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4.3 ltr motor hesitates when you take off


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monty101
User

May 27, 2013, 5:21 PM

Post #1 of 26 (2457 views)
4.3 ltr motor hesitates when you take off Sign In

I got a 1997 blazer 4.3 ltr motor with 20k miles on a new motor and tranny

What should be the fuel pressure when I turn the key on?

It is now showing 60 lbs for 2 seconds while the pump primes. Then it drops to 55 and when
I turn the key to start it , it will jump to 60 and after it starts it drops to 52.

The problem is When I start it in the morning it revs ok but when I take off it acts
like it is not getting enough gas and hesistates. I pump the pedal and the pressure jumps
to 60 and I eventually make it to the stop sign at the end of the street and then when I take
of it runs fine. I think it is not getting enough fuel pressure. I have read in other threads that it
needs 60-66 lbs. Its getting 60 but it acts like that is not enough.

I have replacd the plugs, spyder injectors, and fuel filter. any help would be much appreciated.


nickwarner
Veteran / Moderator
nickwarner profile image

May 27, 2013, 5:33 PM

Post #2 of 26 (2441 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

When you replaced the pump, did you get a new updated connector to plug into the pump? Anything under 55psi will cause issues like crazy on a Vortec.If you installed the update plug, did you solder it or use butt connectors? Have you done a voltage drop test on the power and ground sides of the pump?


Hammer Time
Ultimate Carjunky / Moderator
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May 27, 2013, 5:34 PM

Post #3 of 26 (2441 views)
Re: 4.3 ltr motor hesitates when you take off Sign In


Quote
it will jump to 60 and after it starts it drops to 52.


That is a problem. This engine requires a minimum of 55PSI to run.



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monty101
User

May 27, 2013, 5:43 PM

Post #4 of 26 (2435 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

I have not put a new pump in it yet


monty101
User

May 27, 2013, 5:52 PM

Post #5 of 26 (2429 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Well it does idle at 52 then it jumps to 55 when i give it some gas and if I punch it it will jump to 59 and sometimes
it will jump to 60. After I go a block or so and stop and when I take off again it runs great

I've been told the gm book states it needs 60-66 lbs for the 2 seconds after you turn the key on and it seem to barely meet that requirement
as it gets up to 60. After it's primed the book states it will drop 5 lbs and when it starts up it will drop some more.

Question I got is I'm being told the gm book states the above. It appears to be borderline and I may be able to fix
my problem with the hesitation if I put a new delphi pump on it. I've read a new pump will jump the pressure up to 65 or so and solve a lot of problem s.

I don't really know if the pressure I am getting is normal and acceptable or if I need more. The range is quit big. 60-66. I'm definitely at the low end. I don't know if
the regulator will open up and keep it at 60 even if I do get a new pump and it puts out 85+ max pressure.......


(This post was edited by monty101 on May 27, 2013, 5:54 PM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 27, 2013, 5:55 PM

Post #6 of 26 (2419 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

No, it's not borderline. It's supposed to have 60 to 66 at all times when running or priming. It can life with 57, 58 but it can't live with 50 or 52



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monty101
User

May 27, 2013, 6:13 PM

Post #7 of 26 (2413 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

From what you are saying I need a new pump. If a new one gets me 65 when I turn the key on and it primes, the book states it will drop 5 after the prime is over and maybe 3 more when it is started up. that would drop it to the 57-58 range I guess which is a lot higher than 52. At least now I know the pressure regulator will not keep it at 60 even if the pump gets it up to 65. That would be a bummer. I'd be right where I am now pressure wise after spending 200+ for a delphi pump. Thanks for helping me.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 27, 2013, 6:16 PM

Post #8 of 26 (2406 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

I didn't say the pump was the problem, you did.

All I said is that below 58PSI is unacceptable. It's up to you to verify the cause.



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monty101
User

May 27, 2013, 6:42 PM

Post #9 of 26 (2398 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

There are a couple reasons I think I need a new pump. I got this truck from my son.
He said it needed a new spider because he said the poppets were always a problem.
He was wrong about that. It had already been updated with the latest spider that does
not have poppets. I put a new one in anyway......So, its got a new fuel regulator on it.

I put a new fuel filter so that is not causing a problem but the old filter was so plugged
up when i took it off I could not blow through it. I will acknowledge that the next day
after it had dried out i could blow through it but just barely.

I put new plugs in it. The old ones looked fine. they were tan.

It has not got a leak down problem as it holds the pressure for 30 minutes after you
switch it off.

I don't know what else could cause this problem and it appears that the pressure
is definitely low and the pump must be replaced either now in the near future and until it is replaced
it will never pump out 65 lbs of pressure.

Nothing I have done has caused this problem because my son said it was doing this before I put the
spider in or replaced the plugs and the fuel filter......

I think the fuel filter must have damaged the pump......

Believe me I kick myself for not knowing that the injectors were probably not the problem. That $200 bucks
I spent would pay for the new fuel pump. But that's my fault.

I just wanted to do my due diligence and at least ask you guys if the
65-66 lbs of fuel pressure was actually attainable with a new pump before I bought a new pump. Obviously
that may not fix my problem but I can't imagine what else could be causing this problem especially when
the pressure is low. I've check for air in the fuel line and I've even checked the tranny fluid level to make
sure the tranny shifting is ok and is not causing this hesitation.

If I am wrong then the facts are what they are., I made another bad decision but I have asked everyone I know
what to do before I decided to spend another 200 bucks on this truck.

If you know of any other things I can investigate please advise. the truck chassis has 220,000 miles
on it but it had a new short block and new tranny put in 20k miles back before I got the truck from
my son.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 27, 2013, 6:49 PM

Post #10 of 26 (2390 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

It sounds like you have done you due diligence and I tend to agree with you. The one test that would be helpful would be to pinch off the return line and see if the pressure spikes over 65PSI but most of the lines are plastic and shouldn't be pinched.



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monty101
User

May 27, 2013, 7:15 PM

Post #11 of 26 (2385 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Yeah, my feeling about pinching that line too. I think since the pressure regulator does not come at 60 if the pump was kicking out
more than 60 it would register it on the fuel gauge up to 66 anyway. It must be opening at 65 orr 66.

Thanks again for taking your time to dig into this with me. I got my fingers crossed this fixes it. I got to drive it some to get rid of
the 20 bucks of gas but in todays world 20 bucks is not very many gallons to deal with. I'm actually surprised it runs at 52 lbs. I have noticed it
actually idling at times when the pressure gauge showed only 48 lbs of pressure for brief periods of time.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 28, 2013, 4:57 AM

Post #12 of 26 (2366 views)
Re: 4.3 ltr motor hesitates when you take off Sign In


Quote
The one test that would be helpful would be to pinch off the return line and see if the pressure spikes over 65PSI but most of the lines are plastic and shouldn't be pinched.


Come on now..Don't go pinching or putting shut off valves on the return line with the pump running unless you want to take a chance of blowing out the diaphragm in the regulator. They are not designed for that kind of pressure.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


monty101
User

May 28, 2013, 8:11 AM

Post #13 of 26 (2353 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Well i called Delphi this morning and talked to their tech. He said the injectors I bought from the check at 60 and I will never have more than 60 lbs of pressure.
He said when i switch on the key and not start it the pump should prime at 60. He said the pump is rated at 61 1/2-62 lbs of pressure when it primes and the
regulator will return the gas to the tank at 60. He said if I pinched the hose it would pump out lots more pressure. He then told me that after it primed it could drop to 45
and it could also drop to 55 like mine does and when it is running it should be running with about 52 lbs. He told me to check the volumn of gas by taking my schradder
valve hose connector loose from my gauge and attach it to the fuel line and see how long it takes to pump out a pint of gas. If it pumps out a pint in 15 seconds then
the pump is pumping enough gas to run the motor ok. Mine pumped half a pint in about 10 seconds.

I have no idea what to do now. I will just drive it and hope there was air trapped in the gas line somewhere and it will stop hesitating sooner than later.

I called Rockauto and had them cancel the order I placed online last nite.


Hammer Time
Ultimate Carjunky / Moderator
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May 28, 2013, 9:19 AM

Post #14 of 26 (2348 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

OK, I back out of here and you make your own decision. I'm not going to get into a debate with the pump manufacturer but they are flat wrong.

You have a bypass regulator that releases at pressures between 60 and 66PSI, depending on vacuum. The pump should be capable of higher than that at all times.

I'm sure DS has more answers for you.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



monty101
User

May 28, 2013, 12:59 PM

Post #15 of 26 (2336 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

I just put some alcohol in the tank. I guess if there is water in the tank it could cause the problems too.
I'm going to double check and call another mfg and see what their spider fuel regulator check is set to
open.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 28, 2013, 1:12 PM

Post #16 of 26 (2333 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

That's a good way to take out the whole fuel system.



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monty101
User

May 28, 2013, 3:34 PM

Post #17 of 26 (2325 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

I pulled the rotor, it was white and way past being useful anymore. I suspect it was not the
gas after all it may have been poor spark. I noticed with the new rotor and cap that it seemed
to still have a slight miss when you reved it. So, I also put on new plug wires and it
may be fixed now. No more miss and starts better. We will see...... I put the alcohol in to get rid
of any water in the tank. the alcohol will mix with any water and cause the water to hopefully
evaporate tonite.

Again thanks for all the help... I got a lot of respect for the knowlege you guys have
that I lack. I'm getting better, I have to. Got 4 vehicles that have over 220,000 miles on
each of them and I have a 5th that has 150k miles on it and I gave my daughter one that
I keep going that has 85k miles on it. I really hated to give that one up. all are paid for
and all but one are insured and driven. I decided to park my old 1989 Jimmy, its in good shape
but I really don't need it since I got this blazer. I may sell it. Only has 100k on the motor and
tranny. its a 4wd too.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 28, 2013, 3:40 PM

Post #18 of 26 (2320 views)
Re: 4.3 ltr motor hesitates when you take off Sign In


Quote
I put the alcohol in to get rid
of any water in the tank. the alcohol will mix with any water and cause the water to hopefully
evaporate tonite.


I'm fully aware of what alcohol does.
First off, nothing evaporates in a closed fuel system.

I'm also aware that it will eat rubber and will destroy about every piece of rubber in your fuel system and after it does that, the pieces if rubber will get caught in everything, up to and including the injectors.

Alcohol has not been recommended since cars started using fuel injectors.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on May 28, 2013, 3:41 PM)


monty101
User

May 28, 2013, 5:32 PM

Post #19 of 26 (2302 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Interesting about the alcohol. My wife is the one who told me to put some alcohol in it to get rid of the water. Sounded like a good idea and I did it. Guess I screwed up.
I drained the tank after reading your posting. I was not trying to educate you on alcohol. I was just trying to tell you why I put it in. Sorry you got upset.... Thanks
again for the advice. Like I said i do not pretend to know as much as you guys but I am learning.

The gas that came out was not even the same color as the fresh 5 gallons I put back in. it was not as clearkinda yellowish......I don't know what was in that old gas but I suspect it had a lot to do with why the blazer was having problems getting untracked every morning. Now its got fresh gas, new distributor cap, new rotor, wires and plugs and a new spider and fuel filter. Hopefully if will go down the road ok now.

I did call another mfg. I called rockauto and they told me to call ACDelco and their tech told me the best he remembered back when GM was devising ways to get rid of poppets he thought that gm decided to keep the regulator valve opening at 60. he told me to call a GM dealership. So, maybe the pump will do the job. He said they probably have a range of acceptable levels of gas pressure to make it clear that the pump will work even if the regulator is out of spec and allows the gas pressure to go up to 66 lbs. He said if the valve is in spec it will pump up to 60 lbs., just as mine is doing. I definitely know there are a lot of mechanics out there that say it needs to run at 60-66 and if that is true my blazer will not run right until I replace the fuel pump and if I have to I will get a new one. I think I've exhausted all the remedies that I have been advised to take to fix this truck. time will tell


Hammer Time
Ultimate Carjunky / Moderator
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May 28, 2013, 5:40 PM

Post #20 of 26 (2297 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

I have dealt with many, many Vortec fuel systems and I can tell you positively that when the pressure drops below about 57 PSI, driveabilty problems begin, usually in the form of high speed surging and hesitation and hard starting in cold weather.

There is no reliable tech in the world that will tell you that 52PSI is acceptable in a Vortec.

Alcohol used to be commonly sold as Dry gas and recommended to remove water in fuel back in the carburetor days but not in the past 20 years.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on May 28, 2013, 5:41 PM)


monty101
User

May 29, 2013, 9:28 AM

Post #21 of 26 (2275 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Think I finally caught the problem and yes you are correct. I should expect that this should not surprise you. I figured you were but i wanted to be sure because I didn't want to buy a new pump and find out I didn't need it. It won't run right at 52 lbs of pressure. I knew it would dropp to 52 but it would jumping back to 55-60 when I pushed down the pedal and drove down the street when i had checked it. I finally caught it staying at 52 when it was doing its hesitation act. I figured you were sick of my problem so i swithed to another forum. Here is what i sent the tech about what i discovered this morning. I had told him I thought the new wires, dist. cap and getting rid of the bad gas would fix the problem. I sent him this because I was wrong:

"Unfortunately I still got the problem. I put my fuel pressure guage on it and ran the hose up through the hood so I can monitor the pressure when the blazer is driven. After it is primed in the morning at 60 lbs, for 2 seconds the pressure drops to 55 and then when i put it in gear it drops on down to 52 and sometimes it stays there when i try to back out into the street and drive up to the corner even with me pumping the accelerator pedal trying to coax it along. I know this is weird I thought when you give it gas it's supposed to lower the vaccum which should increase the fuel pressure. This does not happen when the pressure is 52 even though the motor is revving while its hesitating along as I drive it up the street. It barely makes it to the corner stop sign but then when you take off the pressure will be at 52 idling but it will immediately jump to 60 and drop to 55-58 after i get up speed. No hesitation. I shut her down and the pressure was 48 and then it rose to 58 and after 10 minutes it dropped to 55 and then 4 minutes later it dropped to 50. It will eventually drop to zero by morning.

What is causing this morning hesitation and low pressure. Is it the pump? Is it air in the line? I've driven it all over since I drained all the bad gas and replaced it. So, I don't think its air in the line. The fuel regulator is new since I just put a new delphi sprider on it and a new fuel filter. I called Dephi and they said the pressure regulator is set to check the pressure at 60 and that is what it is doing, So, I don't think its the regulator. I'm thinking I need a new pump. If it was the regulator it would do it all the time. The pump may not be doing this all the time only because it gets heated up after it has run awhile and the heat makes the moving parts expand to take up space created inside it because it is worn out. Everyone says they won't run on less than 55 lbs of pressure. Mine runs ok at that pressure but as I've said early in the morning it won't get that high until I drive it up the block to the first stop sign. Then it runs great......"


(This post was edited by monty101 on May 29, 2013, 9:42 AM)


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 29, 2013, 10:12 AM

Post #22 of 26 (2270 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Yes, you're going to need a new pump. Regulators just don't act that way. They are designed to restrict flow to 66PSI at low/no vacuum and release to 60 with full vacuum. The pump needs to be capable of more than 66 at all times. It's just a spring loaded variable check valve.

You said earlier that you had a restricted filter and that will take out a pump every time.

I am shocked that the Delphi people were so misinformed about this vehicle.

Let us know how it turns out.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on May 29, 2013, 10:13 AM)


monty101
User

May 29, 2013, 2:58 PM

Post #23 of 26 (2246 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

Just realized one of the 5 vehicles I got is a 96 sonoma that had a sprider just just like the one
I just put in the Blazer put in last year along with a new fuel pump. I put my pressure gauge on
it turned the key to prime it and cranked it up and it registered 66 on prime and 57-58 running. So much for asking Delphi
and thinking it was supposed to prime at 60 and had a regulator that released at 60....

Add that 5 pounds(65 lbs Sonoma-60 lbs my Blazer=5 lbs. ) to my running pressure at 52 and you get 57. My pump is worn out and
pumping 5 pounds less than it should. Gonna order that delphi pump again tomorrow. That Sonoma even
had a little pressure in the line too. Its been setting out front and has not been started in a week. Guess
mine may not leak down to zero like it does now if I put a new pump on it.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 29, 2013, 3:05 PM

Post #24 of 26 (2242 views)
Re: 4.3 ltr motor hesitates when you take off Sign In


Quote
My pump is worn out and
pumping 5 pounds less than it should.


It's a lot more than 5 lbs light. A good pump is capable of 70 to 80PSI if dead headed. It stops at 66 because the regulator releases everything above that.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



monty101
User

May 29, 2013, 6:29 PM

Post #25 of 26 (2228 views)
Re: 4.3 ltr motor hesitates when you take off Sign In

do you think a new delphi pump is the way to go? I am kinda concerned after that Delphi tech telling me
it would only prime it up to 60 lbs after seeing that '96 Sonoma which would need the same model pump
prime up to 66. He even said 52 lbs was ok. He said it might even drop to 45lbs.

Bottom line is will a delphi put out 66 lbs of pressure. I'm thinking I may need to
consider a acdelco instead. Don't know if you can make any brand recomendations but maybe you can tell me which brand of pump
have you used in the past that put out 66 lbs when it primed a 4.3 motor??






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