Weird engine problem, 4 true mechanic only

SIDMAN · 09-09-2006, 12:34 PM

I want to hear from a mechanic that thinks they know what is wrong with my blazer.
It will not start on first start of day without using starting fluid..unless you hook a battery booster to it. the remainder starts of the day will work like a charm.
So to start it you can either hook a booster to it, or use starting fluid in it.

I have good fuel pressure 52lbs
This is the second fuel pump
Have changed 2 battteries with new. so good volts.
I have good spark. Starts as soon as you hook up boosters or spray starting fluid.
It sound like the injectors aren't getting enough voltage until you hook up boosters, for the initial start of the day. Then after the initail start you can turn it off for hours and it will restart without boosters or starting fluid.

I was thinking maybe a short pulling down my volts to injectors or computer not getting enough volts.

anyhow if you think you can help please reply. I want to shoot it and put me out of my misery.

Thanks
Sidman

muddog321 · 09-09-2006, 01:29 PM

Year? Book is 58-64 psi KOEO to start 96up injected motors. Heres an article on injection and 96up is in it calling for a min of 60 to start. 52 is OK running pressure.
http://www.babcox.com/editorial/us/us30098.htm
Hope that helps you, would explain the cold start failure and don't forget the pressure regulator under the upper intake on the injector assembly.

BlazerLT · 09-09-2006, 01:42 PM

What year do you have?

SIDMAN · 09-10-2006, 04:14 PM

First, I appreciate your replies. It is a 96.

Here is what is does
When i turn the key on 52psi. Try to start 52psi (No start)
When i put jumpers on it, it jumps to 58-60 psi and starts.
The battery is new, The fuel pump is the second one. I have tried other batteries from my other cars also. I am thinking about pulling the connector at fuel pump and checking volts with no booster and volts with booster to see the difference in volts. just hate to have to climb under. Hopefully wont have to drop tank.

Thanks for replying to my post and thanks for the link.

Sidman

BlazerLT · 09-10-2006, 04:54 PM

Quote:

Originally Posted by SIDMAN

First, I appreciate your replies. It is a 96.

Here is what is does
When i turn the key on 52psi. Try to start 52psi (No start)
When i put jumpers on it, it jumps to 58-60 psi and starts.
The battery is new, The fuel pump is the second one. I have tried other batteries from my other cars also. I am thinking about pulling the connector at fuel pump and checking volts with no booster and volts with booster to see the difference in volts. just hate to have to climb under. Hopefully wont have to drop tank.

Thanks for replying to my post and thanks for the link.

Sidman

52psi is really LOW for a 1996.

1996 should have 61-66psi minimum for the system work.

This will be caused by:

1.) Failing fuel pump
2.) Bad fuel pressure regulator.
3.) Plugged fuel filter.
4.) Battery voltage not good enough. Should be above 12.8volts fully charged.

Too bad you did all thos repairs without doing your rearch first, we could have saved you some serious money.

SIDMAN · 09-10-2006, 09:20 PM

Blazer,

The weird thing is how the booster allows the fuel pump to get me to the pressure i need. Something isn't getting enough voltage for some reason. Once i check voltage at pump I should be able to trace down the reason.Without schematics, I would think that the igniton sends power to the pump and then something cuts volts to the pump once it gets x amount of pressure.

SIDMAN · 09-10-2006, 09:20 PM

Blazer,

The weird thing is how the booster allows the fuel pump to get me to the pressure i need. Something isn't getting enough voltage for some reason. Once i check voltage at pump I should be able to trace down the reason.Without schematics, I would think that the igniton sends power to the pump and then something cuts volts to the pump once it gets x amount of pressure.

BlazerLT · 09-10-2006, 09:46 PM

Booster's usually run at a little higher voltage than your standard battery.

They usually are at about 14-15 volts which could be compensating for the weak pump at that time.

corning_d3 · 09-10-2006, 10:34 PM

Or he could have a bad fuel pump connector. Don't you get a new connector with every pump because they fail often?

You've most def. got high resistance somewhere if your pump and regulator are up to par...

SIDMAN · 09-10-2006, 11:53 PM

Alright,

I disconnected my fuel pump connector and set my multimeter to read the volts when i turned key on. On key on engine off it read 12.2 volts for about 1sec and then dropped to 3.5 volts. When i hooked booster up it read 12.7 volts for 1 sec and then dropped to 4.2 volts. What tells my volts to kick on 12 volts for a second and then cut voltage to 3-4 volts? Is it set up to prime fuel line before you turn key to start position? Also there are 2 connectors on my fuel pump. 1 has 3 prongs running in line, which when disconnected still allows fuel pump to run. the other connector is 4 prong which according to my Haynes manual is sending unit and fuel pump signal and ground. What is the 3 prong? Another thing, my Haynes manual says the 4 prong is 97 and up but my blazer is 96.

Thanks for replying.

I am determined to fix this, for knowledge if nothing else. Tomorrow i will change fuel filter probably just to eliminate it. It could be the pump pumping more with more volts but it is doing the exact same as the old pump, and I find that odd.

Blue Bowtie · 09-11-2006, 10:06 AM

The relay should provide full battery voltage to the pump for a two-second prime cycle when the ignition is first turned on. The relay is operated by the PCM. When the relay shuts off, pump pressure should drop to zero, not 3-4 volts. If you are still measuring voltage at the pump leads when the relay is off, either the relay is coated with carbon and flashover damage, or the oil pressure switch is partially conductive. If the relay is damaged, that may be a major part of the problem with low voltage during cranking.

Low pump voltage during prime will certainly lower the output pressure. Electric pumps are extremely sensitive to input voltage. Check for voltage drop at the relay itself, and at all the connectors between the relay and pump. You also need to check any grounds for the pump, one of which should be near the tank. Any resistance in any part of the circuit should be revealed with a voltage drop test. You will likely have to jumper the relay to maintain power in the circuit for diagnosis.

There are several connectors right at the tank unit itself, and one near the tank. Unfortunately, at least two of the connectors are inside the tank.

It seems that the pump itself may be intact, but cannot produce the necessary 61 PSIG on startup due to low voltage. I've experienced this myself several times.

BlazerLT · 09-11-2006, 11:16 AM

The fuel pressure should NOT drop to zero after the prime cycle, it is supposed to hold it at that pressure to start the vehicle.

12.2 volts is low for a battery. Minimum it should be is 12.6v.

MT-2500 · 09-11-2006, 11:25 AM

Quote:

Originally Posted by SIDMAN

I want to hear from a mechanic that thinks they know what is wrong with my blazer.
It will not start on first start of day without using starting fluid..unless you hook a battery booster to it. the remainder starts of the day will work like a charm.
So to start it you can either hook a booster to it, or use starting fluid in it.

I have good fuel pressure 52lbs
This is the second fuel pump
Have changed 2 battteries with new. so good volts.
I have good spark. Starts as soon as you hook up boosters or spray starting fluid.
It sound like the injectors aren't getting enough voltage until you hook up boosters, for the initial start of the day. Then after the initail start you can turn it off for hours and it will restart without boosters or starting fluid.

I was thinking maybe a short pulling down my volts to injectors or computer not getting enough volts.

anyhow if you think you can help please reply. I want to shoot it and put me out of my misery.

Thanks
Sidman

52 lbs of fuel pressure will not get the job done.
You need over 62 lbs of pressure to squirt the injectors on a cold start.
You need good voltage to fuel pump but also a good ground.
Check both.
If you get both then check pump pressure.
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

corning_d3 · 09-11-2006, 02:10 PM

Quote:

Originally Posted by SIDMAN

1 has 3 prongs running in line, which when disconnected still allows fuel pump to run.

That would be the vacuum sensor for the tank. Kinda like a MAP sensor.

redwheeler · 09-11-2006, 07:58 PM

ok blue bowtie hit this one right on the head it is not getting enough power and a voltage drop test needs to be proformed before any thing elese is done post any results also if you wanna check for dead resistance get youre self a good multimeter and check the ohms of resistance in the curcut go from batt to relay then from relay to pump pump to ground please post any results

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