C4inLA

In your pic of plastic intake version, the vacuum line is laying just above the w/b check valve , correct? So, if running for short time while detached, if any visible fuel coming from end of vacuum line, PR is faulty?

I've had warm start issue for some time as well... I've tapped the pedal once, turned it over a bit longer and it starts? IMHO, this is a frequent Owner complaint and wonder how many accept as normal? I have a vacuum gauge l've been wanting to hook inline to the system and take measurements at different Idle, 1k, 2k, etc... Anybody know what to expect as normal vs abnormal?

Rooting for you to solve the infamous "warm start issue" Sadly, it even has it's own name.

BTW, great pic. Do you live in the countryside? What are the objects on the hillside, is it a cemetery?

John McM

Yes FPR is definitely faulty if gas comes out of the vacuum line. My car has metal intakes so the plastic pic is from someone else. I hope it's accurate. I'm determined to fix this problem and will report back.

I don't live in the Country but have easy access. This particular image was taken at a church we visited that I had wanted to see because an ancestor designed and built it in 1863.

Navaros911

You can unhook the vacuum line at the bottom (FPR side) without removing anything, provided someone with small hands does it.

May have said this before... A few threads with this issue lately.

John McM

I chipped my windscreen on a B road run so the car went in for a new screen $$$$$.

While it was in there I asked the shop to check the fuel pressure. It turned out to be absolutely solid, cold, warm and hot. This means that the injectors have fuel pressure on start up no matter what the temp. The shop thinks it could be my aftermarket ECU. As a test I am going to change back to the OE ECU and see what happens.

BTW: I found that a hot start was not a problem if the key was advanced to ignition on for a few seconds before starting. Not sure why it would do that.

robt964

^ on that subject...

One trait I notice of this ECU is that the engine will not fire UNTIL the initial pump prime has completed. This is not due to lack of fuel pressure, but appears to be more about how it works. This means once you turn the ignition on, you have to wait a few secs before turning the engine. As our cars have a pressure non-return valve at the pump outlet, this priming is of less importance. The pump priming duration is tweakable in the config. I turned mine right down to about 1 second. This is fine to do. Put it this way - the motronic doesn't prime the system. It only energises the pump once it sees the engine turning/cranking.

John McM

Thanks Rob, I will adjust this. As you know the 964 requires a non start to go back to the fully off position before going through the start sequence again.

If the car stalls at say an intersection (happens rarely but the car still isn't perfect), then there's a mad rush to turn the ignition off and attempt to restart. It's frustrating and embarrassing to be cranking for seconds until it catches.

It's great if this is as simple as reducing a variable on the ECU, but as I've said before I think this kit is either under-documented or just not intended for the average DIY mechanic. It was touted as plug and play but it hasn't turned out that way.

robt964

No map supplied with an ECU will cover all bases for everybody. They ALL require tinkering to get them how you like it. The level of investment and dyno time the original Motronic would have received is incomparable.

John McM

The WB sensor is wired in. It's too late to start it up now so will do that tomorrow. Quite excited to see a live AFR and finally start to understand what level the overfuelling is at right now.

John McM

Lambda turned out to be near perfect as is. A local mechanic suggested I run a tank of race fuel and see if it cleaned up the exhaust. It sure did! Based on the readings and reaction to different fuels I am leaving the map as is, but adjusting the fuel pump prime time lower (it delays the ECU allowing it to start) to aid with warm starts.

John McM

With the test run done I have moved on to the alternator. It sounded a bit rumbly and it was the last weak link in my refurb. It may well have lasted a few more years but I want a longer base line so I farmed it out to a local enthusiast.

The brushes will be replaced (didn't know you could do this without replacing the rectifier as well so thats a win). The two bearings are being changed and the slip ring smoothed.

The large bearing was on the way out apparently so this is cheap insurance when you have an expensive new fan at risk.

robt964

Good news about your map John I didn't think it could be far off considering you're running a stock engine.

John McM

Yes, it is good news. I watched the Lambda live and it showed nothing out of the ordinary. Running around town I was getting 0.95 to 1.0. It dropped when I pushed it but that's exactly what I wanted. In hindsight maybe taking out the cat wasn't the brightest move but that's 20/20 hindsight.

John McM

Alternator recondition is finished. Two new bearings, slip rings smoothed back to round (it will need new rings next time) and a new rectifier/brush set.

John McM

Alternator refitted. A short test drive to pick up 4 litres of Mobil 1 Racing oil and all seems good. I washed the car and put it under a cover. The next drive will be an 1,800km road trip completed over two weekends. A solely air cooled affair. A '70T, 1990 C2, 1990 C4 and 1991 T3.3

John McM

And as one refurb closes another one opens! I have purchased a second 1990 964 C4. This one has a large mileage (for New Zealand) of 237,000 km (147,000 miles). It doesn't smoke or have a graunching gearbox however there is evidence of a past water leak in the cabin and deferred maintenance e.g. Crazed indicators, split CV boots, perished ARB bushes and strut bump stops etc.

I will do a full interior change to Black (currently Linen), a full service, check the planetary gear etc. Purchase cost was USD 34,000/GBP 23,600/ AUD 46,700.

As the mileage is highish I don't have a large budget for refurbishment given New Zealand 964 prices. The goal is to get it to enthusiast condition then pass it on to an enthusiast. Even If that takes a couple of years I will be happy. No rush as the joy is in tinkering not in buying and selling.