Hard starting when engine is cold; not the coils
07-09-11, 07:07 PM
#1
Hard starting when engine is cold; not the coils
I am currently in the middle of diagnosing my starting issues and I'd like some ideas from the almighty ClubLexus. Allow me to provide some background on my 1994 SC400.
Yesterday I tried to start it and it cranks perfectly, but just doesn't fire up and there are gas vapors coming out the exhaust. After about 8 tries, I can tell it is almost about to fire up. By the 12th try, it fires up and spits some smoke but it is gone quickly. It revs fine, but when I let off the throttle, RPMs drop very low (~100) briefly and then go back to normal idle. I shut it off and try to start again. Fired up like a dream.
Changed the ignition coil today and it made no difference at all. Still took at least 10 tries to get it fired up. After it fired up, I shut it down and tried again and it started no problem. Same amount of smoke when I first fired up but it was gone quickly. In park, it revs normally right up to redline, but when I let off, RPMs drop very low, then back to idle. I also drove around and when I went WOT, it upshifts at ~4K RPM which isn't normal at 100% throttle.
4 hours later I try to start again. Same problem starting, but this time it only takes 3 tries to get it fired up. Same symptoms as before.
Possibly relevant: 2 weeks ago I drove to the store with no problem. Came back out after 5 minutes and it started to bog down. Had a hell of a time starting it back up so I could limp home. Seems to bog down and stall whenever I apply more than 15% throttle.
Can anyone help me out please?
Yesterday I tried to start it and it cranks perfectly, but just doesn't fire up and there are gas vapors coming out the exhaust. After about 8 tries, I can tell it is almost about to fire up. By the 12th try, it fires up and spits some smoke but it is gone quickly. It revs fine, but when I let off the throttle, RPMs drop very low (~100) briefly and then go back to normal idle. I shut it off and try to start again. Fired up like a dream.
Changed the ignition coil today and it made no difference at all. Still took at least 10 tries to get it fired up. After it fired up, I shut it down and tried again and it started no problem. Same amount of smoke when I first fired up but it was gone quickly. In park, it revs normally right up to redline, but when I let off, RPMs drop very low, then back to idle. I also drove around and when I went WOT, it upshifts at ~4K RPM which isn't normal at 100% throttle.
4 hours later I try to start again. Same problem starting, but this time it only takes 3 tries to get it fired up. Same symptoms as before.
Possibly relevant: 2 weeks ago I drove to the store with no problem. Came back out after 5 minutes and it started to bog down. Had a hell of a time starting it back up so I could limp home. Seems to bog down and stall whenever I apply more than 15% throttle.
Can anyone help me out please?
07-09-11, 09:52 PM
#2
It sounds like its flooded with fuel. Start by checking for spark when its cold, its very easy. Black smoke means too much fuel. Next I would either check or replace the coolant temp sensor as it plays a major role on fuel delivery, as engine warms up less fuel is needed. Last I would check for a leaking injector/s. You really don't want to keep stressing the starter with 12 cranks every morning because replacing it is not easy.
07-10-11, 09:16 PM
#4
did you replace one coil, or both of them? There are two coils for those cars so you might want to look into the other one. The black smoke is all the extra fuel that was used to initally start it causing excess fuel in the engine and exhaust that gets burned off when it finally starts. Any check engine codes stored?
07-10-11, 11:28 PM
#5
Today I checked a few things, and noticed that there is fuel in the intake. What does that mean?
When it does fire up, I notice that it bogs slightly for a second around 100 RPM and then climbs to normal idling speed. Usually it is just supposed to fire up and idle. Does this give any indication of what the problem might be?
Also checked spark plugs and they are ok. Wires are also ok. Compression is good at 190.
Doesn't seem to be spark, since it eventually starts up. And now it only takes 1 or 2 tries. And it doesn't seem to be the coolant temp sensor because immediately after I start it up successfully, the next time is absolutely perfect. How do I check leaking injectors?
Both coils have been replaced, and there is no CEL.
When it does fire up, I notice that it bogs slightly for a second around 100 RPM and then climbs to normal idling speed. Usually it is just supposed to fire up and idle. Does this give any indication of what the problem might be?
Also checked spark plugs and they are ok. Wires are also ok. Compression is good at 190.
It sounds like its flooded with fuel. Start by checking for spark when its cold, its very easy. Black smoke means too much fuel. Next I would either check or replace the coolant temp sensor as it plays a major role on fuel delivery, as engine warms up less fuel is needed. Last I would check for a leaking injector/s. You really don't want to keep stressing the starter with 12 cranks every morning because replacing it is not easy.
did you replace one coil, or both of them? There are two coils for those cars so you might want to look into the other one. The black smoke is all the extra fuel that was used to initally start it causing excess fuel in the engine and exhaust that gets burned off when it finally starts. Any check engine codes stored?
07-13-11, 09:54 AM
#6
An update, apologies for my lack of proper terminology:
I went to check again on the starting issue and I notice a few peculiarities. With the key in the ON position, the CEL stays on, when normally all dash lights shut off in a few seconds. When I try to start it on the 2nd try, I can hear that it is very close to firing up. It sounds a bit different than free cranking, and alternates between "almost started" and "free-cranking" for a few times. The CEL turns off when these "blips" of "almost started" occur and seems to flash on whenever it's cranking only. Once it is started, the CEL just stays off.
I shut it off, and try again, and it fires up immediately. When I leave the key in ON, the CEL still stays, but shuts off as soon as it fires up.
Also, smoke is coming out the exhaust during idle and it seems more than usual.
Does these clues give any obvious indication to the problem?
I went to check again on the starting issue and I notice a few peculiarities. With the key in the ON position, the CEL stays on, when normally all dash lights shut off in a few seconds. When I try to start it on the 2nd try, I can hear that it is very close to firing up. It sounds a bit different than free cranking, and alternates between "almost started" and "free-cranking" for a few times. The CEL turns off when these "blips" of "almost started" occur and seems to flash on whenever it's cranking only. Once it is started, the CEL just stays off.
I shut it off, and try again, and it fires up immediately. When I leave the key in ON, the CEL still stays, but shuts off as soon as it fires up.
Also, smoke is coming out the exhaust during idle and it seems more than usual.
Does these clues give any obvious indication to the problem?
Last edited by greyBLITZ; 07-13-11 at 10:28 AM.
Thread
Thread Starter
Forum
Replies
Last Post
derekhale
Performance & Maintenance
11
05-23-10 04:17 AM
grindin8o8
Performance & Maintenance
1
03-08-10 06:25 PM
