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Disable fuel pump or just injectors for pressure test?


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Bumperbozo
User

Aug 26, 2017, 12:36 PM

Post #1 of 10 (418 views)
Disable fuel pump or just injectors for pressure test? Sign In

I'm shopping for a car, and I want to do a pressure test with the seller's permission on the car that makes it through the rest of my checklist. Do I need to disable the fuel pump, or can I just disable the injectors? Circuit opening relays are often near the ecu and require getting all up in the dash. I feel it would probably meet more objection than even taking out the spark plugs.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 26, 2017, 1:38 PM

Post #2 of 10 (412 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

What are you trying to do? Compression test?

What is the year, make, model and engine size?



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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.



Bumperbozo
User

Aug 26, 2017, 1:40 PM

Post #3 of 10 (408 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

Yes, compression test. Well, my current car is a 2.2 95 Celica GT, but I'm considering a V8 charger or a v6 Altima. Don't really know yet.Frown


(This post was edited by Bumperbozo on Aug 26, 2017, 1:41 PM)


Hammer Time
Ultimate Carjunky / Moderator
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Aug 26, 2017, 1:44 PM

Post #4 of 10 (402 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

Well, I can't tell you how to disable a fuel pump if you don't know what you are working on.



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

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.



Bumperbozo
User

Aug 26, 2017, 1:46 PM

Post #5 of 10 (398 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

That wasn't my question. I asked if I have to, or if I can simplify the task by just pulling the efi fuse.


Hammer Time
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Hammer Time profile image

Aug 26, 2017, 1:48 PM

Post #6 of 10 (394 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

Sure, you can pull the EFI fuse, if it even has one. Different systems work different ways. What is easy on one car may not even be an option on a different one.



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

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.



Bumperbozo
User

Aug 26, 2017, 1:51 PM

Post #7 of 10 (390 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

There's no danger in running the fuel pump with the injectors shut off and the starter turning the engine over?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 26, 2017, 1:56 PM

Post #8 of 10 (386 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

No, that wouldn't be a problem, depending how you did it. I wouldn't try unplugging injectors. If they have any age, the clips will start breaking. Killing the EFI would kill the fuel pump anyway.



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

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.



Bumperbozo
User

Oct 9, 2017, 1:57 PM

Post #9 of 10 (290 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

 
It seems like neither shops nor savvy car buyers bother with compression or leak down tests when buying a vehicle. Obviously, if there's a big compression problem, you'll get a misfire code, but if you have like 21% leakage across the board from ring wear, will that always show up as a code?


Discretesignals
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Oct 9, 2017, 4:56 PM

Post #10 of 10 (273 views)
Re: Disable fuel pump or just injectors for pressure test? Sign In

Really the only time you need to do a cylinder leak down test is if you find low compression. Some vehicles it is difficult and time consuming to perform a static compression test. Most people aren't going to drop big money into having their mechanic perform leak down test if there are no drivability issues or codes being set on a used car inspection. Even if there were codes and/or driveability issues, the mechanic would probably tell the customer there is an issue that the seller has to resolve and to look for another vehicle.

Leak down test won't tell you the condition of the oil rings anyway. If you are inspecting it yourself and you want to go through that, then cool. That's if the seller doesn't mind. Hard to say how much leakage it would take to cause misfiring. A better test would be a cylinder contribution test in my opinion.





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(This post was edited by Discretesignals on Oct 9, 2017, 5:05 PM)






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