Cold start miss/stumble

[Typhoon]

Hi all,
I have an 88 Supra with 7MGTE. The car is new to me, Ihave done aproximately 500kms with it.
It is completely stock and just had a new head gasket put in by me(yes I know what I am doing, the head gasket is all sorted).
Anyway, when the car has it's first start for the day, it cranks over and catches on a few cylinders, stumbles roughly and runs slowly, then settles into it's regular 1200-1300 rpm cold idle smooth as glass. This whole process takes maybe five seconds. There is no backfire through inlet or any exhaust popping.
Sometimes when it does this, it makes that air under pressure or vacuum squeal very briefly, it may or may not be the problem, or may be some part of the emission control/cold idle/ISC system having a fit due to the weird start.
I am guessing the areas of concern would be fuel pressure dropping off overnight (leading to no fuel), no cold start injector(lean mix), small air leak(lean mix), or incorrectly routed vacuum line somwhere? Any suggestions appreciated, the car runs faultlessly during every other phase of operation and I have no ECU codes.

Regards, Andrew.

 

[tlo86]

sounds like a vac leak. if you can start it then it seems like it is small. any hissing from the engine? dies when you rev high?

same symtoms i had with a vac leak at least

 

[Typhoon]

Yeah, could be a vacuum leak. Engine got new intake gaskets, but with the amount of vacuum hoses on these engines(I think Toyota got a job lot somehwere and had to use it all up!) it could be a hose has cracked when I pulled it all apart.
Only does it on cold start though, is there some cold start device that needs vacuum?

Yegards, Andrew.

 

[plaaya69]

Good description Andrew, I would say also see of you can hear a hissing coming from the motor(near the intake side) and recheck all of the clamps on the intercooler piping especially the 2 clamps on the hose that comes off ot the 3000 intake pipe and goes to the TB.

 

[jetjock]

Hello Andrew. It does sound like a starting enrichment issue caused by either a faulty cold start injection, pirate air, or both. Since the cold idle is correct the coolant sensor is working. Check the cold start injection components including the thermo-time switch. Keep in mind the CSI system is hard wired so as to operate only during cranking.

Listen for the idle speed valve to click full open just after the engine is shut off. Since cold idle speed is good I doubt it's the problem though. Any difference in starting when you hold the pedal 1/4 way down? Also verify timing is set to 10 btdc since base timing is what the ecu uses when starting the engine and whenever rpm is below 500.

If your car has an EGR valve make sure it's not leaking. If you have a EVAP system disconnect and block the port on the throttle body and see if there's an improvement.

Overnight loss of fuel system rest pressure is normal and causes problematic hot, not cold, starts. That said the fuel pump on your car doesn't run until the engine is cranked. Try priming the fuel system before the first start of the day by jumpering B and FP in the diagnostic block for 5 seconds with the key on. Remove jumper and see if the car starts better. I'm betting on the cold start system or pirate air though.

And plaaya is right: That was a good post. It'd be nice if everyone could do as well. Sure beats the "Help! Car broke!" ones.

 

[Typhoon]

Thanks for the information guys. I try to add as much information as I can when asking for help, you know the saying "garbage in, garbage out"!
I'm off to the garage now to try out those troubleshooting tips.
*EDIT* O.K, forcing the cold start injector with ign on and bridging B and FP didn't help, I could hear CSI spraying away (probably hurt a little, slightly longer craking time to start, not sure). Ignitin timing is at 10btdc (when terminals bridged as per manual). Idle speed valve clicks a few times after engine shut down.
Next stop is EGR and vacuum leaks.
Thanks again, really narrowing it down now!

Regards, Andrew.

 

[flubyux2]

who told you to jump the B+ and FP together to get the CSI to inject fuel???

the B+ and FP just energizes the fuel pump.

 

[Typhoon]

Yeah, it does, and with the ignition on, you can hear the CSI squirting, or the fuel running through the fuel rail, one of the two!
Either way, it ruled out fuel pressure as a problem.

Regards, andrew.

 

[jetjock]

who told you to jump the B+ and FP together to get the CSI to inject fuel??? the B+ and FP just energizes the fuel pump.

Well no shit Sherlock. I told him to do it but not to get the CSI to run, only to build fuel pressure. Read the post. He needs to do the same thing. What part of "the CSI system is hard wired so as to operate only during cranking" didn't you understand Andrew?

 

[Typhoon]

Well no shit Sherlock. I told him to do it but not to get the CSI to run, only to build fuel pressure. Read the post. He needs to do the same thing. What part of "the CSI system is hard wired so as to operate only during cranking" didn't you understand Andrew?

Yes I understand that now. I misread it initially.
Anyway, as I said above, the fuel pump building pressure before start didn't do anything so I am back to looking for vacuum/ EGR leaks.

Regards, Andrew.

 

[PROJECT N00b]

Maybe your cold start plug is unplugged...right where the intake manifold splits into 2 pipes...mine was unplugged, and eversince i plugged it back it, its been fine.

 

[jetjock]

The CSI is the next thing he should test. Andrew: All testing the fuel pressure did was eliminate one item. With the engine cold take the CSI out and stick in a bottle. See if it sprays while cranking. It's likely all gunked up so clean it.

 

[Typhoon]

THAT sounds plausible and an extremely good idea. Off to do it now.

Regards, Andrew.

 

[Typhoon]

CSI looked like a stick of licorice, cleaned thoroughly with lacquer thinners, works mucho better!
I owe you guys a beer if you're ever in Australia!

Regards, Andrew.

 

[PROJECT N00b]

So, it worked?

 

[tlo86]

The CSI is the next thing he should test. Andrew: All testing the fuel pressure did was eliminate one item. With the engine cold take the CSI out and stick in a bottle. See if it sprays while cranking. It's likely all gunked up so clean it.

:2ar15:

 

[jetjock]

^ Not sure what that's supposed to mean.

That it worked makes sense considering his symptom and it being winter where he lives. Andrew: The CSI needs to be kept clean. Opening the throttle and using a torch to inspect/shoot it with spray solvent should be a procedure associated with whenever the induction pipe is off the engine. The same goes for the interior of the throttle body and it's ports.

 

[tlo86]

its good dont worry hehe, "badass answer" i guess

 

[flubyux2]

jetjock... i didnt see where anyone said that jumpering those 2 terminals also created the CSI to hang open. thats what threw me off when he said the CSI was operating when those terminals were jumped.

the CSI isnt exactly necessary. its just for really cold starts. you can live w/o it even during cold starts, it just takes an extra second of cranking before itll catch. i dont have mine in my ffi and it starts like stock. in fact, i have too much fuel when i cold start it, but thats probably cuz my injectors are dirty.

if i were you, id just order a new full silicone hose kit and replace EVERY single line on your car. consider it part of a PMCL so your car will run the way it should

 

[jetjock]

Damn, a bright guy like you should work for the automakers since you know so much more than their engineers. Toyota could've used your talents when they choose to spend all that money putting a entirely superfluous system on their engines. Just think, they could've saved it and sold their cars for less or the same, either making them more competitive in the marketplace or increasing their bottom line by millions. The fools.

Maybe the CSI system isn't needed is balmy St Pete but did it occur to you it might be in colder climates? Must be why this and pretty much every car built by all the automakers since the late 70s has one. His symptom wasn't hard starting btw...