fuel pressure check for leaking injectors

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fuel pressure check for leaking injectors

Postby OrlandoSonomazr5 » Sat Jul 11, 2015 2:23 pm

so my engine has a serious misfire only at idle up to about 3000rpm then runs good

We've gone trough all the basics distributor, wires, plugs, cleaned maf, checked map and maf sensors.

During fuel injector test your supposed to turn engine to on position get around 55lbs of fuel pressure and then it should drop when you start motor about 4-8psi. Mine dropped 2psi.

Than when you shut the motor off it should keep fuel pressure for about 1 minute than bleed off, It should be bled out completely after 5 mins.


Mine is not dropping fuel pressure even after an hour of being shut off. Its still showing 58lbs of fuel psi.

Im also noticing a huge difference in numbers between my ST and LT1 and 2 banks numbers are way off from each other.

My question is could the fuel pressure regulator be stuck and only starting to function once enough vacuum is formed inside the manifold forcing it to start working.
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Re: fuel pressure check for leaking injectors

Postby HenryJ » Sat Jul 11, 2015 7:24 pm

Sounds reasonable. Have you checked your vacuum? Could it be weak , or have a leak?

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Re: fuel pressure check for leaking injectors

Postby LoneWolf04 » Sun Jul 12, 2015 7:57 am

I have never seen these motors bleed off completely in 5 minutes unless you have an issue with something leaking or a bad pressure regulator. Sounds like you are having normal fuel delivery operation.
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Re: fuel pressure check for leaking injectors

Postby OrlandoSonomazr5 » Sun Jul 12, 2015 12:35 pm

Have checked for fuel pressure leaks and like I said gauge remains stable for well over an hour so no bleed off. Only possibility is if one of the poppet valves in the old fuel injection is having a issue.

We checked all spark plug wires to make sure ignition pulse was constant and equal to every other cylinder and the light blinked/pulsed the same for each spark plug. So we know ignition is not the issue.

Fuel pump is working, fuel filter is brand new.

Seems to run a bit better when a little starter fluid is sprayed in, but to much kills the motor.


I did just fix my exhaust as it had a leak just after the cat. Could the cat be clogged and the now added back pressure becauseing the o2 sensors to go crazy cause as I stated one bank is definitely running lean.

Wideband in exhaust at idle warm shows 20:1 above 3000rpm drops back to 13:1/14:1
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Re: fuel pressure check for leaking injectors

Postby OrlandoSonomazr5 » Sat Jul 18, 2015 11:48 am

So I tried an old trick called the Dollar bill trick and the results were unfortunate.

It seems I have a possible stuck valve or possibly bent either seems the heads need to come off. Totally bummed about this, only had it for 6 months and I've dumped more money into this truck than my other 3 vehicles combined.
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Re: fuel pressure check for leaking injectors

Postby OrlandoSonomazr5 » Sat Jul 18, 2015 6:55 pm

so compression checked revealed 210 across all 6 cylinders. I'm assuming a bit high from the the normal 180lbs from carbon buildup in the cylinders.

But we did find that disconnecting cylinders 3 and 4 had absolutely no effect on the motor other wise meaning they are not forming combustion.

Now for the reason why. We have spark, we possibly have air we possibly have fuel as one of the spark plugs was very rich while the other was very lean.

I'm beginning to think I have collapsed lifters so i'll be removing the valve covers to inspect the valve train for any issues. hopefully its something that stupid. Or We find that were not getting fuel and it needs a new spider fuel injection system.

Bottom line slowly but shortly we are narrowing down the issue.
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Re: fuel pressure check for leaking injectors

Postby OrlandoSonomazr5 » Sat Jul 25, 2015 9:34 am

Replaced old CSPI Fuel Injection with the new style and now have a no start issue.

Can't win with this thing.

Anyone bored who can take some photos around the top of their motor for me. I have two nuts left and can't figure out where they go.
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Re: fuel pressure check for leaking injectors

Postby LoneWolf04 » Sat Jul 25, 2015 10:01 am

If it's a crank no start I'm guessing the distributor is a tooth off.
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Re: fuel pressure check for leaking injectors

Postby OrlandoSonomazr5 » Sun Jul 26, 2015 2:01 pm

distributor never came out when changing the fuel injection system and it ran before. We have spark. It seems to be a fuel issue.
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Re: fuel pressure check for leaking injectors

Postby Built2Bend » Fri Jul 31, 2015 10:36 am

Is it possible you have a couple wires switched? I know it sound stupid but I've seen master techs do it by acident before. Good luck with your truck I hope it all works out.

I got a funny story kinda simalar.

When I did my head gasket on my 4cyl s10 I bent a pin in the plug for the fuel injectors it plugged back in Fine so I dident notice it when I went to start there was a crank with no start and it sounded Terible almost like a knock I Thot one of my push rods wasent in the rocker still while I was pulling the valve cover to check I found the bent pin. That's just something to think about I'm sure there totaly diferent.

Also if you are goiNg to need to pull the head off I have a brand new set of felpro head bolts and a head gasket set(gaskets are only missing the intakes) I bought all of it just I case.
1995 s10 reg cab short bed 4 cyl stick (sold)
1998 s10 reg cab short bed 4 cyl auto
2004 Sonoma crew cab v6 auto
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