View Full Version : Fuel Metering Question (Hot/Cold Engine)

03-13-2010, 08:17 PM
OK, I need to throw this out there. I should know this, and I think I do, but I am not sure.

Early fuel injected Toyota engines had cold start injectors and cold start timer switches. I get how they work very well. My 90 Celica 4A-FE has it on (but not the 91 Celica 4A-FE).

In the early 90's, Toyota started eliminating cold start injector systems on their engines. So how do engines on, say a 93 5S-FE, start when cold (when more fuel is needed) and warm (when less fuel is needed)? Is it only based on the engine coolant temperature going to the ECM, and the ECM regulating the fuel injector on-time?

03-13-2010, 09:45 PM
5s still has the CSI.

I can not remember at the moment all the sensors that contribute a signal in that system.

03-13-2010, 10:19 PM
No, the 5S-FE does not have CSI. My shop manual says only the 3S-GTE of 1993 has it. And my 93 5S-FE definitely does not have a fuel line coming off the fuel rail and into the intake manifold cold start injector either, like my 90 4A-FE has. Neither does my 91 4A-FE.

Doesn't really matter though. I'm just wondering about the princple of operation of an engine that does not have CSI, how it delivers more fuel in a cold engine vs. a warm one.

03-13-2010, 10:38 PM

My 5s has a CSI. perhaps it is one of those things that was dependent upon region.
Many of my other past vehicles had it depending on whether the vehicle was sold in a "cold" climate or not.

As to fuel delivery my guess is that it simply uses the ecu temp sensor to determine the volume of fuel necessary.

03-13-2010, 11:59 PM
either of you guys have a good tip on removing the supply line from the fuel filter? She is a huge PITA.

I have the Charcoal canister out of the car

03-14-2010, 12:25 AM
I remember when i had an open circuit in my maf system a toyota tech was telling me how one works. I paid attention but for me to put it into words and remember all the small details is difficult. Although im somewhat sure that you are mostly correct in wondering if the ecm goes through coolant temp.

On my 2nd gen 3sgte the colder it is the more time it takes to kick over, i wonder if it just kinda in the ball parks it with pulsing more/less due to coolant temp.

03-14-2010, 01:00 AM
Shadowlife25, what year 5S do you have?

I would have thought a shop manual would say something about region if it was region specific. At least in 1993, it doesn't seem to be.

I'm sort of leaning the somewhere between the ambient air temp. sensor and the engine coolant sensor, the ECM probably handles cold starts by the normal fuel injectors then, on non-CSI engines. I don't know what else there is to introduce more fuel if there is no cold start injector.

Thanks, all!!!!!

Oh yeah, regarding the fuel filter supply line, I would like to know also. I only removed a fuel filter out of two Celicas, and it was a terrible job. And the maintenance manual doesn't even have a replacement interval on a fuel filter on a Celica. That doesn't make sense either, does it?

Shadowlife25, in looking through some Gen5 Celicas in AutoTrader.com, you are right, some 5S-FE's had them. Looks like 1990 & 1991 5S-FE engines had CSI. 1992 & 1993 did not. That's why my 1993 manual did not show any. So you must have a Celica 5S-FE that is 1991 or earlier, right?

03-14-2010, 11:44 PM
Actually later ;) But I replaced mine with one from a Camry due to the old motor dying.

For the filter, Toyota does not list a replacement interval since according to them, the filter is a "Lifetime" filter.
A set of line wrenches or crow's feet will do it just fine.

Be sure to soak top and bottom with penetrating oil for a couple days before you try to take it off.
It is apparently quite easy to bend the metal feed line.