really hard to start when warm

[brandon2944]

I recently began driving my 87 NA again and noticed that the vehicle will start right up after sitting, but when I try to start it after it has been driven it takes several seconds to fire up. Sometimes I have to give a second try, I don't want to burn up the starter it takes so long. I have replaced the fuel filter, since I hadn't changed it in 2 years, but no difference. The car has only 126k on it and I am pretty sure most parts outside of the cam/balance belts, and water pump are all original so I don't even know where to begin. Thanks Brandon.

[Techno Duck]

Sounds like vapor lock. That could be caused by leaking fuel injectors or a bad fuel pressure regulator. Its allowing excess fuel to be dumped into the cylinders while the car is shut off.

[brandon2944]

Thanks for the info, will try the FPR first and see if that helps. I did notice my car idles a little low (650-700rpm) and worse with the A/C on. But pulls strong to redline with no hiccups, even in 3rd or 4th.

[Razorback1980]

Do you notice any smoke when it does start after it is hard to start. If you are dumping excess fuel into the cylinders, you should see a puff of smoke from the exhaust and it will probably be black in color. Also if you are dumping excess fuel into the cylinders, pushing the accelerator all the way to the floor will help it restart. The accelerator controls how much air goes to the engine and if you have too much fuel, allowing more air will help balance the air/fuel ratio a little better until it starts. Another thing to check...after you have driven it for a while, go pull the vacuum line coming from the FPR and damper to the air control unit and see if there is fuel in there. My 87 had a leaking FPR and it was dumping fuel in the intake manifold when I shut it off and it would be hard to start after it had been started once and brought the fuel pressure back up to the right level. If the car idles low, that is probably a different problem. There is an electronic idle control that may need cleaned or replaced.

[Techno Duck]

Yea, Razorback reminded me of something, if you have other idle problems it could also be related to your ISV (idle stabalizer valve) or DME temp sensor in need or replacement.

[highway]

I've recently had trouble with my crankshaft position sensors. Apparently there are 2, one for the crank and the other for the flywheel or something along those lines. I hope you're not having that problem because they sensors run for around $200 each. Let me tell you it wasn't fun having to tackle that on top of getting my belts/rollers/waterpump done.

[gtroth]

I had to crank mine for ~3 seconds only when warmed up until I changed my FPR. Now starts right up warm or cold. If you can, measure your fuel pressure and fuel pressure leakdown. My pressure was way high and my leakdown way fast.

[uvachief]

I am having a similar problem. Replaced injectors, fuel pressure regulator and filter. Fires up cold. Struggles on a quick warm restart. Cross reference ignition sensors also replaced. Fuel pump?

[John_AZ]

Could be as simple revving or letting it cool down after a hard run---(Thanks Ernie)

Interesting

I know you've done a huge amount of work on the car so I skip vapor lock.

Look at the AFM and make sure the door swings easy and the connection clean.

It could also be the gap on the reference sensors.

GL
John

[968 GUY]

Also, check the fuel pump check valve. The only way to really check it is to remove it,and then you may as well replace it.

[uvachief]

Do you have to adjust the cross reference/speed reference sensors from time to time? Someone suggested checking the connector and mabe crimping it slightly to make sure it has a tight fit at the plug. I may also need to pull it and make sure that 0.8mm gap didn't get corrupted during the top end engine rebuild.

[gtroth]

Can you measure your fuel pressure leakdown?

[gordonmacwillia]

What I noticed about my hot start problem is that it only occurs when the weather is hot in addition to the engine being hot (I live in Florida) and it coincidentally started happening immediately after having had the vehicle serviced. The service tech suspects that the problem is the fuel pump check valve, however I do not see how hot weather can affect this. The fuel pressure port broke off of the fuel distribution manifold prior to my purchasing the car, and the outlet has been sealed. I would appreciate any thoughts. Thanks!

Currently:
1987 944S 16 years
1996 993 4 years

Previously:
1986 911 21 years
1983 911SC 24 years
1969 911T 1 year (blown engine)

1976 TR7 8 years
1976 280Z 20 years
1971 240Z 4 years (stolen)

[gordonmacwillia]

I bought this vehicle 16 years ago and prior to my ownership (as mentioned above), someone torqued off the inspection port (did not use two wrenches?). Rather than re-welding the inspection port back onto the rail, a nut was welded on instead, accompanied by a carburetor washer and bolt. Needless to say, further pressure measurement at the fuel rail (and therefore troubleshooting any fuel delivery problems) was unlikely.

The dealer replaced the check valve to no avail of the hot start problem (they said that they could measure the pressure near the fuel pump and it was leaking down).

The hot start problem eventually became a cold start problem over a months time. I purchased a fuel rail / dampener / fuel regulator assembly from eBay for a delivered price of $75 (I figured that I would at least get an inspection port for the money). My replacement of the assembly solved the problem so either the back pressure regulator or the dampener was leaking.

[JAXTURBO]

Originally Posted by 968 GUY

Also, check the fuel pump check valve. The only way to really check it is to remove it,and then you may as well replace it.

+1... this is what fixed my hard hot start problem. Like 968_GUY said, no checkiing, just replace it. I went 1 step further. Since pump was out and was 20+ yrs old, I replaced pump/check valve.

Warning - that rubber sleeve the pump is in was a b*tch to remove and install on the new pump.

[otto_kretschmer]

I had the same problem earlier this year

when I bought the car the previous owner had a hard start when warm condition and he bought a new fuel pressure damper but never put it in,

so after exausting everything else (electrical related, I thought) I put it in and the car fired right up and has never been a problem since

Pelican Parts - Product Information: 944-110-201-03-M14

my symptoms were:

car starts easily when cold but hard when hot

I suspect the old fuel pressure damper was letting fuel leak past so I had a low fuel pressure when hot

its a $90 part so thats an expensive part to buy on just a hunch

good luck