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Troubleshooting w/ Vacuum Gauge- where to go from here?


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Looking for some guidance, suggestions and solutions.

Vehicle info:
1978 L28E
Rebuilt motor, internals unknown, mileage 180,000

Tested everything FI bible related, all passed.
New battery.
Cleaned all electrical connections, checked all hoses for tears/splits/etc.
AFM idle bypass not calibrated per altitude or emissions, adjusting in or out full makes no changes.
New plugs, wires, cap and rotor.  Distributor set form previous owner, not turned, set or checked.
Fresh fuel and filter, lines purged.

First compression test, mildly warm motor, ambient air 35°F, cylinders 1-6: 185,190,190,190,195,190
This seems impressively high, but I'll take it as I thought it was going to be low and inconsistent.
Plugs are all black soot to oil fouled, running rich rich rich since purchase.

Vacuum Cold Start:

http://www.youtube.com/watch?v=eNxDt7UzAoM

Vacuum at Idle and blip of throttle:




Haven't popped off the valve cover yet, checked/adjusted timing, or if motor is even TDC from previous owner/rebuilder.
Due to it being rebuild I want to get a baseline before going off the edge and pull everything apart..

Hopefully once I pull the cover the rest of the head looks this clean:

IMAG0178_zps768fe482.jpg


So where to go from here? Edited by AdreView
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Why do you think you have a vacuum leak???...

 

Its easier to find a leak with Carb spray, Brake Kleen, or even Starting fluid. You don't have to spray anyting until its soaked to check for a leak, just spray it lightly and quickly. If the idle increases or decreases when components are sprayed, that's where your leak is.

 

Check your fuel pressure regulator, cylinder head temp sensor, cold start injector, and efi relays.

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AFM bypass not calibrated, adjusting makes no changes.

 

What does the above mean?  And what are you adjusting?

 

The vacuum gauge doesn't do you much good with the idle speed jumping up and down.  The weird idle could be from a loose, undamped AFM vane, causing fuel enrichment to jump up and down.  Check that the weight is still attached, they've been known to fall off.  Or the AFM spring is so loose (maybe too much adjustment) that the vane is bouncing around.  Take the cover off and hold the counterweight and see if idle stabilizes.

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Why do you think you have a vacuum leak???...

 

Its easier to find a leak with Carb spray, Brake Kleen, or even Starting fluid. You don't have to spray anyting until its soaked to check for a leak, just spray it lightly and quickly. If the idle increases or decreases when components are sprayed, that's where your leak is.

 

Check your fuel pressure regulator, cylinder head temp sensor, cold start injector, and efi relays.

 

I "believe" I have a vacuum leak, I'm not certain.  Troubleshooting with the vac gauge is quite common after diagnosing all the FI related equipment, I'm going through the entire process.

I'm hesitant to spray fluid all over the motor, smoke seems like a cleaner/safer way as SDgoods stated.

 

I have not checked the fuel pressure regulator, since the fuel pressure is fine, I'll go here next.

Temp sensor, cold start and EFI relays passed with the FI bible testing.  I did disconnect the cold start and no change to idle.

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If you can find a shop or a friend with a smoke machine, they work great

 

I don't have access to this, however I may try with the use of a cigar!

 

Smoke machine would help me with determining which seals around the doors, hatch and windows require replacement.....I may look for one now.

Edited by AdreView
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What does the above mean?  And what are you adjusting?

 

The vacuum gauge doesn't do you much good with the idle speed jumping up and down.  The weird idle could be from a loose, undamped AFM vane, causing fuel enrichment to jump up and down.  Check that the weight is still attached, they've been known to fall off.  Or the AFM spring is so loose (maybe too much adjustment) that the vane is bouncing around.  Take the cover off and hold the counterweight and see if idle stabilizes.

 

The AFM bypass screw adjustment had been tampered with prior to me taking the vehicle, no plug was on the AFM either and it may have been clocked as there is some apparent tampering with the guts of the unit.  I know its purpose and made some adjustment to ensure it was not open or closed all the way.  The Z is not subject to emissions or smog here in IL, so no worries of getting her dialed in for testing at a facility.  

 

The AFM is complete, cover removed and all components checked in.  Weight is there, but tampering is evident.  I have 2 more used AFM's which I tested per the FI bible and neither one is in passing condition.  They all look used and tampered with, nor do they make a difference with the jumping idle.

 

I have not held the counter weight to see if it makes a difference. 

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Well, good luck with it.  Engine RPM can be affected by three things - air supply, air/fuel ratio, and timing.  Timing is a possibility but if you had your vacuum advance connected to full-time vacuum I would have expected idle speed to increase and stay high.

 

Engine speed affects fuel pressure through the FPR vacuum hose, and timing advance through the advance diaphragm.  Maybe disconnect those things, then start the engine and see if fuel pressure varies, or behavior changes.

 

 

Here's an odd possibility - there's a rag or piece of paper stuck in the air intake that gets lifted and blocks air flow at higher RPM, then falls off and lets air in when RPM drop.  RPM increase, air block, RPM decrease, aor open, etc....

 

It's probably a fuel supply issue though.

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Check your fuel pressure again. The FPR should hold the PSI at 36 above what's in the intake. At WOT the psi in the intake will be atmosphere which is where the gauge on the fuel rail is referenced to. So, at WOT your gauge should read 36. At idle it should read 36 - your vacuum reading in PSI, not inches HG.

 

If your vacuum is reading 20" HG (around 10psi) your fuel psi should read 26. From the video, it looks like your psi is too high to me which would definitely cause a rich condition. It is hard to tell exactly & you may be ok, but it looks like you are reading 32 psi around idle, and you have around 20"hg vacuum at the same time. If that's true you have 6psi too much pressure on the rail.

 

Lenny

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Another strange possibility along the same lines as NewZed's is the AAR. If the valve inside it has somehow became loose/broken and is bouncing around that would be just like you blipping the throttle open/closed. I've never heard of this happening before, but it would make your idle erratic as hell. You can easily test by just temporarily clamping the hose leading to it with a pair of pliers. If the jumpy idle goes away that would tell you something.

 

Len

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Well, good luck with it.  Engine RPM can be affected by three things - air supply, air/fuel ratio, and timing.  Timing is a possibility but if you had your vacuum advance connected to full-time vacuum I would have expected idle speed to increase and stay high.

 

Engine speed affects fuel pressure through the FPR vacuum hose, and timing advance through the advance diaphragm.  Maybe disconnect those things, then start the engine and see if fuel pressure varies, or behavior changes.

 

 

Here's an odd possibility - there's a rag or piece of paper stuck in the air intake that gets lifted and blocks air flow at higher RPM, then falls off and lets air in when RPM drop.  RPM increase, air block, RPM decrease, aor open, etc....

 

It's probably a fuel supply issue though.

 

I'll disconnect the FPR hose and advance diaphragm and see what changes occur. Thanks

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Check your fuel pressure again. The FPR should hold the PSI at 36 above what's in the intake. At WOT the psi in the intake will be atmosphere which is where the gauge on the fuel rail is referenced to. So, at WOT your gauge should read 36. At idle it should read 36 - your vacuum reading in PSI, not inches HG.

 

If your vacuum is reading 20" HG (around 10psi) your fuel psi should read 26. From the video, it looks like your psi is too high to me which would definitely cause a rich condition. It is hard to tell exactly & you may be ok, but it looks like you are reading 32 psi around idle, and you have around 20"hg vacuum at the same time. If that's true you have 6psi too much pressure on the rail.

 

Lenny

 

I'll have to compare the HG to fuel psi when I have a helping hand, this time I did not.  I'll get back with some data if disconnecting the FPR hose doesn't alter anything.

Edited by AdreView
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Another strange possibility along the same lines as NewZed's is the AAR. If the valve inside it has somehow became loose/broken and is bouncing around that would be just like you blipping the throttle open/closed. I've never heard of this happening before, but it would make your idle erratic as hell. You can easily test by just temporarily clamping the hose leading to it with a pair of pliers. If the jumpy idle goes away that would tell you something.

 

Len

 

Not so strange...upon pulling and cleaning the wiring harness connections and associated components the harness plug on the AAR came off with the harness.  This was a potential vacuum leak as it was no longer sealed.  I removed the plug with the bi-metal element attached, checked the AAR internal gate for proper operation (was not sticking or stuck) and reassembled the plug/element with some sealant.  Doing this actually increased the idle vacuum to where it is now from prior bouncing from 7-10.

Edited by AdreView
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Ahhh...the plot thickens. LOL 

 

You're saying the actual connector that's supposed to stay with the AAR came off, right? That's another failure I haven't seen nor heard of, but if the AAR had any leak you would get higher idle and leaner burn of course. I don't think it's the cause of the rich condition.

 

The rich condition is something else, again maybe the FPR. If you're engine is really as tight as indicated by your compression numbers and the valves aren't horribly mis-adjusted, your car will hold a pretty good vacuum at idle, 20" perhaps. Just judging by hearing your rpms on the video & watching that fuel PSI gauge, your fuel PSI is too high. I normally see around 26-28psi at idle, drop a little as you blip open the throttle and then climb to 36 when wide open of course..

 

Replace the small vacuum line from the FPR to the intake when you're checking it out next time, even if it looks ok. That little piece takes a fair amount of heat abuse and a small intermittent split might be causing a lot of your problems. Without that connection sealed and solid, your fuel pressure will definitely be too high at idle (which is what I think I see in the video).

 

Len

Edited by superlen
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Ahhh...the plot thickens. LOL 

 

You're saying the actual connector that's supposed to stay with the AAR came off, right? That's another failure I haven't seen nor heard of, but if the AAR had any leak you would get higher idle and leaner burn of course. I don't think it's the cause of the rich condition.

 

The rich condition is something else, again maybe the FPR. If you're engine is really as tight as indicated by your compression numbers and the valves aren't horribly mis-adjusted, your car will hold a pretty good vacuum at idle, 20" perhaps. Just judging by hearing your rpms on the video & watching that fuel PSI gauge, your fuel PSI is too high. I normally see around 26-28psi at idle, drop a little as you blip open the throttle and then climb to 36 when wide open of course..

 

Replace the small vacuum line from the FPR to the intake when you're checking it out next time, even if it looks ok. That little piece takes a fair amount of heat abuse and a small intermittent split might be causing a lot of your problems. Without that connection sealed and solid, your fuel pressure will definitely be too high at idle (which is what I think I see in the video).

 

Len

 

Yes, the connector and the bi-metal element which it's attached to came right out as one.

I'm going to check the seal on the AAR again, just for piece of mind.  I could even go so far as to pull the AAR off and run a new hose to bypass it all together if its actually damaged...but I don't think its the cause of running rich either.

 

I'll inspect the FPR hose and replace it.  So the FPR is non-adjustable, what options do I have for testing it?

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Did you check the PCV valve, it's under the intake....

 

Yes sir, replaced with new pcv valve, hose cleaned and inspected, reinstalled with new clamps on both ends.  Prior to this the pcv hose on the block end was loose and bleeding off spraying all over the A/C motor and pulley....quite a mess.

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Yes. The FPR is non adjustable. The only test is to compare the rail PSI to what it should be given the current manifold vac like your doing. Always there should be 36psi difference. If you have a vac pump like a mighty vac, you can attach it in place of the manifold and watch the rail pressure go up/down as you release/apply vacuum.

 

You would need to make sure the fuel pump is running during this test either by holding the AFM vane open (simulating airflow to the engine) or by jumper wire, or by pulling wire to starter solenoid & having someone hold the key in the "start" position.

 

BTW, if you just bypass the AAR with a hose you will always be in high idle mode. It's easier to just pinch the hose on either side with vice grips. That will take it completely out of circuit and you can test the rest of the system.

 

Also, I watched the video more closely and it looks like your getting around 30psi with 10" in the manifold. Those match so your FPR is probably ok. Other sources of rich condition are of course the AFM and/or the ECU. I'm doing a bunch of tests on AFMs currently. PM me if you have any questions.

 

Len

Edited by superlen
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