Hard starting when warm, 10-15 min/ stop 10 min/ hard to start Options

[Tom]

Thanks for the replys.
Don't think the ignition switch is bad. The hard to stsrt issue comes into play after sitting for 10-15 minutes. Since the switch is in the passenger comp, it should cool rather quicky. I am using logical trouble shooting methods here and maybe that is part of the problem. I rebuilt the ignition harness using new teflon coated wire and all new connectors, so I'm pretty sure that isn't the problem. I guess the next step is to take some voltage readings while starting cold and then more when the hard to start problem is there and compare the readings. I'll post the findings when I have them.
Not the cold start valve as I have the pressure gage hooked up there now.
I'm surprised that this doesn't have a more widely known cure since it has been around since the cars were new?
Tom

[pbanders]

News flash, guys. THEY DID THIS WHEN THEY WERE NEW!

The Cap'n

As the Cap'n says, this is "normal" behavior. Mine does the same thing, though not as bad as described here. It's a flaw in the system design. The head cools off more rapidly than the rest of the engine, so the head temp sensor gets "cold" even after only 10 minutes. However, the core of the engine is still quite hot. The net result is you get too rich a mixture and it makes starting hard, and the first few minutes of running are too rich until the heads heat back up. If you let it sit for a full hour, the whole engine gets cold and that's why it starts fine. Mystery solved.

One way to start it more effectively is to open the throttle completely BEFORE turning the key. If you open the throttle once you turn the key, you pump 20 ms worth of gas into two of the cylinders due to the action of the throttle switch, making it even richer. Try that next time and see if it starts faster.

[Tom]

Thanks for the answer Brad. The times I had this happen, I got it to start by fully opening the throttle. Next time I.ll try fully open before trying to start.
Tom

[Jacob]

Since it happens warm, have you tried to check the resistance of the temp sensor? I believe it is supposed to be 20000 ohms when cold and under 300 ohms at operating temp. If the temp sensor is ok and the FI is working as designed then the engine is not getting a rich fuel mix on startup as it does when it is cold. Have you checked your vacuum lines? A vacuum leak could leave you with a too lean mixture. Of course, it should also leave you with a high idle which you are NOT getting.

Do you have a vacuum gauge?

You wrote that you do not get black smoke when it does start, maybe it is too lean.
You also wrote "I've pulled the plugs after cranking and not firing and they are not soaked. " Are the plugs at least a little wet? (IMG:style_emoticons/default/confused24.gif)

Hope this is of some help. (IMG:style_emoticons/default/smile.gif)

[pbanders]

Since it happens warm, have you tried to check the resistance of the temp sensor? I believe it is supposed to be 20000 ohms when cold and under 300 ohms at operating temp. If the temp sensor is ok and the FI is working as designed then the engine is not getting a rich fuel mix on startup as it does when it is cold. Have you checked your vacuum lines? A vacuum leak could leave you with a too lean mixture. Of course, it should also leave you with a high idle which you are NOT getting.

Do you have a vacuum gauge?

You wrote that you do not get black smoke when it does start, maybe it is too lean.
You also wrote "I've pulled the plugs after cranking and not firing and they are not soaked. " Are the plugs at least a little wet? (IMG:style_emoticons/default/confused24.gif)

Hope this is of some help. (IMG:style_emoticons/default/smile.gif)

The CHT is about 3K ohms when at 70 deg. F, and under 50 ohms at operating temperature. See my comments above, the issue is that the heads cool off much more quickly than the cast iron cylinders and pistons, leading to rich starting mixtures after 10-15 min of sitting. You know it's rich because you can get it to start by giving it more air (i.e. opening the throttle). BTW, in D-Jet, vacuum leaks in the intake system do not lead to lean running, as it's a speed-density system. AFM systems (e.g. L-Jet) go lean under vacuum leaks. The lack of black smoke is because when this problem happens, the engine isn't flooded, simply getting too rich a mixture.

[Tom]

Brad,s answer makes perfect sense to me. As soon as it warms up some here in the PNW, I''l put this to the test and let you all know what the results are.
Tom

[914pwr]

Tom,

Any resolution on your issue? I've had the Exact same issue on my '75 2.0 and have been in the habit of holding the pedal to the floor to get it to start. I understand the theory about the heads cooling faster, but the car didn't seem to have this problem many years ago.

I have a new CHT sensor and it didn't seem to help.

Tim

[Tom]

Well, it is a year later and I only had this happen once this summer, but I haven't been driving the car much as my back has been giving me grief. I used the "pedal down before starting" the one time it didn't want to fire and it started much faster. I usually just have to turn the key to start with no throttle applied to get this car to start up and then it idles OK. When this doesn't get the car to start, I turn the key to off, press pedal to the floor, then try starting again. Started up in less than 10 seconds.
Tom

[jim_hoyland]

Can the resistance from the CHT be lowered to correct for the temperature differences ?

[mburkhart]

I experienced almost the similar symptoms this summer in my 74 2.0L, although my car actually stalled and then wouldn't start. Car has always started and idled strongly when cold. I've been told it's vapor lock, and I've been told vapor lock is a myth (Fuel pump is in the stock position for a 74). I don't care what it is, but I'd sure love to be able to trust my car again. I did look in my gas tank and found some rust at the bottom but it didn't look like enough to clog the fuel screen or a fuel filter. Here's what my experience was (this all happened on one day):

1) Drove about 15 miles then parked the car for 1.5 hours. Car wouldn't start. Tried intermittently for 10-15 minutes until I finally held down the pedal for 30-45 seconds (at least) and the car finally started.

2) Drove about 3 miles to the store and parked the car for 5-10 minutes. Car wouldn't start. Tried intermittently for 15-20 minutes until I finally held down the pedal for 30-45 seconds (at least) and the car finally started.

3) Drove about 15 miles and the car stalled on the highway. I was downshifting from 4th to 3rd when the car stalled (slow traffic + going up a hill). Car wouldn't start. Tried intermittently for 20-30 minutes until I finally held down the pedal for 30-45 seconds (at least) and the car finally started.

4) Drove another mile and the car stalled down the street from my house. I was downshifting from 3rd to 2nd (turning onto my street). Car wouldn't start. Left it parked for a few hours and then it started right up.

[Garland]

1972 FI
Heres my story:

Starts fine cold. After warmed up, won't start, seems flooded. More so hot weather.

To start, I pull the pump relay and crank it over two times. Each time it will start and run 2 to 5 sec, with out the relay plugged in!. I think this is clearing out the fuel.

Plug in the relay, crank and depress the pedal slightly right after turning the key....fires right up! If not replete, sometimes 3-4 times.

This only happens on hot soak. This has gotten much worst. Every time I drive the car I must now do this for it to start. Unless restarting within 1 to 3 min.

Never had this concern for years, then all of a sudden. Swapped out many items, no solution. HELP please if you can.

Thanks