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Online Wrench
Online Wrench, ASE Certified Technician
Category: Chevy
Satisfied Customers: 402
Experience:  ASE Certified, iATN Member, Asian & Domestic Specialist
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My truck cranks but wont start until i..throttle body..spark plugs

Customer Question

ok.... my truck cranks but wont start until i pour fuel down the throttle body, then it starts right up... it has a new fuel pump spark plugs cap and rotor... im lost idk what else to try.... its a 98 sonoma 4x4 SLS with a 4.3L vortec
Submitted: 5 years ago.
Category: Chevy
Expert:  Online Wrench replied 5 years ago.
Hello and Welcome to JustAnswer.com! When it starts after pooring fuel in the throttle body, does it stay running?
Customer: replied 5 years ago.
yes it runs just fine, just getting it started is the problem.... i was thinkin it was an ambeint air temp sensor maybe but idk...i thought to ask the experts in the feild
Expert:  Online Wrench replied 5 years ago.
Well the first thing you are going to need to do is get a hold of a fuel pressure guage. Obviousely we're looking at a fuel issue. So we need to see what the residual fuel pressure is at the time of the cold start. You can get a fuel pressure guage at most auto parts stores rather inexpensively. By the way....after you have the vehicle started, if you shut it off..will it start back up? Or do you have to prime it?
Customer: replied 5 years ago.
sometimes it does when its warmer out.... the fuel pressure regulator i put in it... its in the intake manifold and on the end its looks like its suppose to have a vaccum hose on it or something but it did have anything on there so im guessing it uses intake manifold pressure... and on of the O- rings on the regulator were broke right from the store so i didnt know if it was suppose to.... if it was would it do this?
Expert:  Online Wrench replied 5 years ago.
Your regulator should have a good o-ring on it. And there should be a vacuum line that runs to the intake manifold hooked to the regulator.
Online Wrench, ASE Certified Technician
Category: Chevy
Satisfied Customers: 402
Experience: ASE Certified, iATN Member, Asian & Domestic Specialist
Online Wrench and 7 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
but there is no line going to my regulator... the regulator is inside the intake manifold
Expert:  Online Wrench replied 5 years ago.
Ok. Have you ever checked fuel pressure with a guage? We need to do this before we go any further. You can purchas one at an auto parts store rather cheaply. Let me know what you find.
Expert:  Online Wrench replied 5 years ago.
Also, I will assist you until we get this problem solved. If we cannot get this problem solved, I will see to it that you are refunded.
Online Wrench, ASE Certified Technician
Category: Chevy
Satisfied Customers: 402
Experience: ASE Certified, iATN Member, Asian & Domestic Specialist
Online Wrench and 7 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
the pressure is 90 psi
Expert:  Online Wrench replied 5 years ago.

Ok. Is this with the key on? or the engine running? We need to know what the fuel pressure is at the time of a cold start. Follow me? So basically what we are looking for is , run the vehicle with the guage on....shut it off, let it sit for a period of time and then look at the guage before starting the vehicle.....what's the pressure? Make sense? Let me know.....sorry for the confusion. I greatly appreciate your patience and will do everything I can to assist you in fixing this problem!

Customer: replied 5 years ago.
so are you thinkin my fuel pump is bad or my fuel pressure regulator is the problem... cause my regulator is in my intake manifold and im guessing it uses intake manifold pressure to open the regulator... is it possiable the my upper intake manifold gasket is bad.... making it so it dont have the right vaccum to open.... and another question is it charging me 15 buck each time i ask another question????
Expert:  Online Wrench replied 5 years ago.

Ok. Quick lesson on how this works. Every time that you click accept....you pay the selected amount (in your case $15). You were only supposed to click accept when you recieved an answer to your question. Right now we are still working on getting the problem solved, so you shouldn't have clicked accept. It shows that you requested a refund, so the Moderators will contact you about clearing this up. Like I said before, I will help you with this until the end, so if you just want to make the ONE payment now thats fine. Or you can be refunded the full amount and you can pay me once we get this problem fixed. If you have any other questions about this, let me know and I will be glad to clear it up for you. Now back to the problem at hand.

The common problem with the situation you are describing is loss in fuel pressure after the vehicle sits. This is why I wanted you to take a fuel pressure reading after the vehicle has set for a while. Do you think that you could take this reading? Let me know.

Customer: replied 5 years ago.
yeah i does loose pressure when it sits there after it runs
Expert:  Online Wrench replied 5 years ago.
Ok. After sitting for a period of time....what does the fuel pressure drop to? Also....is this what your regulator looks like? graphic
Customer: replied 5 years ago.
yes thats what is looks like.... i dont remember what it dropped to... i borrowed the tester from the tech school im going to
Customer: replied 5 years ago.
can you also look and see if its suppose to have a vaccum line on there
Expert:  Online Wrench replied 5 years ago.
Ok. Well first off.....90PSI is TOO high. So I think there may be an issue with the regulator. But as far as the hard starting.....I think this is because of the loss in pressure. The regulator picture I posted.....the black end with the o-ring needs will stick into the fuel rail. The small tube on the side should have a vacuum line on it that runs to the throttle body. How was the old one? Please specify.
Customer: replied 5 years ago.
the o-ring on the end of was cranked and when i tested it i couldnt get the screen to move
.... so could you look and see if a vaccum hose is suppose to go on it or no
Expert:  Online Wrench replied 5 years ago.
The end with the o-ring needs to go into the fuel rail (the o-ring needs to be replaced if cracked or broken). The small tube that comes out of the side of the diaphram housing is supposed to have a small vacuum line attached to it that comes from the throttle body.
Customer: replied 5 years ago.
o really?? is there any possible way you could send me tear down pictures of it... casue when i took it apart the old one did have a vaccum line on it
Expert:  Online Wrench replied 5 years ago.
Ok.....I'm afraid that I cannot get you tear down pictures. There should be a small 1/4'' vacuum line that goes onto the small tube. This vacuum line should come from the throttle body. Trace it from there to the regulator. Should not be that hard to find. If you still can't find it, Start the engine and listen for a hiss from the open vacuum line.
Customer: replied 5 years ago.
so you can see pictures of it though.... cause its under the throttle body in the intake manifold.... its right off the lil box that my injectors go to
Customer: replied 5 years ago.
cause i cant run the truck and listen for a vaccum leak cause to get to it i have to have my intake manifold off
Expert:  Online Wrench replied 5 years ago.
I do not have a picture of this. This is a 1998 correct? With a 4.3L? Because I did not think that the Intake manifold had to be removed in order to get to the fuel pressure regulator.
Customer: replied 5 years ago.
yeah all that is correct 1998 4.3l vortec in a sonoma sls but i have to remove the intake manifold cause its under that in a lil box that my injectors connect to
Customer: replied 5 years ago.
i havent seen anything like this before and thats why im totally stumped
Expert:  Online Wrench replied 5 years ago.
Ok.....welll how about this. Start the vehicle and locate the vacuum line that is leaking. Then proceed to putting the vacuum line on the regulator. Make sense?
Customer: replied 5 years ago.
but how... its in the intake manifold and theres no vaccum line that are in my intake manifold... the only line there are the lines that go to my injectors... thats why i was thinkin that it opens by intake manifold pressure maybe...i was just seeing if that would make any sense at all because i tried lookin for a vaccum line in there for like two days and still nothin.... the old one didnt have one on there and looked like there hasnt been one on there causee there was carbon in the side that looks like there's suppose to be a line on
Expert:  Online Wrench replied 5 years ago.
Ok.....Was there a vacuum line on the old one or not? Because you keep changing your mind.
Customer: replied 5 years ago.
i said there wasnt one on the old on
Expert:  Online Wrench replied 5 years ago.

o really?? is there any possible way you could send me tear down pictures of it... casue when i took it apart the old one did have a vaccum line on it (Online) -- 2 Accepts / 2 Questions (2 Open)

 

This is what you posted earlier

Customer: replied 5 years ago.
sorry i meant didnt... i hate typing
Expert:  Online Wrench replied 5 years ago.
Ok. Did the old fuel pressure regulator look like the one in the picture I posted?
Customer: replied 5 years ago.
yes it did
Expert:  Online Wrench replied 5 years ago.

Ok. And does this engine have Sequential Fuel Injection-Injectors

or

Central Sequential Port Injection-fuel tubes to popet nozzles?

Customer: replied 5 years ago.
Sequential Fuel Injection
Expert:  Online Wrench replied 5 years ago.
Ok...then there should be vacuum to the regulator....end of story. Sequential runs a vacuum opperated regulator. CENTRAL sequential runs a spring opperated regulator. The picture I showed is of a vacuum operated regulator. So I think that you need to look into this.
Customer: replied 5 years ago.
but how is there suppose to be one when its under the intake manifold?
Expert:  Online Wrench replied 5 years ago.

I think that you have the two confused....I did some more looking into it. This regulator does recieve its vacuum supply from the manifold. So lets forget about this for now. Lets concentrate on cold start fuel pressure. Do you still have access to a fuel pressure guage? If so....lets take a cold start fuel pressure reading (after vehicle has sat). Let me know the results.

Customer: replied 5 years ago.
k... ill get it tomorrow
Expert:  GM Tech (Cam) replied 5 years ago.

There is no vacuum line running to the regulator simply because the regulator is under the intake manifold, surrounded by manifold vacuum. The pressure for this engine MUST be between 60-66 PSI pump running and engine off.

Customer: replied 5 years ago.
so if i had a bad upper manifold gasket it would case this to happen too
Expert:  GM Tech (Cam) replied 5 years ago.
No. You would have a racing engine if the upper intake manifold gasket was leaking. The next thing you need to deal with is the pressure. 90 psi is far too high and that leads me to think the return line may be plugged, or you have a bad regulator.
Expert:  Master Class Auto replied 5 years ago.

Hi MJ,

 

May I ask a few questions?

 

1) Is the engine (or ses) light on after you pour fuel into TB unit and successfully start engine?

 

2) How does vehicle run - after you manage to start engine by adding fuel? a) Runs well? b) Runs rough? c) Runs unusual, like I've never experienced before?

 

 

Best,

Master Class

Customer: replied 5 years ago.
the light is on but only because my O2 sensors are bad... well thats the only fault code that comes up... and once i get it running it runs good.... is there a phone i can call and talk to someone... my number is XXXXX
Expert:  Master Class Auto replied 5 years ago.

Hi MJ,

 

Your phone number is XXXXX out in your post. However, we can handle this right here. No worry. I'm very experienced. Please answer my questions. No run around.

 

Your check engine light is obviously ON. What are the exact code(s) ?

 

Best,

Master Class

Customer: replied 5 years ago.
i have the snap on diagnosic reader and it dont give me the numbers but it says like O2 bank lean.... ever since i put my dual exhaust on it like 4 years ago it always said that.... when i drive it around sometime when i go from a complete stop and hit the throttle it has a lil delay then goes but other than that it runs great... but also it only started to do that ever since i moved to wyoming cause im guessing the high elevation casue im origially from minnesota but im moving back there cause i graduate soon... idk its frusterating
Expert:  Master Class Auto replied 5 years ago.

Hi MJ,

 

Is your scanner able to read furl trim values?

 

Best,

Master Class

Customer: replied 5 years ago.
yes... what you thinkin might be wrong with it?
Expert:  Master Class Auto replied 5 years ago.

Hi MJ,

 

Sorry for previous typo. I meant 'Fuel Trims'. What is short term; S/T and long term; L/T fuel rim values?

 

Best,

Master Class

Expert:  Glenn replied 5 years ago.

Hello

 

THIS IS A DIFFERENT EXPERT.

 

I have posted a tip on your other post. I have posted this as a "info request" so as not to incur any additional expense to you. You can access this tip at

http://www.justanswer.com/questions/1m1il-want-money-back-last-question

 

Apologies to the other experts involved. Normally I would send an assist post but in this case I felt more direct action was called for.

 

 

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