Low Impedance vs. High Impedance Injectors

[ty20404]

So I'm chasing a rough idle in my Stroker and one thing that I've seemed to stumble across is that the injectors I have in there now are Siemens injectors (don't have the part number) that the PO of the engine gave me with it, that have a low impedance of about 2.7 ohms. I looked the number up online and it said they were 23 lb/hr but I'm afraid that the low impedance could be an issue. I'm getting a P0300 and P0301 right now, and I've been chasing rough idle issues for quite some time now as well as overheating which has gone away for the time being.

I've read conflicting information on the internet about the system on the 96 XJ on whether it is high or low impedance....

What impedance is my 1996 XJ???????? And why has my Jeep done over 10k miles just fine (aside from the rough idle) on low impedance injectors?

 

[Talyn]

You need high impedance

 

[ty20404]

Have some mustang 5.0 injectors (24#) on the way....

What would be some symptoms of running these low impedance injectors? Lean? Rough idle?

 

[Talyn]

I don't know what problems they would cause. Possible PCM damage, but not certain. It just shouldn't be done. Low impedance will require more amps to run.

 

[ty20404]

I'm kind of shocked nothing bad has happened yet but I will definitely be putting in the Ford 24#s.

I understand the impedance is going to cause a larger current flow from the PCM and could possibly damage it, but I'm curious to know if anyone knows more behind this and what exactly is going to happen to the injectors as a result... Will the system not be able to flow enough fuel? Will it not pulse correctly?

I can hear the injectors firing when I listen to them with a screwdriver, and I can definitley hear a slight mis when listening to the tailpipe even though it is intermittent but I'm just curious to know if this mismatch could certainly be the root cause of a lot of my problems.

 

[Talyn]

You have a mis and nothing bad is happening?

Make things as they should then diagnose. You can't properly diagnose when you have a variable such as this.

 

[yenkoz]

The low z injectors require more amperage to open. So your computer, which doesn't have the proper injector drivers won't be able to open the injectors the proper amount. Thus leaning out your engine due to lack of control, and possibly over amping(heating) your factory drivers and killling your ECM.

 

[ty20404]

The low z injectors require more amperage to open. So your computer, which doesn't have the proper injector drivers won't be able to open the injectors the proper amount. Thus leaning out your engine due to lack of control, and possibly over amping(heating) your factory drivers and killling your ECM.

This is what I was thinking... I really hope this is what's happening because that would explain some of the issues that I've been having or had happening. I won't jump to conclusions until I get the mustang injectors in there and I'll let y'all know. Well I'm just keeping my fingers crossed that nothing on the ECM is damaged.

 

[ty20404]

So I installed the mustang injectors and I'm not noticing a difference in my idle. It's still not right, somewhat rough and can hear a random misfire at the tailpipe with the smell of fuel.

What should my MAP reading be using a code reader? I'm getting between 9 and 11 "HG which from what I've read is low, but I can't seem to find the leak, have unplugged every hose going into the manifold and haven't gotten the idle to change.

When I first installed them and went for a little test drive my idle was significantly higher, like 1100-1200 and wouldn't go down until i unplugged the front hose coming off of the valve cover and plugged it back in. Could the valve at the back of the valve cover be causing this? I've replaced it with one from Advance Auto Parts and i know this piece is straight thru... Could that be causing the rough idle?

 

[ty20404]

Well, did a compression test. All cylinders were fantastic except for cylinder 1... Only 50 psi. Gonna pull the head, I'm guessing I blew the head gasket between the coolant passage and the cylinder. Got a fun day tomorrow!

 

[Talyn]

What should my MAP reading be using a code reader? I'm getting between 9 and 11 "HG which from what I've read is low,

Very low. 15-20 for a stroker, depending on cam and compression.

Could the valve at the back of the valve cover be causing this? I've replaced it with one from Advance Auto Parts and i know this piece is straight thru... Could that be causing the rough idle?

The valve at the back is the small one, about .060", not straight through.

Well, did a compression test. All cylinders were fantastic except for cylinder 1... Only 50 psi. Gonna pull the head, I'm guessing I blew the head gasket between the coolant passage and the cylinder. Got a fun day tomorrow!

Thats not good. Good luck. If you have an engine lift, pull the head and manifolds together... a lot easier.

 

[ty20404]

Pulled the head, cylinder walls looked fine so I went ahead and replaced the head gasket, torqued it down then did compression test again.... still 50 psi, so I'm thinking bad rings which would be the reason I probably had such low manifold vacuum.

Could I still have bad rings without any cylinder wall scoring?

 

[WB9YZU]

To diagnose low compression, you should get a spark plug to air hose adapter, and charge the cylinder with air.

There are 3 openings you want listen to for escaping air:
1) Crankcase (Oil filler hole)
2) Intake
3)Tail Pipe

1) Is caused by rings or a cracked piston
2,3 are caused by bad valve seating, bad valve, bad seat, cracked head, something holding a valve open, like a bad lifter.

-Ron

 

[Talyn]

Before you pull the head again do a leak down test. You aren't interested in figures so you can just pump compressed air in the cylinder and listen for the leak. Could be the valves or the rings or a crack in the block. Listen from the tail pipe for leaking exhaust valve, throttle body for a leaking intake valve, and oil filler or dipstick tube for leaking rings.

You might also consider a problem with the lifters and/or cam.

Did you take a look at the head and valves while it was off? Checked it for flatness?

 

[ty20404]

I am planning on doing a leakdown to pinpoint where the problem is. I did not check the head for flatness, but unless there is some significant curvature at the front of the head I doubt that is the issue considering every other cylinder was around 180 psi.

As for the cam/lifters, I can see them opening and closing as they should both from the top (rockers) and through the intake/exhaust ports in the head. When I had the head off the valves looked just as all of the others did and appeared to be closed just fine.

Regardless the leakdown should help me pinpoint the issue. I can pressurize the cylinder and just put my hand over the exhaust/intake ports to see if the valves are bad and just listen for air blowing down into the crankcase if the rings are the issue. My money is on rings however and I already have a new set ordered so if that is in-fact the case then I will be all ready to go.

 

[Hypoid]

A couple years ago, one of the Colorado guys had a head resurfaced. After reassembly, it ran like crap, had low compression on one cylinder. Turns out the machinist took enough off the cylinder head to hold one valve slightly open. The guy who figured that out shimmed the rockers enough to get the valves to seal.

FWIW...

 

[ty20404]

Well I went ahead and did a cold compression test again and the results came back as before... Cylinders 2-6 had 145+ PSI, Cylinder 1 only had 40 PSI.

Well obviously something was wrong with cylinder 1 and after I put some compressed air in the cylinder the most significant portion of leakage was definitely through the crankcase.

Pulled piston 1 and the top ring was cracked in half! I've got a replacement ring coming in tomorrow and will pick up a cylinder honing tool tomorrow as well. The bearings look great and everything else down below looks fantastic just as it did a month ago when I did the oil pump. Hope to have this thing running great again.

 

[Talyn]

How does the bore look? If there aren't any scratches then I wouldn't touch it with that tool. In the wrong hands that can do more harm than good. You really have to have a lot of practice to do a good job with that.

 

[ty20404]

How does the bore look? If there aren't any scratches then I wouldn't touch it with that tool. In the wrong hands that can do more harm than good. You really have to have a lot of practice to do a good job with that.

The bore looked great, honed it down with a 3 stone tool and got the whole cylinder to have a nice cross-hatch. Got it all put back together and it runs great now, smooth as can be and I can't hear a miss at the tailpipe. Honestly it's never run better since I got it so I think the guy sold it to me with it already having a compression issue.

Appreciate the help guys.