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View Full Version : UPDATE 5/03 on Pg 4 Cold start-crap idle/Warm start-great idle



thunderkid84
04-16-2009, 12:22 AM
been having this problem for a minute now. just getting around to fixing it.

so you know how when you first start the car it will kick up the idle and hold for awhile and then idle down ? mine doesnt do that. it fires up and about 2 secs later it will start sputtering and shaking, wanting to die. vacuum will be anywhere between 15-10. after i rev it for maybe 10 secs it will idle on its own but while driving i can smell gas.

now when its warmed up i can fire it up and it idles perfect. vacuum is at 18-20. and i dont smell gas anymore.

i wouldn't think its a vacuum leak otherwise it would idle like crap all the time. could it be the computer dumping too much fuel in, flooding the engine ? i was thinking the cam sensor may be the culprit.

what do you guys think ?

QuickMustang
04-16-2009, 12:11 PM
My first guess would be Engine coolant temperature sensor. does it have a check engine light? Any codes?

275hptbirdsc
04-16-2009, 12:18 PM
Im gonna stick around on this thread this almost sounds like my car sometimes.

thunderkid84
04-16-2009, 01:20 PM
no CEL.

i can try and pull codes.

thunderkid84
04-16-2009, 02:37 PM
ok, warmed up the car like im supposed to. pulled KOEO codes and it gave me a 15 with a continuous memory code of 51.

i ran the test 3 times and everytime it gave the same "51" for continuous memory. but it also gave me 87 and 88 codes for KOEO, but only the first 2 times i ran the test.

QuickMustang
04-16-2009, 06:26 PM
51 is coolant temperature sensor circuit open. Is your coolant temp sensor even plugged in? If it is, I would try to replace the sensor and see if it clears up.


How is your wiring harness condition? It seems like all your codes are circuit problems that may be caused by a messed up wiring harness...Just a thought....

thunderkid84
04-16-2009, 07:38 PM
well i bought a new ECT sensor so i'll see if that works.

i just did a headgasket job in summer 2007 and all the wiring looked good.

QuickMustang
04-16-2009, 09:15 PM
Well, let us know if it fixes it...And if it clears the code...

thunderkid84
04-17-2009, 08:37 PM
i had to pull one of my ex manifolds off to replace the studs and fix a nice leak. i'll be putting it back together tomorrow, then we'll see if that sensor helped out.

thunderkid84
04-22-2009, 10:14 PM
it doesnt seem like it fixed the problem. still runs like crap after a cold start.

do i have to erase the stored memory codes for it to work right ?

QuickMustang
04-23-2009, 09:26 PM
it doesnt seem like it fixed the problem. still runs like crap after a cold start.

do i have to erase the stored memory codes for it to work right ?

Hmmm...You shouldn't have to clear the codes...But it wouldn't be a bad idea, so you can see if you still get the same codes. Are you sure you replaced the right sensor. The ECT sensor is on the passenger side of the engine. The coollant temp sensor on the drivers side just sends a signal to the guage...

fturner
04-23-2009, 09:41 PM
it doesnt seem like it fixed the problem. still runs like crap after a cold start.

do i have to erase the stored memory codes for it to work right ?

You should always disconnect the battery when working with the sensors etc in the car. It'll clear adaptive memory and any codes that are stored so your starting with a blank slate when you startup.

Fraser

thunderkid84
04-23-2009, 09:53 PM
oh trust me, i know i replaced the right one.

think i'll check for more codes tomorrow.

thunderkid84
04-23-2009, 09:59 PM
You should always disconnect the battery when working with the sensors etc in the car. It'll clear adaptive memory and any codes that are stored so your starting with a blank slate when you startup.

Fraser

i did disconnect the battery. i just wanted to know if i have to erase the codes to get rid of the problems

thunderkid84
04-27-2009, 11:58 AM
thought i might mention this...

i have a pressure gauge on the fuel rail and after i cut the engine off the pressure will drop straight to zero before i can even run out of the car and look at it.

i have a 255 lph pump, 50#injectors, and the stock regulator.

is there something wrong here ?

Young-SC-Owner
04-27-2009, 01:11 PM
thought i might mention this...

i have a pressure gauge on the fuel rail and after i cut the engine off the pressure will drop straight to zero before i can even run out of the car and look at it.

i have a 255 lph pump, 50#injectors, and the stock regulator.

is there something wrong here ?

Yes, there is....it should hold pressure.

Leaky or stuck open injector

thunderkid84
04-27-2009, 02:22 PM
is there a way to check each injector besides pulling everything off down to the rail ?

David Neibert
04-27-2009, 02:31 PM
is there a way to check each injector besides pulling everything off down to the rail ?

Start by removing the vacuum/boost refrence hose from the fuel pressure regulator and see if fuel is leaking into the manifold from the regulator.

David

thunderkid84
04-27-2009, 02:36 PM
Start by removing the vacuum/boost refrence hose from the fuel pressure regulator and see if fuel is leaking into the manifold from the regulator.

David

would i pull it off the regulator or where it goes into the return plenum ?

engine running or not ?

will fuel drip out of the hose if the regulator is bad ?

David Neibert
04-27-2009, 04:01 PM
would i pull it off the regulator or where it goes into the return plenum ?

engine running or not ?

will fuel drip out of the hose if the regulator is bad ?

Remove which ever end of the hose is easiest to reach. Don't want the engine running and risk a fire...just turn the ignition on, but don't start the motor. If it's leaking you'll see it and smell it.

Yes..the regulator could be bad and leaking from the port where the vacuum hose attaches. If it's dripping fuel then replace the regulator. If it's not then you probably have an injector that's stuck open.

I had this happen on my 91 SC several years ago, but mine only dropped to 20 psi when the pump stopped. I actually drove it that way for nearly a year before I figured out what was wrong.

David

thunderkid84
04-27-2009, 04:16 PM
thanks dave, i'll check that stuff out tomorrow.

thunderkid84
04-27-2009, 04:57 PM
after reading some old threads i think its either a fully stuck open injector or a bad regulator. leaky injectors seemed to bleed off pressure slowly, whereas my pressure drops to zero immediately.

im told my injectors were bought brand new in a group buy here, maybe 4 years ago, and never installed. i believe it cuz they looked brand new. no nicks in the paint or anything.

so im leaning more towards the regulator which i'll check tomorrow.

David Neibert
04-27-2009, 05:59 PM
When considering the small volume of fuel trapped between the pump and the regulator along with the fact that fuel is not compressable, it doesn't take much of a leak for the pressure to fall off dramatically.

Don't rule out the injectors just because they are nearly new.

David

QuickMustang
04-27-2009, 10:19 PM
I had a friend have a check valve in a fuel pump go bad that caused very similiar symptoms. The car wasn't an SC though, so I don't know..I would think if you had a leaky injector the warm start would be hard/impossible. I would say it's more likely that the fuel is just dumping back in to your tank so at cold start you are running lean. With a warm start, the lean condition wouldn't make as much as a difference...

thunderkid84
04-27-2009, 10:50 PM
yea i still find it wierd that warm starts are fine.

thunderkid84
04-28-2009, 01:57 PM
ok i pulled the hose off from the regulator to the return plenum and primed the pump a few times and nothing cam out.

is my next step is pulling the fuel rail off and checking each injector ?

QuickMustang
04-28-2009, 02:29 PM
OK, this might not be the smartest thing to do since it might foul your plugs if you have a badly leaking injector, but its worth a shot. If your fuel leaks down so fast that it's at 0 by the time you get under the hood, you can:

Warm up your car by normal driving.

Turn key on to prime fuel system (don't start engine), then turn the key off

Repeat previous step about 10 times

Try to start the car

If a fuel injector is leaking, I would think the car would be flooded pretty badly. It probably won't start, and if it does you will have a big black puff of smoke out the exhaust. If it starts how it normally starts with the car warm, then the fuel is just leaking back to the tank.

thunderkid84
04-28-2009, 03:34 PM
if its leaking back into the tank, is it most likely the check valve in the pump ?

is the only cure a new pump ?

thunderkid84
04-29-2009, 01:36 AM
also i still smell gas while im driving so im thinking its more up front than back in the tank.

i'll be pulling everything off to check the actual injectors this weekend. gotta tackle this problem before i hit the track on the 16th.

unless someone knows of an easier way ? :rolleyes:

David Neibert
04-29-2009, 01:18 PM
also i still smell gas while im driving so im thinking its more up front than back in the tank.

i'll be pulling everything off to check the actual injectors this weekend. gotta tackle this problem before i hit the track on the 16th.

unless someone knows of an easier way ? :rolleyes:

I'd give what Jared suggested a try before removing the fuel rail.

David

thunderkid84
04-29-2009, 03:10 PM
dave,

how does the car start fine with it warmed up ?

David Neibert
04-29-2009, 03:44 PM
dave,

how does the car start fine with it warmed up ?

I don't know...mine started fine when it was warmed up too. Probably because the cold start tables are considerably richer.

David

QuickMustang
04-29-2009, 03:48 PM
dave,

how does the car start fine with it warmed up ?

Because when it's warm, you can get away with not having enough fuel. A cold engine running lean will barely run. A warm engine running lean will just tend to run hot...

Are you smelling excess fuel in the exhaust, or are you smelling raw fuel like it's leaking somewhere...

QuickMustang
04-29-2009, 03:54 PM
dave,

how does the car start fine with it warmed up ?

Because when it's warm, you can get away with not having enough fuel. A cold engine running lean will barely run. A warm engine running lean will just tend to run hot...

Are you smelling excess fuel in the exhaust, or are you smelling raw fuel like it's leaking somewhere...

thunderkid84
04-29-2009, 05:06 PM
i dont smell any excess fuel in the exhaust, i smell it while im driving around. mostly after first start-up but i still smell it a little afterwards.

i tried what Jared said and primed it about 4-5 times. it cranked for a little til i put the pedal down some then it turned over. but it would rev up and come down to about 800 then start running like it had a vacuum leak and vacuum would show close to 10 rather than the 18-20 it shows idling good.

should i try some good inector cleaner ?

David Neibert
04-29-2009, 05:39 PM
i dont smell any excess fuel in the exhaust, i smell it while im driving around. mostly after first start-up but i still smell it a little afterwards.

i tried what Jared said and primed it about 4-5 times. it cranked for a little til i put the pedal down some then it turned over. but it would rev up and come down to about 800 then start running like it had a vacuum leak and vacuum would show close to 10 rather than the 18-20 it shows idling good.

should i try some good inector cleaner ?

If this was on a warm motor, then it sounds like an injector is leaking. I don't have enough experince with injector cleaner to comment.

David

thunderkid84
04-29-2009, 06:20 PM
If this was on a warm motor, then it sounds like an injector is leaking. I don't have enough experince with injector cleaner to comment.

David

i tried what jared said to do on a completely cold motor

QuickMustang
04-29-2009, 09:31 PM
i tried what jared said to do on a completely cold motor

Except the first thing I said to do was warm up your motor. But if doing this made your car really hard to start until you held the throttle down, it still probably shows you have a bad injector. You could try some good injector cleaner, I personally like Seafoam or Lucas, but if your injector is that bad, you are really probably wasting your time. You probably either need a new injector or to have them professionally cleaned and tested off of the car..

thunderkid84
04-29-2009, 10:13 PM
yea u did say warm the car up first.

i'll try it when i get home tonite and report back.

i hope it is something as easy as a fual injector. i just wanna get this over with before track time.

thunderkid84
04-30-2009, 12:18 AM
ok, took a nice 15 minute drive home from work. cut it off, primed the pump about 6 times and started it. started right up and (although it was dark outside) i didnt see any smoke out the tail pipes. idle was smooth sitting at 800rpm and vacuum between 18-20.

so........ bad injector or check valve in the pump ?

David Neibert
04-30-2009, 11:27 AM
ok, took a nice 15 minute drive home from work. cut it off, primed the pump about 6 times and started it. started right up and (although it was dark outside) i didnt see any smoke out the tail pipes. idle was smooth sitting at 800rpm and vacuum between 18-20.

so........ bad injector or check valve in the pump ?

If it was a bad injector it sould have been missing on one cylinder. Most likely the check valve, which doesn't really explain your cold start issues.

David

pablon2
04-30-2009, 12:18 PM
It might help to research what changes occur in the system in general in open vs. closed loop. I don't know so I cannot help there, but am just offering another troubleshooting approach.

Also, how old are the O2 sensors? Have they seen coolant? When was your fuel filter last changed? MAF wire last cleaned?

QuickMustang
04-30-2009, 12:51 PM
My theory would be the check valve. I'm guessing that with cold starts it sits long enough that you actually get air in the gas line, so it runs lean/erratic until the air makes it through the line. Cold start will be in open loop for about 30 seconds, so the car wouldn't know that it was running that lean...I think the car runs in open loop for a little bit when it's warm too though. But if the gas didn't have time to completely run out of the line in that amount of time it would still run fine.

It's just my theory though and could be wrong. It kind of confuses me that you had to put the pedal to the floor to get it to start when you primed the pump with it cold...To me, that makes me think injector is more likely....Hmmm...It's a head scratcher...

thunderkid84
04-30-2009, 02:44 PM
Hmmm...It's a head scratcher...

it sure is.

now if its the check valve does the fuel pump have to come out ? and what has to be replaced ?

thunderkid84
04-30-2009, 08:32 PM
If it was a bad injector it sould have been missing on one cylinder. Most likely the check valve, which doesn't really explain your cold start issues.

David

and dave, i do hear and feel a miss when first starting it up and driving around for the first few minutes

thunderkid84
05-01-2009, 07:07 AM
Also, how old are the O2 sensors? Have they seen coolant? When was your fuel filter last changed? MAF wire last cleaned?

O2's, i believe, are less than 2 years old. they've never seen coolant, hg's have never blown.

fuel filter was changed about 7k ago.

maf wire was cleaned a few weeks ago.

thunderkid84
05-01-2009, 09:11 PM
bump

i need some help with this guys. gotta get it fixed in the next 2 weeks. pulling everything off to the fual rail tomorrow.

could it possibly be some bad o-rings ?

QuickMustang
05-01-2009, 11:27 PM
bump

i need some help with this guys. gotta get it fixed in the next 2 weeks. pulling everything off to the fual rail tomorrow.

could it possibly be some bad o-rings ?

If you smell or see gas around the injectors, then yes...If not, probably not...I'm still betting on the fuel pump...

birds4us
05-02-2009, 07:41 AM
My educated guess would be that since you replaced the fuel injectors, you may have cut an injector o-ring, or not have them seated properly into the fuel rail. Did you lubricate the o-rings when installing them into the rail and the intake? If you have a small vacuum leak it could cause the symptoms for the cold start, which could seal up when the engine gets hot. As for the fuel leak, it would cause the smell and the lack of pressure. Also it could be the check valve in the fuel pump for the instant drop off in pressure. You may have one problem or several. I would start at the fuel rail.

thunderkid84
05-02-2009, 11:15 AM
My educated guess would be that since you replaced the fuel injectors, you may have cut an injector o-ring, or not have them seated properly into the fuel rail. Did you lubricate the o-rings when installing them into the rail and the intake? If you have a small vacuum leak it could cause the symptoms for the cold start, which could seal up when the engine gets hot. As for the fuel leak, it would cause the smell and the lack of pressure. Also it could be the check valve in the fuel pump for the instant drop off in pressure. You may have one problem or several. I would start at the fuel rail.

will do

this sucks :(

thunderkid84
05-02-2009, 01:49 PM
pulling the fuel rail out now.

i noticed theres alot more oil in the system than normal. would a bad pcv valve do this ?

birds4us
05-02-2009, 02:02 PM
Oil in what system?

thunderkid84
05-02-2009, 04:14 PM
Oil in what system?


IC tubes, supercharger, return plenum

QuickMustang
05-02-2009, 04:48 PM
IC tubes, supercharger, return plenum

It's common to have some oil in there, but if it is excessive, then yes, it could be a PCV problem...However, I doubt it's related to your cold start issue...

thunderkid84
05-02-2009, 04:53 PM
It's common to have some oil in there, but if it is excessive, then yes, it could be a PCV problem...However, I doubt it's related to your cold start issue...

oh i know that....im no newbie

bought all new injector o rings and new ring on the regulator. one injector ring was split and the regulator ring was splitting in half.

tried to put the rail back in but it started raining......:(

thunderkid84
05-02-2009, 07:47 PM
everything is back together.

rtv is drying and the battery is disconnected.

we'll see what happens.........

thunderkid84
05-02-2009, 09:33 PM
At first the car didnt want to start. I read an old thread and then tried unplugging the TPS and ....bam ! fired right up

idle was ok. got a CEL.

decided to park it and plug the TPS back in. CEL went away but idle was stupid high, 1700 something.

drove around for a bit. cut the car off and tried to start again....nothing. unplugged the TPS and.....u guessed it ......fired up.

it runs sooooo much better with it uplugged.

so is my TPS bad now or just need adjusting.....AGAIN :rolleyes:

thunderkid84
05-04-2009, 08:20 AM
well, i guess i had to "re-dial-in" the tps. put it to .93v and wot is 4.75.

been running pretty good. cold start-up this morning was ok. took a few secs of cranking, then fired up to 1500 and slowly came down. didnt notice a miss either.

so...hopefully she's fixed

thunderkid84
05-05-2009, 01:20 PM
alright, so i've done several cold starts and it does take a second or 2 to fire up, then it runs rough for 1 or 2 seconds then kicks the rpm's up and runs fine from there on.

does it still sound like a check valve problem ?

or more like bad fuel filter or cam sensor/DIS ?

Scott Long
05-05-2009, 07:02 PM
Hard to say... If you want piece of mind, do like I did and change all of them.

thunderkid84
05-05-2009, 07:21 PM
right :rolleyes:, u know how much money that would cost ?:eek:

David Neibert
05-06-2009, 11:12 AM
alright, so i've done several cold starts and it does take a second or 2 to fire up, then it runs rough for 1 or 2 seconds then kicks the rpm's up and runs fine from there on.

does it still sound like a check valve problem ?

or more like bad fuel filter or cam sensor/DIS ?

Doesn't sound like anything unusual for a modded SC...I'd stop messing with it.

David

thunderkid84
05-06-2009, 01:20 PM
Doesn't sound like anything unusual for a modded SC...I'd stop messing with it.

David

ok. so it just has something to do with all the mods and the chip and stuff ?

David Neibert
05-06-2009, 02:26 PM
ok. so it just has something to do with all the mods and the chip and stuff ?

Maybe... Just saying it doesn't sound like there is really anything to be concerned about if the only problems are being a little hard to start and rough idle for a few seconds.

David

thunderkid84
05-06-2009, 04:48 PM
ok thanks dave

Scott Long
05-06-2009, 08:16 PM
right :rolleyes:, u know how much money that would cost ?:eek:

I think I spent around $400 on parts to replace them on my car after I got out of tech school.

thunderkid84
05-06-2009, 10:16 PM
yea but that $400 could go towards an MP plenum ;)

thunderkid84
05-11-2009, 07:53 PM
scott, did u ever fix your sc that had the fuel pump or ircm problem ?