Hot Start Question
Thread Starter
Race Director
Joined: Jun 1999
Posts: 14,924
Likes: 9
From: Merritt Ils Fl
Hot Start Question
Libertyvet posted his 89 would start immediately when cold but required extended cranking when hot. Several members said it was leaking injectors followed by replacement discussion. If a car has leaking injectors, when cold the injectors have had ample time to leak down yet it starts immediately. If hot and the injectors leak down it requires extended cranking. In both cases the fuel pump comes on before the key is turned to the start position repressurizing the injectors. Will someone please explain how leaking injectors will cause different starting conditions based on engine temps. There are parameters in the chip that bear on hot/cold starts but I am too new at this game to begin to explain what they are and/or do. Maybe some of our gurus can enlighten us. Please.
Melting Slicks
Joined: Aug 2003
Posts: 3,377
Likes: 387
From: Lakeville MI
For a cold start, you need lots of enrichment to get enough fuel to vaporize. In this case leaking injectors cold potentially improve the cold start cranking times, at the expense of bad start up emissions.
During a hot start, where little or no extra enrichment is needed, the same leaking injectors would likely cause a flooded condition, making it more difficult to start.
But if its flooded, extended cranking won't really help unless the throttle is also opened in order to help lean things out. Otherwise it will just keep on flooding.
The 89 and later cars require 8 distributor reference pulses during crank before the injectors will fire. I would bet this has something to do with the hard starting when hot. Could be a distributor problem preventing the required # of reference pulses when hot.
During a hot start, where little or no extra enrichment is needed, the same leaking injectors would likely cause a flooded condition, making it more difficult to start.
But if its flooded, extended cranking won't really help unless the throttle is also opened in order to help lean things out. Otherwise it will just keep on flooding.
The 89 and later cars require 8 distributor reference pulses during crank before the injectors will fire. I would bet this has something to do with the hard starting when hot. Could be a distributor problem preventing the required # of reference pulses when hot.
Instructor
Joined: Apr 2003
Posts: 197
Likes: 0
I just put my 89 back on the road after sitting for two years. It would start cold but wouldn't re-start. After having numerous codes thrown out got good feed back in this forum. I had TWO bad injectors, one in each bank. The ECM was cutting fuel off to each bank. Once replaced the injectors (did all 8 since the advice was not "if" the stock injectors go but "when") Car has stop throwing codes out and fires right up.
Don't know if this helps you.
Don't know if this helps you.
Thread Starter
Race Director
Joined: Jun 1999
Posts: 14,924
Likes: 9
From: Merritt Ils Fl
Originally Posted by seenalot
I just put my 89 back on the road after sitting for two years. It would start cold but wouldn't re-start. After having numerous codes thrown out got good feed back in this forum. I had TWO bad injectors, one in each bank. The ECM was cutting fuel off to each bank. Once replaced the injectors (did all 8 since the advice was not "if" the stock injectors go but "when") Car has stop throwing codes out and fires right up.
Don't know if this helps you.
Don't know if this helps you.
At the risk of being **** about this but I can't for the life of me see how injectors alone can cause this problem.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
I agree with tequilaboy. Also the injector coil resistance plays a part too. The coil resistance changes some when it heats up. By ohming the coils, you can tell if the injector is using the ref signal correctly and not flubbing up what the ECM is sending.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
injectors
remember the coolant sensor tells the computer to go into a closed loop configuration.
starting cold, it fires on a lookup table in cold condition.
so hot condition has a temp sensor value, a mat sensor value, a oxygen sensor value.
it is possible for the O2 sensor to pull back the fuel, but when it fires, it will just run lean at idle till the excess fuel is thrown out past the oxygen sensor.
Id look at the coolant sensor , check for high resistance when cold, low resistance when hot. make sure it varies.
it's also possible old plug wires keeps it from starting when hot. or slow to start. cracked dist cap, bad rotor, bad ignition coil, etc.
starting cold, it fires on a lookup table in cold condition.
so hot condition has a temp sensor value, a mat sensor value, a oxygen sensor value.
it is possible for the O2 sensor to pull back the fuel, but when it fires, it will just run lean at idle till the excess fuel is thrown out past the oxygen sensor.
Id look at the coolant sensor , check for high resistance when cold, low resistance when hot. make sure it varies.
it's also possible old plug wires keeps it from starting when hot. or slow to start. cracked dist cap, bad rotor, bad ignition coil, etc.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Originally Posted by coupeguy2001
remember the coolant sensor tells the computer to go into a closed loop configuration.
starting cold, it fires on a lookup table in cold condition.
so hot condition has a temp sensor value, a mat sensor value, a oxygen sensor value.
it is possible for the O2 sensor to pull back the fuel, but when it fires, it will just run lean at idle till the excess fuel is thrown out past the oxygen sensor.
Id look at the coolant sensor , check for high resistance when cold, low resistance when hot. make sure it varies.
it's also possible old plug wires keeps it from starting when hot. or slow to start. cracked dist cap, bad rotor, bad ignition coil, etc.
starting cold, it fires on a lookup table in cold condition.
so hot condition has a temp sensor value, a mat sensor value, a oxygen sensor value.
it is possible for the O2 sensor to pull back the fuel, but when it fires, it will just run lean at idle till the excess fuel is thrown out past the oxygen sensor.
Id look at the coolant sensor , check for high resistance when cold, low resistance when hot. make sure it varies.
it's also possible old plug wires keeps it from starting when hot. or slow to start. cracked dist cap, bad rotor, bad ignition coil, etc.
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Pro
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Originally Posted by tequilaboy
For a cold start, you need lots of enrichment to get enough fuel to vaporize. In this case leaking injectors cold potentially improve the cold start cranking times, at the expense of bad start up emissions.
During a hot start, where little or no extra enrichment is needed, the same leaking injectors would likely cause a flooded condition, making it more difficult to start.
But if its flooded, extended cranking won't really help unless the throttle is also opened in order to help lean things out. Otherwise it will just keep on flooding.
The 89 and later cars require 8 distributor reference pulses during crank before the injectors will fire. I would bet this has something to do with the hard starting when hot. Could be a distributor problem preventing the required # of reference pulses when hot.
During a hot start, where little or no extra enrichment is needed, the same leaking injectors would likely cause a flooded condition, making it more difficult to start.
But if its flooded, extended cranking won't really help unless the throttle is also opened in order to help lean things out. Otherwise it will just keep on flooding.
The 89 and later cars require 8 distributor reference pulses during crank before the injectors will fire. I would bet this has something to do with the hard starting when hot. Could be a distributor problem preventing the required # of reference pulses when hot.
Couldn't have said it better!!
