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

[Superhawk996]

Reasonable plan.

[Blue Lightning]

Still no bueno. Added a jumper cable between the battery negative terminal and the engine, plugged off the cold-start injector fuel line, and plugged the vacuum lines on the decell valve. None of this seems to have made a change.

Video of run at https://www.youtube.com/watch?v=9xbr0VjFFkE
~1:20 adjusted the idle air bleed screw. At the end, it is backed out so far it is almost falling out of the throttle body, but I get the idle up to 1400 RPM.
~2:10 checked fuel pressure (30 psi)
~2:15 couple shots of starting fluid, which almost kill engine
~4:20 rev up to ~4k RPM
~6:30 starts to die (AAR fully closed at this point?)
~7:45 added the PO's air filter, which make things worse

Note that I cranked the engine for a minute or two before starting the recording, then pulled a spark plug (which looked the same as the previous pictures...no obvious fuel or oil fouling).

[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

[emerygt350]

Very interesting.
Did you ever try a different coil?

That super slow start really makes me think something is wrong with the timing.

I also agree with hawk about that mps. Time to cheat it. Do you have a vacuum pump? You can pop that on the mps and set the vacuum yourself.
Have you tried just retarding the Timing a bit and see how that affects startup? If there is no effect from that I would definitely look at the coil


After that,
If I were you I would
1) do the stuff that hawk mentioned
2) plug all the holes on the plenum
3) attach a vacuum pump to the mps and set it at 22inhg and try to start the car. As you release vacuum the mps will richen the mix.

[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

[emerygt350]

If it isn't pulling enough vacuum it could be your valve job....

[Blue Lightning]

Very interesting.
Did you ever try a different coil?

That super slow start really makes me think something is wrong with the timing.

I also agree with hawk about that mps. Time to cheat it. Do you have a vacuum pump? You can pop that on the mps and set the vacuum yourself.
Have you tried just retarding the Timing a bit and see how that affects startup? If there is no effect from that I would definitely look at the coil


After that,
If I were you I would
1) do the stuff that hawk mentioned
2) plug all the holes on the plenum
3) attach a vacuum pump to the mps and set it at 22inhg and try to start the car. As you release vacuum the mps will richen the mix.

Didn't try a different coil, as I was getting visible spark on all 4 plugs.

I checked the vacuum at idle...and it is pretty bad: https://youtu.be/XOzUYy50ztY
Guess I'm going leak detecting again...maybe I need to check the valve adjustment I did again?

Toward the end of that video, I have the vacuum pump pulling on the MPS, and the idle speed increases significantly (until I hit around 15 inHg, where it dies).

[Blue Lightning]

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.

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

Move video around the throttle body: https://youtu.be/lWhufzgEm3M

as mentioned in my reply to emerygt350,the plenum vacuum is pretty low, so that would seem to be the problem...

[sholman5]

Silly question. Have you checked to see what position of the knob of the ecu is in. Full CCW lean, full CW rich. It does affect the idle.

[Blue Lightning]

Silly question. Have you checked to see what position of the knob of the ecu is in. Full CCW lean, full CW rich. It does affect the idle.

It is currently in the middle. Rotating it does effect my idle, so I don't think it is broken. But I haven't found it to improve the starting.

[emerygt350]

The video is set as private.

[emerygt350]

I can only think valves or something worse. Was the spark awesome?

[emerygt350]

That sound isn't outrageous, that's what it sounds like when your idle screw is all the way out. Mine is the same.

[sholman5]

For quite awhile I had trouble with the idle and up to temperature. During a hot start I had to wfo the throttle body. Would not idle well (surging or hunting) below 1100 rpm. Finally I changed the distributor cap and rotor. Source a good used set of FI trigger points and Bosch blue coil. There was a connector between the cht and wire to the ecu. I thought that it was a shield to keep heat away from the connection. Removed the connector and problem solved. Come to find out it was a 275 ohms resistor, which think only belongs on a 73 2.0. I feel your pain. Hope that you get it all worked out.

[Blue Lightning]

The video is set as private.

Oops, sorry, didn't click all the way through on YouTube when posting it. Should be good now.

[Blue Lightning]

Come to find out it was a 275 ohms resistor, which think only belongs on a 73 2.0. I feel your pain. Hope that you get it all worked out.

I've heard of these. AutoAtlanta sells one which they mark as being for all years: https://www.autoatlanta.com/Porsche-914-Bal...1460610100.html

Supposed to slow down the warmup cycle and help warm-start situations.

I'm sure it will get worked out. Just a matter of whether I can figure it out myself, or need to pay someone else to figure it out (IMG:style_emoticons/default/smile.gif)

[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.

[Superhawk996]

Come to find out it was a 275 ohms resistor, which think only belongs on a 73 2.0. I feel your pain. Hope that you get it all worked out.

I've heard of these. AutoAtlanta sells one which they mark as being for all years:

Supposed to slow down the warmup cycle and help warm-start situations.

Again (IMG:style_emoticons/default/chair.gif) that resistor is not for all years.

That ballast resistor is for 73’ only and is related again to the use of the same ECU between the 1.7L and the 2.0L in 73’ only.

If you look back on the CHT resistance vs temp chart I posted (post #32) you will see that plotted the 017 CHT (73’) sensor vs the 012 temp sensor. The 73’ CHT is the 017 sensor with a different curve and that 017 CHT sensor is rare as hens teeth. This 017 sensor is the one that uses the additional 270 ohm ballast resistor.

If you look at the exponential nature of the CHT curves at low temperature and the rate at which they change during warm up, you will see that adding a fixed ballast resistor will do nothing to slow the down the warmup.

You do not want to be adding the ballast resistor to the 76’ system. You are already running too rich (soot on plugs) - the last thing you want to be doing is running even richer due to the ballast resistor.

(Edit) I’m assuming that since your car is 76’ it has the 76’ ECU. Probably not a safe assumption. Have you ever checked to verify the ECU part number you are running? Those damn assumptions (IMG:style_emoticons/default/headbang.gif) we all do them.

[emerygt350]

I actually have an extra known good 73 ECU you could borrow if we get that far.

Let's get that low vacuum figured first. 2 common easy things will directly result in lower vacuum. Over tight valves. Good to check that, did you do the crusty method when you adjusted them?

Second is timing. Which also plays into that poor startup. We could be looking at a combination of the two.

Glad to see how much of an effect the mps had while it was running.

[emerygt350]

Here is a video of mine at cold start this morning. You can see how the vacuum starts and where it is after a minute and a half. The video starts maybe 5 seconds after I started the car. Didn't think of it till I started otherwise I would have recorded that for you too.
https://www.youtube.com/shorts/-owQvPa68sc
Don't mind the wonky AFR, it takes forever for that thing to kick on.

Here is where all the needles are after my 1 mile commute to work.