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Mcostello
07-12-2011, 06:01 PM
I respect the opinions of the members here much more than a board that I know nothing about which is why I posted this here.

I have a 1994 S-10 that has an occasional hard start problem. Acts like it's flooding, replaced both injectors, and made the problem better for a month or two. Now it's back again, could an injector have gone bad already? Is there a better way to diagnose this problem than waiting for a drip to fall from the injector. Any hints or other solutions. Thanks for the help, Mark

JanvanSaane
07-12-2011, 06:12 PM
The first two things I would check, MAP sensor, fuel pressure regulator.

Your Old Dog
07-12-2011, 06:19 PM
Is somebody putting higher octane fuel in it then it was designed for? My old company car wanted 87 octane and it fired right up. Put the really high octane stuff in it thinking you were helping it and it was hard to start. Gooder is not always better :D

aboard_epsilon
07-12-2011, 06:20 PM
First thing i would look at is the coolant temperature sensor ..cheap to replace ..and its the cause of many problems ..it would be like trying to start a warm engine on full choke if it buggers up ..

is it idling high .if it is ..look at that sensor .

all the best.markj

saltmine
07-12-2011, 07:01 PM
Check the fuel pressure.

I can't even begin to tell you how many times I've had guys come in the shop (when I was working) complaining about hard starting , poor performance, misfires, hesitation, you name it. Many have replaced everything on the truck but the hubcaps, with no luck. S-10's are notorious for being sensitive to fuel pressure...usually lower than normal.
Hard starting is usually brought on by fuel draining back through improperly sealing check valves in the fuel pump. When you go to start it, the priming relay runs the pump for 7 seconds, then cuts off, waiting for the oil pressure switch to close, keeping the pump running as long as there's oil pressure.
Most of the time, 7 seconds isn't enough time to re-pressurize the fuel system, so, you end up cranking for a bit while the oil pressure comes up.
It's especially bad on TBI injected S-10's because the nominal fuel pressure is 13 psi. With TBI, the engine won't start and sometimes will only idle when pressure drops below 10 psi.

topct
07-12-2011, 07:56 PM
A bad fuel pressure regulator will cause this problem.

It does sound like a loss of static fuel pressure.

A.K. Boomer
07-12-2011, 08:48 PM
what is it S-10 week here or something? ;)

Willy
07-12-2011, 09:11 PM
Like saltmine said, fuel pressure, or the lack of it is an issue in hard starting complaints, especially in TB injected vehicles.
Try turning the key on and then off for 2-3 ten second cycles before actually starting the engine to see if bringing the system up to pressure this way has any effect.

Also, you say it exhibits symptoms of flooding when it is hard to start.
What type of indicators is the engine displaying to lead you to think it may be flooded?
In addition you make no mention of the particulars involved when it is hard to start. For example, is this first thing in the morning when cool and after it has sat idle all night? Or perhaps when hot and heat soaked after a half hour in a hot parking lot?
Try to find a pattern to when it seems most prone to hard starting...if you can, it may help us in assisting in diagnosing the problem.

Mcostello
07-12-2011, 09:43 PM
No problem starting when cold. It makes that rapid cranking sound when it happens. If I go into a store for a minute and try to start is when it shows up. Fuel pump replaced due to failure about 1 year ago. Everything I've done seems to fix it for about a month then it's back. Coolant temp gauge did just start to indicating lower than usual temperature, I'll replace that next.
It will eventually start if the gas petal is held to the floor. Guess I'll have to cut the gas line and mount a gauge to check for when it happens again.

Willy
07-12-2011, 11:02 PM
It almost sounds as if your S-10's ECM is getting an erroneous temp reference from the temp sending unit.
This would result in your ECM providing a richer mixture to what it thinks is a cold engine.

An OBD II scan tool is invaluable for verifying the readings it receives from the various sensors and confirming a diagnosis. Also fuel trim data will also confirm that the engine is being over-fueled. Although it's being told to essentially over-fuel a warm engine because it thinks it's cold.

The fuel trim is an adaptive technology that takes readings from the O2 sensors before and after the catalytic converter in order to keep the engine operating at a stoichiometric correct fuel/air ratio, in spite of minor variables like wear,minor vacuum leaks, variations in fuel pressure, misinformation from sensors, etc.etc..

Replace the temp sender and see if the hard starting when warm improves.
It's got to be done anyway, it's cheap and easy, and it will at least take this variable out of the equation.

saltmine
07-13-2011, 02:16 AM
Low coolant temperature might be something to look into.
A stuck open thermostat can make life miserable for just about any late model vehicle owner. Not only does it convince your ECM that the engine is cold, but it also cuts deeply into your fuel economy.

Back in the early '80's when the S-10's were fairly new, guys used to think they would get more power and make the engine live longer by installing a 160 degree thermostat. Wrong! Way wrong. Not only did the ECM think the engine was always cold, but the ECM also refused to apply the torque converter clutch (the only way to keep a 700R4 cool). You see, the ECM has to see at least 185 degrees of coolant temperature before it will allow the torque converter clutch to engage. We had quite a few S-10's with burned up transmissions get warranty repairs denied because the owner had installed a 160 degree thermostat.
The 2.8 V-6 had another way of telling it's owner it didn't like low temperature thermostats.....The oil would thicken, and the little engine would start spitting pushrods out. More than once, I've seen as many as four pushrods sticking out of a 2.8's valve covers...with a brand new 160 thermostat.

aboard_epsilon
07-13-2011, 05:48 AM
No problem starting when cold. It makes that rapid cranking sound when it happens. If I go into a store for a minute and try to start is when it shows up. Fuel pump replaced due to failure about 1 year ago. Everything I've done seems to fix it for about a month then it's back. Coolant temp gauge did just start to indicating lower than usual temperature, I'll replace that next.
It will eventually start if the gas petal is held to the floor. Guess I'll have to cut the gas line and mount a gauge to check for when it happens again.

The coolant temperature sensor for the gauge is just that ..

There is a separate sensor for the engine management

coolant sensor for the gauge ..usually has one wire going to it

coolant temp sensor for the engine management usually has two wires

they are usually in the same location within inches of each other

you want to look at or test the engine management one .

all the best.markj

Mcostello
07-13-2011, 09:44 PM
Got a thermostat today but everybody is out of gaskets or "O" rings. Will try again tomorrow as this is the only ride and I don't want it to throw a shoe until another car is home.

Mcostello
07-25-2011, 02:44 PM
I have installed a new thermostat and temp gauge reads normal now. Have not had this problem until today, and it happened twice. I was at a city park and it refused to start, second time today) talking with ranger, and after about 5 minutes of intermittent trying, he said " do you want to try priming it." Thought it would not hurt to try. He went and got a cup of gas, put couple of drops in TBI, and it started right up. Got it home and it refused to start again, got couple drops of gas in it and it started right up again.
What functions as an accelerator pump for these injectors, does the computer handle this or does something inject some gas to start with?

Mcostello
09-10-2011, 10:36 PM
Have replaced both temp gauge sensor and Temp switch for the Engine management system. Still is hard to start when hot, and a squirt of gas fixes it. I guess the next thing is to fab up a fuel line tee to check fuel pressure. Would I want it in incoming line or in bypass line?

topct
09-11-2011, 05:55 PM
Bumped.............

I'm curious as to the cause of the problem. I'm still going to guess a fuel pressure regulator problem. Also keep in mind that a bad oil pressure sensor can shut off the fuel pump. Or keep it from turning on.

I would check the pressure side of the system. Especially observing what happens when the engine is shut off. The pressure should not drop.

And always be careful when loosening fuel lines on injected engines.

Mcostello
09-11-2011, 08:59 PM
I am going to fab up an adapter for the pressure side of the regulator and see what happens then. I just did not expect a fuel pump to intermittently fail after a year. Been fortunate with this truck and now get to relearn the basics again. Have to get around the "mysterious" computer part of the problem when it could be the basics. Thanks, will report back when done.

Mcostello
09-21-2011, 09:27 PM
Found correct bolt thread and sealed the return line, no rubber tubing to crimp closed. With pump on the system would not hold pressure without sealing the return line. Replaced the pressure regulator and problem has gone away,
(until the next time.) :) Fuel pump pressure went from 10 psi. to 15 psi, so maybe that was the problem. Left the gauge on it for a week and kept checking it and system does not always hold pressure, but it starts like old times now.

vpt
09-22-2011, 08:58 AM
Fuel pump...

Every chevy within 100 miles of me has had its fuel pump replaced because of random no start issues.

Mcostello
09-22-2011, 08:18 PM
If it happens again that's the only thing left.:)