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Improve cold start time?


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Is it possible to improve cold start cranking time?  The car has new plugs, wires, cap, rotor etc and runs great once its started.  It's also worth noting that after the car has started once, it will start considerably quicker the next key turn (demonstrated on the video).

Video: https://www.youtube.com/watch?v=yiT8P_TLuLM

My old mechanic said it simply does this because the engine "just takes longer to build pressure than other cars."  There are no vacuum leaks (checked with a cigar) but there is oil blowby via either worn piston rings or valve seals (I know that due to there being a small amount of oil on the plugs) but I'm not sure if that could be the reason.

Note: this video was created when it was about 80 degrees out so the cold start injector was not firing.

 

Any ideas?

 

-chase

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Mine does that too. I suspect your fuel check valve on the output side of your fuel pump doesn't hold pressure overnight. It holds for some shorter period of time (seconds, minutes, hours?) but not enough hours for it to have fuel pressure for that first cold start of the day.

To test that theory, you can force your fuel pump to run and build pressure before you try to start the key. Couple different ways to accomplish that depending on the year, but the one failsafe version is to disconnect the small spade connector to the starter solenoid and then turn the key to "START". You should hear the fuel pump run. And I bet you'll be able to hear the difference when the pressure has reached normal.

After you're convinced the pressure is up to where it should be, reconnect the starter and then start the car.

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I’ve just written an essay on this in another thread (post 68) that says pretty much what the Captain is telling you above ...

 

 

https://www.classiczcars.com/forums/topic/63901-delphi-mechanical-fuel-pump-stops-pumping-fuel/

 

Other factors are:

 

TIMING: how much base timing do you have on your distributor? After my first and last service / tune up with a UK z specialist, I found that the base timing was set at 0 degrees!!! OK that is an extreme condition but it took quite a lot of cranking to start and proved the point on base timing!! With the 123 ignition distributor I now have 10 degrees base (adding 5 more at 800rpm) and she fires the instant the fuel arrives. In case you aren’t aware, base timing is the timing of the dizzy before any mechanical advance arrives (i.e. timing at idle, typically I have found 15-17 degrees is ideal). When the revs rise, the dizzy adds a total of 12-15 degrees mech advance to that figure, depending on which one you have.

 

COMPRESSION: if you have a worn engine with low compression, it takes a while cranking to build heat in the cylinder. Have you performed a dry and wet compression test? Anything below 160psi is questionable - ideally you want over that figure. If your wet test PSI jumps up then you have worn rings/bores.

 

A NICE HOT SPARK: do you have a decent coil with a decent distributor and decent HT leads? Are your plug gaps set appropriately? The hotter the coil, the more gap you can run so the bigger the spark (FYI, I run 1.2mm with a 1.5ohm flamethrower coil and 8mm HT leads). While HT leads can look OK, you’d be amazed the difference a new set makes to your engine’s responsiveness.

 

Happy hunting!

 

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6 hours ago, AK260 said:

I’ve just written an essay on this in another thread (post 68) that says pretty much what the Captain is telling you above ...

 

 

https://www.classiczcars.com/forums/topic/63901-delphi-mechanical-fuel-pump-stops-pumping-fuel/

 

Other factors are:

 

TIMING: how much base timing do you have on your distributor? After my first and last service / tune up with a UK z specialist, I found that the base timing was set at 0 degrees!!! OK that is an extreme condition but it took quite a lot of cranking to start and proved the point on base timing!! With the 123 ignition distributor I now have 10 degrees base (adding 5 more at 800rpm) and she fires the instant the fuel arrives. In case you aren’t aware, base timing is the timing of the dizzy before any mechanical advance arrives (i.e. timing at idle, typically I have found 15-17 degrees is ideal). When the revs rise, the dizzy adds a total of 12-15 degrees mech advance to that figure, depending on which one you have.

 

COMPRESSION: if you have a worn engine with low compression, it takes a while cranking to build heat in the cylinder. Have you performed a dry and wet compression test? Anything below 160psi is questionable - ideally you want over that figure. If your wet test PSI jumps up then you have worn rings/bores.

 

A NICE HOT SPARK: do you have a decent coil with a decent distributor and decent HT leads? Are your plug gaps set appropriately? The hotter the coil, the more gap you can run so the bigger the spark (FYI, I run 1.2mm with a 1.5ohm flamethrower coil and 8mm HT leads). While HT leads can look OK, you’d be amazed the difference a new set makes to your engine’s responsiveness.

 

Happy hunting!

 

Thank you so much for these great ideas, I'll tackle them one by one:

Fuel: I tried the pump priming method but that didn't change things.

Timing: I recently changed distributors to a rebuilt one (the old one's center bushing was dying) and with both OEM distributors I get the same result.  The car is also timed at 10 degrees at idle and runs smooth as glass.

Compression: Not sure about the compression (kind of afraid to look haha) but the car runs really well and has great highway pull as-is.

Spark: I changed the plugs last year to the iridium plugs with new ngk leads and all the recommended tune-up brands/gear to no change.  The car also has some sort of ignition box made by "Jacobs electric."  The one spark related issue I can think of is the center terminal on my distributor cap is semi melted - I put some ox-guard on the side of the terminal walls and plug and I believe that helped though.

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