation from that. In carbureted cars I own, I would set the gap between the throttle plate and the throttle body to control the amount of air/vacuum at idle, but that doesn't seem to be a thing for the 914 throttle bodies (just the idle air screw). I'm beginning to wonder if something is in the idle air passage in the throttle body...

I have CHTs under the spark plugs on cylinders 2 & 4. Both show around 200F after the ~8 minute video. The gauges are somewhat coarse and I didn't look that closely at them this time, so could easily be +/-50F.

I have done smoke testing of the intake to track down leaks. The setup I have (https://www.amazon.com/dp/B06XHRBKTM) uses compressed air with a can that generates smoke that you plumb into the intake plenum, then look to see where it comes out. The compressed air is pretty effective at pushing smoke through any small opening. I eliminated several leaks with this. The largest one remaining that I am aware of is the throttle body bushings for the throttle plate. The car has around 83k miles on it, so this shouldn't be excessively worn, but was going to look at rebuilding it this fall.

When I spray starting fluid in the intake while it is running, and it tries to die, this is what made me think I am running rich.

Going to go check the plenum vacuum

[Superhawk996]

The MPS is the "Euro" version. I had a 043 and when I went by AA George Hussey recommended going with the 037 "Euro" part instead (and he had those, but no 043s). And yes, have vacuum tested the new part several times (IMG:style_emoticons/default/smile.gif)

So AA is back up to the old tricks? (IMG:style_emoticons/default/chair.gif)

Parts should not be mix and match. An 037 is not an 043 which is why it has a different part number.

The 037 is for the 73’. However, the 73 1.7L and the 2.0L use the same ECU and have some “tricks” played with the CHT and the calibration of the MPS to differentiate the calibrations to compensate for the 1.7L to 2.0L displacement change while using the same ECU. Both the MPS and the EcU for 73’ are different than the 76’ setup.

I assume you’re aware of the Brad Anders parts lists and the recommendation not to mix and match.


The MPS you have can be retuned but that isn’t part of what you bargained for. There is some bench calibration that can be done but per the guys (like Emery) that have retuned their MPS, you will really want to tune it on-road with a wide band air fuel meter.

Don’t get me wrong, I don’t think all of your difficulties are related to the MPS.

I’d focus in the short term on figuring out why your vacuum is wonky (didn’t see video) just the gauge pic. The back firing after it warmed up and some of the early “airy” “chuffing” type noise when it was cold, immediately after starting, could be related to a poor valve adjustment that is too tight and leaving valves slightly open. With air cooled engines, better to have valves adjusted on the loose side. Heads run hotter than water pumpers and valve lash tightens as the aluminum pushrods expand as they get hotter.

Temp after 8 minutes seems plausible.

Agree that when you sprayed the starting fluid and it decreases rpm that you’re running rich by that point. Your sooty plugs also say that.

Would really like to see you try the starting fluid when dead cold and during the 1st cranking and see if it catches / fires more enthusiastically. Open throttle - a couple squirts into the plenum, then crank.

After that I’d probably be going back to check your static timing to see if that is contributing to the extended cranking times and failure to fire right away.