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1993 Chevy S-10 1993 S-10 Blazer not starting unless it is p

Tiny
NOVACLONE
  • MEMBER
  • 1993 CHEVROLET S-10
1993 Chevy S-10 6 cyl Four Wheel Drive Automatic? Miles

I bought a 1993 s10 Blazer 4.3 cpi, that was not starting by itself. The fuel pressure shows 55psi when you turn key to on and does stay there. When you crank it over, the fuel pressure drops to a few pounds and the engine does not start. It has had a new distributor with a new module installed, fuel filter changed, and all of the fuses checked and are good.I found that the engine will start right up if it is primed manually. Also what I found is that after running the battery down and attaching a battery charger, the fuel pressure shows to be at 60 psi with the key turned to the on position and will start right up with no priming involved. The previous guy who owned this told me that the only way it started with him was to jump start it. After it is started and the battery charger removed, the engine will start again right away. With the battery charged, the engine will start every time for about up to 30 minutes after the battery charger was installed with 60 psi still showing on the gauge with key to the on position.I can wait about 2 hours later and try to start, and I'm back to no start without a prime, or by simply hooking up the battery charger and seeing that the fuel pressure was at 60 psi. I, m lost.
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Monday, April 14th, 2008 AT 10:46 AM

10 Replies

Tiny
DENNYP
  • MECHANIC
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First, test the battery and make sure the cable ends are clean. Next, when it acts up, check the spark at a plug wire. It should be a bright blue spark. Let me know what you find.
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Monday, April 14th, 2008 AT 4:33 PM
Tiny
SERVICE WRITER
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I not sure why a battery charger would cause a priming condition. Setting that aside, it almost sounds like the fuel is draining back. If your were to cycle the key several times, does it start right up?
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Monday, April 14th, 2008 AT 5:25 PM
Tiny
SERVICE WRITER
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I got the PM on the cycling making no differenence.

Here is what I do know and is consistent with your symptoms. The pressure has to be 60psi or higher to start the truck, but it can run on 55 psi. This points to a faulty pump.

What doesn't make sense to me is the bit about charging the battery gives it a boost to 60 psi. I ran accross something that related to this, if I can find it, I'll update it.

I know the psi specs are critical on these for starting.
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Monday, April 14th, 2008 AT 7:23 PM
Tiny
MASTERTECHTIM
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This is definitely caused by a bad fuel pump and pulsator. The pulsator is what connects pump to the sending unit. To know for sure you need to do a amp draw test on the fuel pump lead and it should be atleast 9 amps. What you have is a weak pump or the pulsator and you are compensating for it by adding more voltage to pump. I hqave seen your exact problem a hundred times and this is the fix. Let me know. ****Also make sure the connector to the pump is not melted at all.
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Tuesday, April 15th, 2008 AT 1:14 PM
Tiny
NOVACLONE
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Tuesday, April 15th, 2008 AT 2:20 PM
Tiny
2CARPRO JACK
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Most pumps come with a piece of fuel injection hose to do away with the pulse dampener Tim speaks of, which sounds right on the money
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Friday, April 18th, 2008 AT 7:42 AM
Tiny
NOVACLONE
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Thank you, I'm currently installing fuel pump and I will let you know the outcome. Gary Brooks.
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Friday, April 18th, 2008 AT 11:44 AM
Tiny
SERVICE WRITER
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I thought it pointed to the pump pretty well, but what I still don't understand is the bit about charging the battery gives it a boost to 60 psi.
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Friday, April 18th, 2008 AT 5:47 PM
Tiny
DENNYP
  • MECHANIC
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No kidding, If you have to have a fully charged battery and a jump box to get 60psi on the pump, then that pump should be pulling enough amps to blow the fuse. Sounds like there is somethimg missing from the picture.
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Sunday, April 20th, 2008 AT 7:05 AM
Tiny
FWUPOW
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I had this same problem with my '96 Chevy Blazer when I first bought it used and I found that the battery was bad and apparantly also the fuel pump motor has been on it's last legs.

I'm replacing the fuel pump right now. My fuel pressure was only 49-50 psi KOEO (curious how the letter "O" stands for both "ON" and "OFF" isn't it?)

The translucent ribbed hose in the fuel pump module, which I'm assuming is the pulse dampener appears to be fine on my old pump. Also my electrical connections to the pump and within the pump show no corrosions or heat induced melting. I'm guessing and hoping that my pump motor has worn contacts which are causing reduced rpm and pressure.

"Scope Tests
By connecting a Low Amps probe to the fuel pump's voltage supply wire, you can create a scope waveform that will reveal internal wear in the brushes and commutator that may not show up in a traditional pressure or volume test.

Observing the waveform will tell you if the pump's amp draw is normal for the application or is high or low, and if the pump is operating at normal speed or is running slow. Problems such as a bad spot on a commutator or a short or open in the armature also will be obvious in the waveform.

A "good" electric fuel pump waveform will generally seesaw back and forth with relative consistency and minimal variation between the highs and lows. A "bad" waveform will show large or irregular drops in the pattern, with large differences between the highs and lows.--By Larry Carley, Copyright 2005"
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Wednesday, August 20th, 2008 AT 11:09 AM

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