[Supras] Warm Start Stumble

[Don Ewing]

I agree with this.  When the weather around here gets warm and we are still on oxygenated fuel I have the same problem.  I have come to the realization that this is vapor lock because the fuel just evaporates at a lower tempreture.
  Don

berniek at technicaldevelop.com wrote:
  Skip, et al:

As stated before, my essentially stock '90T did this. When I built the
'91 I used ND 550cc injectors, and had a fuel pressure gauge on the rail. 
Although the gauge has since been replaced with a Schrader valve (gauge
would wear out from lack of damping), it showed that pressure held for
hours after shutdown. So at least in my case, the problem strongly
appears to be a latter day form of vapor lock. Happens only on warm-hot
days especially when using gas that was formulated for cooler weather.

BernieK

> Bernie, Supraman, & Group,
>
> Hope this helps; I chased something like this until someone told
> me what's below.
> If your car stumbles on hot start up (after its been sitting for
> at about ten minutes) and it also stumbles on cold start, but, in both
> cases idles fine after less than a minute (without revving it up), you
> need to check for injector(s) that are leaking (very slow leak) when the
> engine is off. With this type of leakage, when you turn off the car,
> fuel leaks very slowly into one or more cylinders causing, on start-up,
> a very rich mixture until the excess fuel burns off. Easiest way to
> check for this is, after using the car, let it sit overnight and, before
> starting, check for fuel pressure in the rail in the morning. It should
> hold most (if not all) of the pressure overnight. If the pressure's all
> bled off, before starting the car, pull the plugs and smell for fuel.
> Any easier test is to pull the hose that's connected to the throttle
> body, open the throttle plate and smell inside the intake - it should
> not smell strongly of gas after its sat overnight.
>
> Good Luck, Skip
> '86 MA70 Supra (still alive & kicking !!!)
>
> -----------------------------------------------------------
> Date: Wed, 23 Apr 2008 14:58:56 -0400
> From: supraman88 
> Subject: Re: [Supras] Warm start stumble
> To: berniek at technicaldevelop.com
> Cc: "Supras at supras.com" 
> Message-ID: <480F86F0.5020703 at verizon.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> berniek at technicaldevelop.com wrote:
>> I had that problem for years with my former '90 and now have it with
>> my modified '91 now that the weather here in NJ has become warm. It
>> appears to be fuel vaporization in the rail and lines during "hot
>> soak", nothing to worry about. Just hold the throttle above idle for
>> about 20 seconds and you should be fine. If the problem persists
>> beyond about 20 seconds, it is probably another problem, but I think
>> you will find the hot soak vaporization to be the culprit.
>
> Thanks, that is exactly what I have been doing! It appears to be running
> rich when this happens.
>
> It never did it before I replaced the tanks and eliminated the leaks in
> the filler neck.
> I'm wondering if there is a difference between US and Canadian models
> prior to 1991.
> It had a different gas cap before. Maybe I'll swap those and see what
> happens.
>
>>
>> The cold start injector has a bimetal contact timer in the thermostat
>> housing to actuate the cold start injector only when cold. You can
>> disconnect it as a test, but again I don't think that is the problem.
>>
>> Hope this helps.
>>
>>
>> BernieK
>> '91T 5 speed, refreshed JDM, '98 MkIV wheels, Lexus AFM, 550cc ND
>> injectors, Walbro, modified stock adjustable FPR, 57 trim CT26 (no
>> turbine clip, but wastegate passage bored out), deflashed valve bowls,
>> '98 mounts (strong!), Treadstone IC, hard piping, Lipp, 3" Random Tech
>
>> downpipe and single cat, 80 mm HKS LET-T16 exhaust, Dawes ball and
>> spring boost controller (for now, set to 17 PSI), modified Raptor
>> recirculated BOV, 2 mm Cometic HG, ARP head studs, helicoiled exhaust
>> stud tappings, chrome moly lightweight flywheel, Exedy organic clutch
>> (street use).
>



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