combustion gas in fuel rail

Brad Clayton · July 26, 2009

I came across and interesting way to see if combustion gas is getting in the fuel system. It was purely accidental and I decided to snap a quick video to try and show ya'll. When ever I have a driveability concern on a 6.0l, I use the new WOT simulator fuel pressure gage. It's easy to hook up and I think it works quite well in conjunction with the 5 gage bar setup to verify fuel pressure problems.

First I hooked up the tool to the secondary fuel bowl tap.

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With IDS loaded and the valve shut on the tool, the engine is ready to start.

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The engine runs, but runs poorly to say the least as indicated by the power balance screen.

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With the valve open on the tool, the pressure is well below spec.

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As the engine was running and I was monitoring all this stuff I noticed this.....

The bubbles are alot easier to see live and in person. But you can get the idea. The fuel actually pulses like a heart beat as it flows through the hose. My boss wanted me to get the fuel pressure to spec. before doing anything. I replaced a faulty fuel pressure regulator and got the pressure up to 58 psi.

Now it's time to dive into the right bank of the engine.

Keith Browning · July 26, 2009

I discovered this too when the tool first came out. Basically it is the dynamic version of the compression bubble test or the balloon test. Obviously it wont work on engines that don't run but sighting bubbles in the flow tester tubing is a great way to confirm combustion leaks on the ones that do. Great job with the video Brad! (I do wish it was in focus though)

Aaron · July 26, 2009

Works best on an E-series, because you're tapped directly into the back of the head that has the bubbling issue.

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Keith Browning · July 26, 2009

You mean IF you are tapped into the head that has the problem.

Aaron · July 26, 2009

This is true...but if you're worried about it, why not check 'em both? Posted Image

Brad Clayton · July 26, 2009

Usually, if there is a problem like this, the power balance will pick it up and lead you to the problem side.

Aaron · July 26, 2009

Usually, if there is a problem like this, the power balance will pick it up and lead you to the problem side.

Also a good point, Brad!

Keith Browning · July 26, 2009

Usually, if there is a problem like this, the power balance will pick it up and lead you to the problem side.

Correct.

Bruce Amacker · July 26, 2009

Brad:

Excellent documentation and demonstration of a great concept! Don't you have something going on with cyls 4 and 7, though? Here's a slide I use in class from a leaking (loose) injector killing a bank:

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Brad Clayton · July 26, 2009

This truck is beat and has many problems to say the least, Bruce. It defenitely wont be a cut and dry repair. But someone has just replaced all the odd side injectors and now this is going on so I am going to get that side back apart and have a look-see.

Aaron · July 27, 2009

Brad:

Excellent documentation and demonstration of a great concept! Don't you have something going on with cyls 4 and 7, though? Here's a slide I use in class from a leaking (loose) injector killing a bank:

Nothing's wrong with that truck. That's the new 6.0 'Displacement On Demand' system at work to help save fuel.

</satire>

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Brad Clayton · July 27, 2009

Cadillac came out with that a while back, no? It turned a 8 cylinder into a 4 cylinder, if I remember correctly. I don't think it worked for them either. Posted Image

STROKER_T · July 27, 2009

So I think the answer is,the passenger side has really low or way too high of fuel pressure,maybe even a broke or missing copper washer or combustion leak inside injector,and the driver side is cutting fuel...what about an oil leak on that side?(1,3,5,7)

Seen that balance scenario a few times,almost always fuel pressure being low...

So Bruce,what is the politically correct answer by the way?... Posted Image

Brad,thanks alot for the step by step on that,it is much appreciated.. Posted Image

Bruce Amacker · July 27, 2009

Seen that balance scenario a few times,almost always fuel pressure being low...

Yep, probably.

So Bruce,what is the politically correct answer by the way?...

8 new Alliants from Larry and a new HFCM.

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Jim Warman · July 28, 2009

Originally Posted By: Brad Clayton

Usually, if there is a problem like this, the power balance will pick it up and lead you to the problem side.

Correct.

The power balance will pick it up and lead you to the obviously worse side... Let's not forget that this is a "relative" test - not an "absolute" test. Granted, if both sides have a problem, there is every chance in the world that the truck plain wont run... but I haven't lived long enough to have seen quite everything, yet...

Also... a PB ahowing a concern on one bank can only 'suggest' a combustion gas in fuel rail concern... only now we have a "better" next diagnostic step - one that will prove or disprove the assumption.

Brad.... Cadillac called it the 4 - 6 - 8 modulated displacement engine. It didn't take long for the dealers to install a switch in the cubbyhole to turn the "feature" off.... Turned out the system worked more like a 3 - 5 - 7....

G'day... I'm Jim - I'll be your devils advocate for this evening.....

slim · July 28, 2009

The fuel pressure tester would also show bubbles if there is a leak on the inlet side of the pump. I guess you could check fuel flow with the engine off and then with the engine running to see if it's a leak or combustion gas.

Bruce Amacker · July 28, 2009

I had a 6.0 a few years ago (relatively new, still under warranty) that was at the dealer several times for performance complaints. It turned out to be a bad HFCM aerating the fuel internally intermittently. I took it apart and could not find the fault, but a new HFCM fixed it. It was a MF to diag due to the intermittent nature of the complaint, we ended up with inlet and outlet buckets and lines proving it was aerating. Perhaps the auto-bleed nature of the secondary FF was just barely enough to get rid of the air generated.

Any source of air will show up in the return line, but if the cyl balance graph shows misfires only one one side, you could probably bet it's an injector.

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Brad Clayton · August 23, 2009

Well this one is fixed, sorry for the late reply.

Quote:

Don't you have something going on with cyls 4 and 7, though?

Quite right on that one Bruce, it turned out to be a tank delamination!

I was having a difficult time with this one, seeing how another dealer had just put 4 injectors in for the same problem. Unfortunately they didn't get to the root cause.

SYMPTOM

SYSTEM

COMPONENT

CAUSE

This idea may not have made to their dealer yet.

I did some lookin' around on here and luckily the truck had a dump body on it. So after removing the right side injectors and replacing a bad cup in the number 1 hole, I removed the left side injectors. They were rusted wicked bad between the o'rings for the fuel inlet. Posted Image

After removing the fuel sender it was quite obvious what the prob was. I replaced the tank and sender and HCFM, finished up with the injectors and a number 4 cup and all is well.

Truck was an '07 with less that 35k on it.