85 Hard to start when warmed up
Thread Starter
Safety Car
Joined: Oct 2007
Posts: 4,426
Likes: 229
From: Pennsylvania
85 Hard to start when warmed up
My 1985 starts perfectly every time when cold, but after it is driven awhile, it takes a little longer to start. I just changed the plugs and wires but the problem is still there. It does not miss or run poorly at all. The starter spins the engine quickly, but it takes too long. The car only has 29,000 miles on it, but it still has the original fuel filter. Does anyone think this might be what to change next or is it maybe the original cap and rotor at fault here?
Advanced
Joined: Dec 2007
Posts: 77
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From: O Fallon IL
I would guess that you should start with the fuel filter... original with low miles means its been sittin- I would think that maybe its hard for the cold pump to flow through- then maybe i'd have your fuel pressure tested to see if it reads properly through the rpms to see if your pump is getting weak... I just don't know enough to tell if the cold made that much of a difference on the cap and rotor- I know the battery has to work harder to get the power to the coil when its cold...
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It sounds like leaky fuel injectors to me.
Advanced
Joined: Dec 2007
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From: O Fallon IL
Race Director
Joined: Jun 2005
Posts: 17,640
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From: Lenoir City TN
St. Jude Donor '08-'09-'10-'11
Next hot start hold the gas pedal to the floor, this will make the computer enter flood state. If it starts quickly odds are the injectors are leaking. Check and see how long the fuel lines hold pressure after shutdown, might need to pinch return line.
Intermediate
Joined: Aug 2007
Posts: 28
Likes: 1
From: Crystal Lake Il
If the fuel pressure is low when warm, you may want to take a look at the short hose between the pump and the output tube. The one in my 84 was like a sponge and once the car was warm, it leaned out. I don't know if GM changed the hose once they went to port injection but it is something to think about.
Instructor
Joined: Oct 2007
Posts: 201
Likes: 1
From: NY
I just went through a similar situation with my 1991 coupe, 7500 original miles, completely stock. The car started nice, ran well when cold, but when it warmed up started to shake like mad. When it got hot it stalled, the it would not start till it cooled off.
Bottom line, 2 bad fuel injectors, 2 almost bad fuel injectors. I changed all eight and the car runs like a champ.
I am not a mechanic, but I understand the fuel injectors are easily checked with an ohm meter. Check them when the engine is hot, so you can duplicate the conditions under which the car will not start.
Good luck.
Bottom line, 2 bad fuel injectors, 2 almost bad fuel injectors. I changed all eight and the car runs like a champ.
I am not a mechanic, but I understand the fuel injectors are easily checked with an ohm meter. Check them when the engine is hot, so you can duplicate the conditions under which the car will not start.
Good luck.
Thread Starter
Safety Car
Joined: Oct 2007
Posts: 4,426
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From: Pennsylvania
If it is leaky fuel injectors, should I be getting a code or check engine light? I was getting a check engine light after driving it for a while, and I had it tested . It showed EGR problem. I didn't fix it. The check engine light quit coming on and I never did have any drivabilty problems. Like I said the engine runs beautifully with no issues. It just takes a few extra cranks for it to start when warm. It seems that this problem started when the check engine light quit coming on. When it did come on before, it would reset itself when I shut the car off.
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Le Mans Master
Joined: Sep 2006
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From: Phoenix AZ
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hard start
well, you know it's heat related. let's look at the possibilities:
1. letsee, what's up front that gets hot, sits over the rotor in the distributor that creates spark?
2. warm fuel returning to the gas tank shouldn't affect the fuel pump, but bad bearings in a little used fuel pump could.
3. leaking cold start injector?
4. a heat sensitive fuel pump relay
5. a failed mass air sensor burnoff relay
6. an iffy mas air power relay
7. a bad mas air module found only in an 85
8. bad contacts in an ignition switch
9. none of the above
1. letsee, what's up front that gets hot, sits over the rotor in the distributor that creates spark?
2. warm fuel returning to the gas tank shouldn't affect the fuel pump, but bad bearings in a little used fuel pump could.
3. leaking cold start injector?
4. a heat sensitive fuel pump relay
5. a failed mass air sensor burnoff relay
6. an iffy mas air power relay
7. a bad mas air module found only in an 85
8. bad contacts in an ignition switch
9. none of the above
Le Mans Master
Joined: Oct 2003
Posts: 6,130
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From: seattle WA
To me it sounds like either....a failing fuel pump relay $12-$15. or a leaky injector(s). Next time, when you get into that situation, first just turn the key to the ON position...listen for the fuel pump to run for a couple seconds....if it doesn't then the cause is LIKELY the FP relay, if they fail the oil pressure switch comes into play, but you have to crank the engine until oil pressure reaches 4 pounds before it energizes the fuel pump...sound familiar? IF that doesn't help...the next time, HOLD the gas peddle down while cranking, will throw it into clear flood mode, if it starts easier that way the injectors are suspect.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
I had the same situation on my 86'. Always an easy cold start, and always a hard warm start. Having the injectors serviced fixed the issue for me. I had Rich at Cruzin Performance do the injectors and I was very pleased with him and his work.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
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From: Louisiana
Check the injectors. Ohm them hot and cold and if the fuel pressure drops quickly...do the proper fuel leak down procedure to see where the leak is coming from. Pull the spark plugs and see if any are wet with fuel.
Cruising
Joined: Sep 2006
Posts: 10
Likes: 0
From: Mississauga Ontario
I've got the same problem with my 86. I had my injectors serviced a while ago and it didn't solve the problem. If you're a 'mild-mannered' driver, it could be carbon build up on the valves/stems is absorbing the air/fuel when the engine is hot making it require more of the mixture to get it going when trying to start again. Carbon buildup doesn't absord the mixture as much when the car is cold.
According to the first link I provided below, they say to let the car go (higher RPM) every once in a while to prevent the build up but didn't address the problem if you already have build up. The second link suggested to fill up Chevron Techron plus after every oil change and this should help break the build up down. When it warms up, I plan on trying both out (driving a bit harder and using the Techron)
here are the links:
http://www.zr1netregistry.com/ZR1_tr...g.htm#Cranking
http://www.corvettefever.com/techart...gas/index.html
According to the first link I provided below, they say to let the car go (higher RPM) every once in a while to prevent the build up but didn't address the problem if you already have build up. The second link suggested to fill up Chevron Techron plus after every oil change and this should help break the build up down. When it warms up, I plan on trying both out (driving a bit harder and using the Techron)
here are the links:
http://www.zr1netregistry.com/ZR1_tr...g.htm#Cranking
http://www.corvettefever.com/techart...gas/index.html