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mr 4 speed

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1970 SS454 LS6 11 second street car
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Discussion starter · #1 ·
What would cause a hard start when cold? Engine takes quite a few cranks (ALOT) to start when cold,but starts fine when warm..its a 4.3 Vortech...any ideas? TIA
After thought..do these have a cold start injector?
(sorry I posted this here..figured it might get more notice here)
 
#2 ·
I assume you checked for spark and injector pulse. I had one in my shop last year and finally traced is to a weak fuel pump. this fuel injection setup is very sensative to fuel pressure, a few pounds off and it wont start.
Also check the fuel filter, these are often overlooked. The engine coolant temperature sensor could be faulty as well as the inlet temp sensor there by telling the computer to give too much or not enough fuel. Hope this helps. dont hesitate to ask more questions.
 
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#3 ·
sorry read you post again it has spark.
also these engines dont have a cold start injector, they have a centrally located injector pod inside the intake manifold.
 
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#4 ·
My wife had a '94 GMC Jimmy that had the sme problem you are having. Took it to the dealer(still under warrenty,sp?) they said it was the injectors. They replaced all 6 of them and showed me the old ones. It stared the first time everytime after that. Hope this helps.
 
#6 ·
first thing to check would be your coolant temp . sensor , this sensor tells the computor the temp of the engine . so it can deliver the needed amount of fuel for a cold or warm engine.
 
Discussion starter · #7 ·
Guys,thanks for all the info.
This is what I do know:
It has a new GM fuel pump,less than a year old.
Has 40 psi/fuel pressure
Also,the injector rails (I think thats what they are) :confused: where replaced
The truck always ran mint,but this cold start issue started recently.It has slight hesitation too,but not not all the time.Sometimes it will run flawless.I was going to try the fuel filter 1st,then check out the coolant temp. sensor..how do I test that? Ohm meter?
 
#8 ·
Is it a CPI engine? Sometimes the injector o-ring leaks and floods the engine on cold start up.

The engines are also known for EGR valve problems. Maybe take it off and beat on it a little to knock the gunk out of it.
 
#9 ·
These also have an oil pressure switch. Yeah, I know, something else to chase down. :rolleyes: While I haven't done mine yet, the EGR can be restricted by using a penny with a small hole drilled into it.

Hell Chris, do what I did this weekend, pour an old can of Top Engine Cleaner down the throat of the tbi, WOW, what a smoke show!
 
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#10 ·
I had the same problem with a '92. If I remember correctly, there was a limited window for what the fuel pressure should be, and it was from 50-55PSI, not 40 psi. I had them go out every 2 years until one of the dealer's mechanics told me to never let the fuel go below 1/4 tank, then I stopped having trouble with the pumps.

Hate to say it, but I think your 1yr old fuel pump is the culprit.
 
#11 ·
You'd be surprised what a malfunctioning ECT (engine coolant temp. sensor) will do. One side effect is hard start. If you know anyone with a snap-on scan tool, or vantage - its quick and easy to test. Or, take the ECT out and place it in a pot of water, measure the resistance, as the water heats up, the resistance should not change. If it does, replace the sensor. Also, the voltage output of the sensor will change with a rise and fall in temp, you can back-probe the sensor to see what you get. Sorry, I dont have any resistance values for your ECT or voltage per temp charts in front of me, but in general, the voltage should decrease with higher temps, probably around 4.5-5v cold, and down to around 1v hot.

BTW, some more possible problems associated with a bad ECT sensor are:
-Rich or Lean A/F ratio
-Improper operation of emissions devices
-Reduced fuel economy
-Improper converter clutch lockup
-Hesitation on acceleration
-Stalling
 
Discussion starter · #12 ·
Guys,this is all good
Image

I have the fuel filter all ready..for what its worth,I'll change that tonight,and see what happens..and thats about all the time I will have.Tomorrow or Thursday I'll check out the coolant sensor.Thanks again
Image
 
#13 ·
Originally posted by mr 4 speed:
Guys,thanks for all the info.
This is what I do know:
It has a new GM fuel pump,less than a year old.
Has 40 psi/fuel pressure
Click to expand...
Originally posted by Xtreme70SS396:
I had the same problem with a '92. If I remember correctly, there was a limited window for what the fuel pressure should be, and it was from 50-55PSI, not 40 psi.
Click to expand...
If it's CPI and I think it is 40PSI won't cut it.
I think you indeed have a fuel problem. I'll go against the grain and say your wasting you time checking your ECT if it on cold startup. The computer has a preprogrammed fuel strategy until closed loop is achieved.
When you turn on the key the fuel pump should run for 2 seconds or so and you should see darn close to 55psi. If it reaches 55 and holds pretty close then your okay with the pump. It if reaches 55 then drops down signifcantly then either your fuel pump is bleeding down(possibly the pulsator which is the flexible line between the pump and metal line in the tank or your injectors are bleeding down. You could pinch off the flexible lines to determine where the bleed down exist. If you cannot achieve 55psi then either the pump is going out or possibly the fuel filter is restricting flow. Regardless you need at least 55psi to start central port injection. Don't matter if the fuel pump 1 year old or not. I wen't to work at a GM dealer in January. I kid you not there hasn't been I day that I can remember that somebody in the shop wasn't pulling a fuel tank. I've put more pumps in the last 6 months that I did the prior 15 years on the ricers.
FWIW at normal operating temperature you should
read around 1.5-2.0 volts if you backprobe the signal wire on the ECT. I think its a yellow wire.
If you ohm it you see somewhere about 7500 ohms at
70F down to 200 ohms or so at about 200F. Hope this helps...
 
#14 ·
Does the CPI 4.3 Vortec have two wires on the temp sending unit?

My 94 truck has the TBI 4.3 Vortec. Recently changed the temp sending unit in hopes of getting the temp gauge to work. This engine only has one dark green wire to the temp sender, but the same temp sender will also work with 2-wire applications.

Never had a cold start problem.

Jack, what's the deal with all these fuel pumps? Has GM made a better one, or do they just go bad often?
 
Discussion starter · #15 ·
update..
I changed the fuel filter last night..it sure looked like the original.Lots of debris/dirt/black gas would come out of it if you tapped on it.
Anyway,I turned the key on to prime the pump,and then it started right up.Ran mint too,pulled to the 5K shift point no problem.I'll have to recheck the fuel pressure next.
 
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mr 4 speed
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