1977 911s cannot warm start

[wowly]

Hello everyone,

I am new to forum but I have been reading here for a while.

I have a 1977 911s and it's my semi-daily driver now. Recently I ran into warm start issue. When I cold start in the morning, all fine. After a day of work, while still warm ambient, I was able to start but after about 30 seconds, then engine cuts off. When I tried to restart, it just cranked. Left the car overnight in the lot, next morning, everything is fine. No stall on the road.

I plan to do the CIS pressure test this weekend.

Before I do it, anyone might know the cause of the issue?

Thanks in advance!

Oliver
1977 911S 150K+miles

[Joe Bob]

Likely the check valve in the neck of the fuel pump needs to be replaced. Cheap fix.

Easy to start if you spray some ether into the the intake until you replace it.

[7783911]

if check valve is ok, check your fuel accumulator...easy to do a basic test...take off, clean and blow into top to see if air comes out bottom, if it does your rubber diaphragm is failing and not maintaining fuel pressure. i may have a good accumulator for sale if you do need. Check valve is tested with fuel pressure testing to see if pressure is lost over time..well documented in pp, see a thread i started on accumulator in technical forum

[BoxsterGT]

A word of caution.....

With a 77 911 model you likely have the original "side outlet" Fuel Pump & Check Valve.

Relatively speaking, a replacement check valve is not expensive at around $50 from our host.

However the Fuel Pump, if needed is VERY expensive, and if you buy a new check valve and then need a new pump, you are locked in to the new original pump from Porsche or our host at over $800.

I recommend you consider the later Bosch "flow-through" pump at about $125 from our host.

This includes a new Check Valve and with a change in the Feed Hose to the Tunnel this is an easy upgrade.

I am happy to help if needed.

len.cummings @ verizon.net

[wowly]

Thanks for all the great feedback everyone!

@BoxsterGT, with regard to the fuel pump you referred to, do you have the link?

[kach22i]

Originally Posted by BoxsterGT

.....However the Fuel Pump, if needed is VERY expensive, and if you buy a new check valve and then need a new pump, you are locked in to the new original pump from Porsche or our host at over $800.

Wow, 15 years ago they were only about $200.

I'm developing a warm start issue, pretty sure it's a CIS leak somewhere.

[BoxsterGT]

I have replied to "wowly" and hope to be of help.

Since my last purchase of the Bosch "Flow-Through" Pump they have gone up a bit.

Our host has them for $200, though they also offer one from Dansk for about $100, and this sounds like a good deal.

One thing to be aware of is the OD of the check valve.

The early CIS had a 10mm check valve, while all later ones are 12mm. The check valves are interchangeable, so a simple swap will get you going if you have this mis-match.

Don't forget the (2) Copper Crush Rings.

I also offer replacement front Tunnel HOSES....



as a temporary repair, in case this is part of the problem you are having.

For info, please email me. PLEASE, NO pm's, box is usually full.

len.cummings @ verizon.net

[drtyler]

What’s wrong with the Pierburg replacement pump? It is much less expensive than the Porsche pump and mounts in the rear as original.

Originally Posted by BoxsterGT

A word of caution.....

With a 77 911 model you likely have the original "side outlet" Fuel Pump & Check Valve.

Relatively speaking, a replacement check valve is not expensive at around $50 from our host.

However the Fuel Pump, if needed is VERY expensive, and if you buy a new check valve and then need a new pump, you are locked in to the new original pump from Porsche or our host at over $800.

I recommend you consider the later Bosch "flow-through" pump at about $125 from our host.

This includes a new Check Valve and with a change in the Feed Hose to the Tunnel this is an easy upgrade.

I am happy to help if needed.

len.cummings @ verizon.net

[BoxsterGT]

drtyler-

I have not compared the cost of a Pierburg pump with the original "side-outlet" Bosch, but it's a good suggestion.

This particular application by wowly is for a 77 with the Pump mounted up front. The Pierburg Pump may very well work here too.

As for the earlier 73-75 CIS models with their rear pump, this "flow-through" Bosch pump can also be used here....



You can do this by upgrading the Feed Hose from Pump to Accumulator.

Len

[drtyler]

My apologies Len, I thought the 77 was like 73-75 with rear mounted pump.

Originally Posted by BoxsterGT

drtyler-

I have not compared the cost of a Pierburg pump with the original "side-outlet" Bosch, but it's a good suggestion.

This particular application by wowly is for a 77 with the Pump mounted up front. The Pierburg Pump may very well work here too.

As for the earlier 73-75 CIS models with their rear pump, this "flow-through" Bosch pump can also be used here....



You can do this by upgrading the Feed Hose from Pump to Accumulator.

Len

[BoxsterGT]

No need for apology drt, it's a good suggestion.

The side out pump is just too costly when alternatives are out there.

Foe the early CIS (73-74) models, the new hose routing eliminates (4) hose clamps on the Feed Line from pump to accumulator.

The original runs through the Frame rail and clamps are inadequate for the high pressures of CIS.

The factory got it right by model year 1975.

Len

[wowly]

I believe the issue is with accumulator.
@7783911, kindly advise how you sell. I assume it's the same one in the attached picture.

[7783911]

pm sent

[wowly]

Just some updates and experience to share. I changed the fuel accumulator but it was not the cause of the issue. Then I quickly sent the car to the local shop.

It stayed there for a month. The following parts were replaced: FP check valve, CDI, cold start valve and all fuel injectors. Although the bill is painful, I am glad I let the shop look into it. Now she runs like a champ.

[boyt911sc]

Originally Posted by wowly

Just some updates and experience to share. I changed the fuel accumulator but it was not the cause of the issue. Then I quickly sent the car to the local shop.

It stayed there for a month. The following parts were replaced: FP check valve, CDI, cold start valve and all fuel injectors. Although the bill is painful, I am glad I let the shop look into it. Now she runs like a champ.

wowly,

Why did you replace the fuel accumulator if it was not the problem? A simple test will verify if the fuel accumulator is good or bad. Why the shop replaced all these CIS components? Were they all tested to be bad and defective? How many man-hours did you pay for this job?

Tony

[wowly]

Fuel accumulator was a self effort. I tried my luck but it wasn't the cause of it.

The shop charged me 6 hours labor which is reasonable. They started with check valve. Then warm start issue went away. But cold start acted up (in fact, cold start issue was on and off for a while). They did pressure test. I guess the car is old. I was surprised on these many parts changed on one visit. Reasons for changing:
CDI: the old unit was not supplying right voltage
Cold start valve: no fuel observed when car started cold. I was told fuel should be seen through the popup valve in the air box
Fuel injectors: after replacing CDI and cold start value, shop tested all fuel injectors and there were dripping.

Hope this helps others.