tii air bubbles in KF line

[Get2theBimmah]

Hey guys,

 

I noticed the car misfiring a bit and not running very smoothly last time out.  I see that just cylinder 3 KF clear line has air bubbles passing through it into the injector.  The KF was rebuilt about a year ago along with the injectors being refreshed themselves.  Tried searching around here, but didn't come up with anything.  Any ideas of where to go to next? 

 

 

[bergie33]

I would contact the rebuilder. They should have some idea what could be causing that. Especially if it's something internal like a suction or delivery valve. 

[Son of Marty]

I would check the fuel hose between the tank and fuel pump air must be getting in on the suction side after the pump it would leak fuel.

[Get2theBimmah]

53 minutes ago, bergie33 said:

I would contact the rebuilder. They should have some idea what could be causing that. Especially if it's something internal like a suction or delivery valve. 

 

Yeah, I put the feeler out with him for insight. 

 

52 minutes ago, Son of Marty said:

I would check the fuel hose between the tank and fuel pump air must be getting in on the suction side after the pump it would leak fuel.

 

Tank down to the pump under the car is dry.  If the feed is allowing air in, wouldn't it be across all 4 lines of the KF?

[williamggruff]

Also possible there’s a small crack in the #3 plastic fuel line, though I’d expect you’d see fuel misting from the site of the crack. 

[dlacey]

Given those lines are normally running at 350-550 PSI, i would guess if you see bubbles there must be no pressure in that line [air bubbles would be compressed to nothing at 500psi]. It could be as simple as a stuck delivery-valve on the pump head....if thats stuck open then after the injection pulse the line would immediately return to fuel pump pressure ~30psi. Go thru the 'warm running problems' section of the Blue Book, try swapping the delivery valve to another cylinder, see if problem follows.

[SydneyTii]

3 hours ago, dlacey said:

try swapping the delivery valve to another cylinder

+1 Great advice!

[Son of Marty]

3 hours ago, dlacey said:

Given those lines are normally running at 350-550 PSI, i would guess if you see bubbles there must be no pressure in that line [air bubbles would be compressed to nothing at 500psi]

But with air in the pump you're not going to be able to build that kinda pressure. I agree with switching the valves to see if the problem changes cylinder.

[Get2theBimmah]

On 2/12/2023 at 5:51 PM, williamggruff said:

Also possible there’s a small crack in the #3 plastic fuel line, though I’d expect you’d see fuel misting from the site of the crack. 

 

Yeah good thought for sure, I don't see anything goin on there. 

 

23 hours ago, dlacey said:

Given those lines are normally running at 350-550 PSI, i would guess if you see bubbles there must be no pressure in that line [air bubbles would be compressed to nothing at 500psi]. It could be as simple as a stuck delivery-valve on the pump head....if thats stuck open then after the injection pulse the line would immediately return to fuel pump pressure ~30psi. Go thru the 'warm running problems' section of the Blue Book, try swapping the delivery valve to another cylinder, see if problem follows.

 

That's a good thought.  I hope not as it was recently refreshed.  I'll try swapping the delivery valves and see how that goes.  In the same vain, I can also swap injectors too and see if it follows.  One thing at a time to be able to rule it out.  Plus I don't feel like digging in there around the plastic elbows unless I really have to.

 

[dlacey]

Be careful about over-tightening the unions on the pump and injectors... The check valve body can split, ruining your whole day.

[Get2theBimmah]

On 2/13/2023 at 8:42 PM, dlacey said:

Be careful about over-tightening the unions on the pump and injectors... The check valve body can split, ruining your whole day.

 

Oh yeah for sure.  Going to trouble shoot this weekend if time allows.  The KF rebuilder is leaning on injectors being the problem and told me to start there first.  Will report back with the findings. 

[TobyB]

Quote

I can also swap injectors too

That's what I was thinking- if it's only one, and it's not murdering you with high pressure fuel,

its residual pressure valve may be stuck open.

 

t

 

Edited February 15, 2023 by TobyB

[mvliotta]

+1

 

I had a similar problem AFTER I got my injectors serviced. One of them came back stuck closed. Swapping injectors proved that to be the case. The outfit that did the service fixed the issue and all was well. 
 

Vince

[thehackmechanic]

Absolutely, check the injector. I had a similar problem years back with a friend's car—not bubbles, but #4 line just had a different look to it than the others. When I disassembled the injector, I found a broken spring.

 

[Get2theBimmah]

Thanks for the recommendations and suggestions guys.  Swapped injectors and the air followed confirming the injector to be faulty.  The rebuilder is sending me out a replacement no charge and I will send mine in to him.  Also ordering another refurbed set from him to keep before they become unobtanium.