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1996 Blazer S10 - Won't start


thomasrn
03-08-2005, 04:12 PM
I have a 1996 Blazer S10. It's on it's fourth fuel pump. They run for about 2 years then get swapped out. This is quite costly ( $800 ). Last one was swapped out 2 years ago.

I can crank and crank and crank the car, nothing happens. Battery is fine.

Checked for spark - God we got lots of spark! OUCH!! :iceslolan

During the hours of fighting trying to figure out what was wrong, we also hooked up a battery charger, and tried the 55 AMP engine start option to see if it was voltage related. Didn't help.

Hooked up a fuel pressure tester. Initialy (after sitting > 8 hours) I see around 15-20 PSI. When I turn the key on, the fuel pump runs about 2 seconds, I then see about 50-52 PSI.

The fuel pressure tester has a pressure purge valve, and small hose. I popped the PVC hose off the air intake, and ran the small hose such that the fuel would run into the intake manifold. Taking a pair of locking pliers, I locked the purge on the pressure guage on valve ON.

When you first turn the key on (but not cranking the engine), the fuel pump will run for about 2 seconds. This means that I just sprayed a small "metered" amount of fuel into the air intake on the intake manifold (If I were to crank the engine like this "BAD" things would happen! There is a point where you can put too much fuel into the intake manifold!). I then blow the last little bit of fuel trapped in the small hose into the manifold. Remove the locking pliers off the pressure guage, and replace the PVC hose.

Next I crank the engine, and it starts. It runs a little rough initially (10 secs), but all is well. I can drive the car around town, the highway, it's fine! Stopping the engine for less than 2 hours, it starts PERFECTLY. Wait longer than 2 hours, and I have to do the above steps to get it running again.

I do not see any check engine lights.

Obviously the engine is NOT getting fuel during the startup cycle!

My autotap scan tools tell me everything is "perfect", no pending, or active codes. I am however seeing in the history (A steady number that does not increase once the engine is running), a few misfires on Cylinder #6. Fuel pressure while driving ramps up to around 60 PSI.

At this time, I have a new Fuel Pressure regulator on order. Any thoughts on this?

Regards,
---- Robb -----

BlazerLT
03-08-2005, 04:57 PM
Take a voltmeter and measure what the battery voltage is with the engine turned off. Don't use the dash gauge, use an actual voltmeter.

Fuel pressure is to low.

You should have 60-66psi when having the key, but the engine not started.

You might need a new fuel pressure regulator, a new fuel filter, or maybe even a new fuel pump.

All three will not allow proper pressure to build.

ricksza
03-08-2005, 07:07 PM
Have you checked the fuel filter? This is a common cause for killing fuel pumps. When you check pressure, how quickly does it drop? As a band-aid, try: turn the key on for 5 seconds, turn the key off for 15, repeat twice and see if it starts. It would be better than pouring fuel into the intake.

thomasrn
03-08-2005, 08:21 PM
Have you checked the fuel filter? This is a common cause for killing fuel pumps. When you check pressure, how quickly does it drop? As a band-aid, try: turn the key on for 5 seconds, turn the key off for 15, repeat twice and see if it starts. It would be better than pouring fuel into the intake.

At Startup (Fuel Pump runs 2 secs):
=============================
Fuel Filter: Replaced 3 weeks ago. Done at every oil change.
Fuel Pressure: 50 PSI
- The pressure here does seem kinda low??
Battery Voltage:13.06 Volts (measured off the wires)

Tried the Key on/off approach, it almost caught, but didn't quite make it. But it was close!

Spayed fuel into the air intake: Engine started.

Engine Now at idle (running fine)
=========================
Fuel Pressure Now 54 PSI.

This is the MINIMUM pressure required to run the throttle body.

Engine now Driving
================
Fuel Pressure 52 to 62 PSI.

If I gun it to go up a steep hill, the pressure jumps to 62 PSI very quickly. It stays at 62 for only a moment. If I am running it hard, climbing up a hill, I see sustained readings of 58/59 PSI.

If coasting downhill: 52/53 PSI

If idling at a stop sign: 54 PSI

Fuel pump appears to be able to capable of delivering the fuel PSI needed to run the car. We are seeing 60-62 PSI spikes depending on driving conditions! So I don't ??think?? its the fuel pump (fingers crossed!).

So we come back to:
==================
Fuel Pressure Regulator?
Heard mention about another gizmo called a fuel pulser?

Thanks guys!

Regards,
---- Robb -----

BlazerLT
03-08-2005, 09:25 PM
You should have 60-66psi when the key is turned to the position before start as I said previously.

You need to replace the fuel pressure regulator.

blazee
03-08-2005, 09:44 PM
You should have 60-66psi when the key is turned to the position before start as I said previously.

You need to replace the fuel pressure regulator.



According to the GM shop manual with the key on and engine off:

the pressure should be 60 - 66 while the pump is running during the initial prime (or while kept running with a scan tool) after that it should be 55 - 60.

I'm not looking for an argument I just want to make sure people get the right info.

That being said...his pressure is still too low.

thomasrn
03-08-2005, 10:09 PM
According to the GM shop manual with the key on and engine off:

the pressure should be 60 - 66 while the pump is running during the initial prime (or while kept running with a scan tool) after that it should be 55 - 60.

I'm not looking for an argument I just want to make sure people get the right info.

That being said...his pressure is still too low.

Ahhh! I see! :grinyes:

Now that makes more sense to me! I was trying to understand where the 60-66 PSI came from. When I checked Alldata, it gave me a somewhat hard to understand description of all these pressure settings.

In alldata, it says in one spot that 55 PSI - 60 PSI as being fine, then in other parts it was talking about 60-66 PSI. I was trying to understand where this difference came from.

Thanks,
----- Robb -----

BlazerLT
03-09-2005, 01:29 AM
60-66psi is what you need when the fuel pump is priming, not 55psi.

55-60 should be the pressure when the engine is running.

ricksza
03-09-2005, 05:57 AM
Pressure reads too low, but that should cause some kind of performance problem at least a lean condition. Have you tried another fuel pressure gauge to verify your readings?
When the pump shuts off, does the pressure hold steady or does it drop? Your hard start sounds like a leak in the system also.

blazee
03-09-2005, 10:08 AM
60-66psi is what you need when the fuel pump is priming, not 55psi.

55-60 should be the pressure when the engine is running.
I didn't say it should be 55 while priming, I said it should be 55-60psi after priming with the key on and the engine off.

When you turn the key on, the pump runs for 2 seconds. While the pump is running the pressure should be 60-66psi (either during the 2 second prime or while keeping it running with a scan tool) This tells you that the pump is operating within spec.


When the pump primes and shuts off (engine still off) the pressure should hold between 55-60psi. This tells you that:

1) the fuel reached sufficient pressure to start the engine ( requires 54psi min. to open poppets)

2) there is not a significant loss of pressure, which would indicate one of the following:
-a) leaking fuel injectors
-b) damaged injector o-rings
-c) leaking pressure regulator
-d) damaged or split fuel pulsator
-e) leaking check valve
-f) leaking fuel lines


With the engine running the pressure should drop 3-10psi depending on engine speed due to vacuum on the regulator. This tell you that the regulator is operating properly, however it does not rule out the regulator leaking fuel.

thomasrn
03-09-2005, 12:19 PM
Pressure reads too low, but that should cause some kind of performance problem at least a lean condition.

Not exactly. Just like blazee says, I've read that we need a minimum of 54 PSI before the injectors on the car will even function. If you do not have this minimum pressure, you're kinda hosed! Hence I have been having to 'prime' the air intake manifold to get it started.

I am *NOT* getting the critical 54 PSI, and therefore I'm having one heck of a time getting the engine to start.

Have you tried another fuel pressure gauge to verify your readings?

Nope. But with seeing the pressure rise to the critical 54 PSI at idle, and seeing it jump around 58-60 PSI while running, I figure it's working 'reasonably well'.

When the pump shuts off, does the pressure hold steady or does it drop?

Holds reasonably steady, but does drop off over a few hours. Initially this drop in pressure was 'observable' and took about 5 mins. So things have been changing.

Your hard start sounds like a leak in the system also.

I'll keep that in mind. But I haven't seen and signs of leaking fuel.


Regards,
----- Robb -----

blazee
03-09-2005, 02:50 PM
What is your pressure during the 2 seconds the pump is running? If it is low even while the pump is running, but jumps to normal after started...it might be something as simple as dirty contacts inside the relay, as a back-up to the relay when the engine oil pressure reaches 4psi and over the oil pressure switch sends power to the pump on a wire that by-passes the relay. So...if the relay wasn't allowing enough power through to operate the pump at full capacity, you would have low pressure until the engine oil reached 4psi then the pump would have full power. The 4 psi would be reached by using starting fluid to fire the engine or can be achieved by an extended start time.


How fast does the pressure bleed off? You should not see much of a change and it should hold pretty steady for at least ten minutes. If it doesn't hold that would indicate a leak. You said earlier that you haven't seen any signs of a leak.....it could be leaking and you wouldn't even know it, if it were leaking inside the intake you wouldn't know without looking inside or a bad pulsator would leak back into the tank with no external signs at all.

BTW you should take any advice offered by ricksza he is one of the smartest guys on here.

thomasrn
03-10-2005, 02:14 PM
What is your pressure during the 2 seconds the pump is running? If it is low even while the pump is running, but jumps to normal after started...it might be something as simple as dirty contacts inside the relay, as a back-up to the relay when the engine oil pressure reaches 4psi and over the oil pressure switch sends power to the pump on a wire that by-passes the relay.

You know what, that 'does explain' what I'm seeing! I am not seeing the pressure go above 52 PSI even while the pump is running! And this is something that has been bugging me as to 'why'! :banghead:

Why is it when I crank the engine, I see diddley for fuel pressure? :banghead:

Why is it mechanics sometimes see too low a pressure, then for no
--reason it just 'goes away'? :banghead:

Why is it I've had to swap out 4 fuel pumps? 4*800 = $1,600.00 in fuel ---pump expenses. :banghead:

Fuel pumps don't just up and die at the rate of 1 every 2 years? :banghead:

What the hell is the 'problem' happening behind the scenes? :banghead:

You know, your relay theory 'would' in fact explains all this!


So...if the relay wasn't allowing enough power through to operate the pump at full capacity, you would have low pressure until the engine oil reached 4psi then the pump would have full power. The 4 psi would be reached by using starting fluid to fire the engine or can be achieved by an extended start time.

Which again is what I am seeing. I was able to start the engine today (it took a long time) without having to prime the engine. But it always takes an 'extended' crank time! :banghead:



How fast does the pressure bleed off? You should not see much of a change and it should hold pretty steady for at least ten minutes. If it doesn't hold that would indicate a leak. You said earlier that you haven't seen any signs of a leak.....it could be leaking and you wouldn't even know it, if it were leaking inside the intake you wouldn't know without looking inside or a bad pulsator would leak back into the tank with no external signs at all.

BTW you should take any advice offered by ricksza he is one of the smartest guys on here.

The pressure on the engine is holding 'fine'. It is not falling off quickly, and looks great. Note: 'Initially' I was seeing pressure fall off issues, but a few tonnes of injector cleaner, and that problem has gone away.

Bottom line, your pointing out the RELAY gives me an explanation for 'EVERYTHING' that I am seeing happen with the engine! I am going to look it all up, and start there. Good call DUDE!! :iceslolan

Regards,
----- Robb -----

thomasrn
03-10-2005, 05:17 PM
OK, the three relays in the Glove box are pretty darn warm! The connectors on all three have some 'brown ness'.

I pulled the fuel relay, and touched a wire across the contacts.

Fuel pump started running. Took a little longer running time. The pressure went up to around 60-65 PSI at which point I freaked, and pulled the wire (goin over pressure destroys a few other parts). Car started fine!

I swapped the relays around which didn't seem to help under normal starting conditions.

Tried pulling the Fuel pump relay, no fuel pump during start. No start.
Put the relay back in, started the car, pulled the relay, engine kept running. YUP - You're correct about the dual power sources to the fuel pump. GRRRR!

Quick trip up to the dealer, found they do not use that model of relay anymore. $33.00 for a new relay, may as well try it! It will be here tomorrow.

I'm also going to head up and get my VCM flashed with all the updates ( $40.00 bucks ). What the heck! The dealer is obviously doin me a bit of a favour on the VCM flash. This may give me access to a bit more of the engine through the autotap.

Regards,
----- Robb -----

BlazerLT
03-10-2005, 05:21 PM
Since when is 60-66psi abnormal for that truck.

blazee
03-11-2005, 09:37 AM
I hope the relay fixes your problem, but I have my doubts because of the "took a little longer running time". When the key is turned on, the pump only has 2 seconds to reach the proper pressure. If it took longer than 2 seconds for the fuel to reach 60 - 65psi using a jumper wire, more than likely the relay is not the problem. We would then be looking at a possible loose connection or loss of power on that circuit not allowing the pump to receive proper voltage or back to the original scenaro of a poorly performing pump or leak within the system.

thomasrn
03-11-2005, 01:21 PM
Since when is 60-66psi abnormal for that truck.

It's not. But if the pressure goes over 70 PSI, you really do a number on the fuel system. Which I think i've done, major smell of gas happening. Oh well, all that I need to do is drive it home, and pull it into the shop, the regulators going in this weekend.

Should I look at some kind of external engine cleaner before I take it apart? I seem to recall some sort of a foam that you spray on the engine, leave it sit, and then hose it off. Any thoughts?

Regards,
---- Robb ----

thomasrn
03-11-2005, 01:30 PM
I hope the relay fixes your problem, but I have my doubts because of the "took a little longer running time". When the key is turned on, the pump only has 2 seconds to reach the proper pressure. If it took longer than 2 seconds for the fuel to reach 60 - 65psi using a jumper wire, more than likely the relay is not the problem. We would then be looking at a possible loose connection or loss of power on that circuit not allowing the pump to receive proper voltage or back to the original scenaro of a poorly performing pump or leak within the system.

About the relay, I agree, but I'll swap it out anyway. One less possible problem!

I am planning to go ahead the the FP regulator install this weekend. I've got everything that I need, I'll be beginning on it tonight and on Saterday if I need something extra, I'll go grab it.

Thanks guys!

---- Robb ----

JRB Cobra
03-16-2005, 09:06 PM
About the relay, I agree, but I'll swap it out anyway. One less possible problem!

I am planning to go ahead the the FP regulator install this weekend. I've got everything that I need, I'll be beginning on it tonight and on Saterday if I need something extra, I'll go grab it.

Thanks guys!

---- Robb ----


curious if this fixed your problem. I now have the same prob you are having

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