Rebuilt engine idle problems, running rich

[MrChefur]

Howdy everyone,

I've got a rebuilt L28 I just got running in my 78 280z. I'm having issues with my idle. It sits at about 1100rpm and runs very rich, plugs had black soot all over the tips after about 15 minutes of idling. It also runs very poorly at lower RPMs. Here's what I've done so far:

• Vacuum check by taking off oil cap with engine running. Engine died, which I've read means I have decent vacuum?
• Throttle position sensor: I've got two of them, one on the car and one spare. Adjusting them either way increases and decreases idle, but disconnecting the cable makes no difference. Swapping one for the other makes no difference, despite one being in far better visual condition than the other.
• Cold start valve: disconnecting makes no difference
• AFM: disconnecting makes RPMs bounce dramatically
• EFI Bible: I tested resistance, continuity, volts, etc for every spec the EFI bible gives and all checked out within specs.
• Thermotime switch and water temp sensor: I swapped the cables between the two with no effect which worries me. They both meet the resistance specs in the EFI bible though, what gives?

Thanks everybody. Let me know if there's something I've missed.

[siteunseen]

Is the vacuum hose hooked up and in good shape to the fuel pressure regulator?  All the air hoses are routed the right way?  Sounds to me like it's not getting enough air.  The throttle blade may be inoperable?  Have you taken the black cover off the AFM and "fingered" the vane with the weight on the other end?

http://atlanticz.ca/zclub/techtips/EFI&fuel.htm  Thanks @240260280 for this information

 

 

[rcb280z]

How did the car run before the engine rebuild? Why did you have it rebuilt? Some more details like these may help you and others on this site trouble shoot the problem.

[MrChefur]

1 hour ago, siteunseen said:

Is the vacuum hose hooked up and in good shape to the fuel pressure regulator?  All the air hoses are routed the right way?  Sounds to me like it's not getting enough air.  The throttle blade may be inoperable?  Have you taken the black cover off the AFM and "fingered" the vane with the weight on the other end?

I'll try these and get back to you today. Thanks

 

1 hour ago, rcb280z said:

How did the car run before the engine rebuild? Why did you have it rebuilt? Some more details like these may help you and others on this site trouble shoot the problem.

I bought the rebuilt engine off of a family friend who was going to use it to restore his Z, but decided to do a swap instead. The engine out of my car has a spun main bearing and it worked out to be cheaper to buy his already-rebuilt engine than it was to have mine done. He had it rebuilt by a shop (not himself) and it was very well done from what I and my father can tell.  I don't know very much about rebuilding, so if you need more details I'd be happy to help however I can.

[Dave WM]

if its running rich, 1st thing is to get an accurate fuel pressure reading. Next is to clean all electrical conditions, including grounds.

when you disconnected the CSV, did you literally remove the fuel line to it? or just disconnect the electrical connection.

Did you check the temp sensor resistance value to a temp chart and check it at the ECU 36pin connector?

Listen to all the injectors with a stethoscope to see if they all make the same tapping sound while running.

have you checked the air filter?

have you checked all the vacuum lines/PCV hose on the crank case/AFM boot. Just regular stuff that should be done when ever going over the EFI for correct air metering.

 

[MrChefur]

20 minutes ago, Dave WM said:

if its running rich, 1st thing is to get an accurate fuel pressure reading. Next is to clean all electrical conditions, including grounds.

when you disconnected the CSV, did you literally remove the fuel line to it? or just disconnect the electrical connection.

Did you check the temp sensor resistance value to a temp chart and check it at the ECU 36pin connector?

Listen to all the injectors with a stethoscope to see if they all make the same tapping sound while running.

have you checked the air filter?

have you checked all the vacuum lines/PCV hose on the crank case/AFM boot. Just regular stuff that should be done when ever going over the EFI for correct air metering.

Cold start valve: I couldn't figure out how to plug the fuel line to it, so I swapped it with the cold start valve from my other intake as well as disconnecting the connector. I suppose they both could be bad, however. 

Temp sensor: Yes, I checked it with the temp chart at the ECU connector and it checked out fine.

Injectors: I will do that today. I tried yesterday with a rusty old pipe but it was too big to fit haha. Probably shouldn't try troubleshooting at 10pm anyways

Air filter: brand new, put it in right before the first start up. Stock air filter box and rubber boots as well.

Vac lines/PCV: I checked all of them and they look to have been replaced shortly before I got the car, with the exception of the PCV -> crankcase hose. It's quite old but doesn't seem to leak. I can't seem to find any hoses that fit it either, seeing as one end is larger than the other. I'll go through all the hoses again today to make sure.

 

I took a video of it running today, hopefully this will help a little:

 

Edited August 5, 2017 by MrChefur

[MrChefur]

I just pulled the spark plugs again on a whim, and something weird is happening. With the spark plug closest to the front of the car being number 1 and the one closest to the firewall being number 6, here's what I found:

1. Black with soot. Most of it rubs off by hand but some is stuck.
2. Same as 1
3. Same as 1
4. Somewhere in between clean and sooty
5. Basically clean? smells like gas. Had minor black soot but nowhere near as much as 1
6. Same as 1

I also listened to the injectors with a steel tube and all of them are clicking at the same rate. I'll try the other troubleshooting and come back, I just wanted to type this while it was fresh in my mind.

Edited August 5, 2017 by MrChefur
edited to correct order of numbering

[Dave WM]

what's going on with the TPS sensor? should not be able to move it like that.

Battery sound weak.

no reason to do anything else until you get the fuel pressure checked out. Also sounds like a miss fire disconnect "basically clean" spark plug (connect the cable to a spare plug and lay it on top of the valve cover so you can see the spark is working). Does the engine run any different with that plug disconnected from the engine?

BTW to avoid confusion 1# is the closest to the front of the engine, #6 is the closest to the firewall.

At some point you are going to want to do a compression check, see how well balanced everything  is. should be around 140-155 psi per cylinder, all about the same.

 

Edited August 5, 2017 by Dave WM

[MrChefur]

1 minute ago, Dave WM said:

what's going on with the TPS sensor? should not be able to move it like that.

Battery sound weak.

no reason to do anything else until you get the fuel pressure checked out. Also sounds like a miss fire disconnect "basically clean" spark plug (connect the cable to a spare plug and lay it on top of the valve cover so you can see the spark is working). Does the engine run any different with that plug disconnected from the engine?

BTW to avoid confusion 1# is the closest to the front of the engine, #6 is the closest to the firewall.

Throttle position sensor has two screws on either side and looks like it was made to be adjusted, even has little hash marks. Not sure what for. 

Battery is pretty old, haha. It's charging well when running though.

I unplugged injectors one by one while it was running and all of them caused the engine to stumble until it stalled.

I also messed with the AFM and rotating it caused the following results:

• All the way shut against the stop: engine stalls (no suprise)
• Let it sit where it wants to: runs like in the video
• 10 degrees further: idle RPM goes up from 950 to about 1200
• No real change until about 20 degrees past that, where the engine begins to stumble
• 15 degrees past that: stalls

I pulled the wire from the "clean" plug and started the engine, it ran the same as with the cable plugged in. I did as you said with the spark, and it appears to be getting good spark which thoroughly confuses me. I also swapped the spark plug wire with another and it didn't change either. Does this mean it's the injector?

I also checked compression, here's how it read (in correct order, from front to back this time )

1. 148
2. 145
3. 147
4. 150
5. 145
6. 145

I'll go pick up a fuel pressure gauge and report back.

[Dave WM]

something odd with that one, if you pull the plug wire and is does not effect anything then something is up. Does not follow that you disconnected the fuel injector and it does effect the idle. You are disabling the cylinder either way, should get the same result.

I suggest you try that again, disable the injector and see what effect it has. then the Plug. If that one is dead and you are getting a spark, you should pull the injector out and see if its actually passing fuel. The fact that it was wet with gas makes it seem like a spark issue. Do all that over and confirm the results.

[MrChefur]

Alright, here's a video of the issue:

Video ends because I'm an idiot and shocked myself with the wire . Also, I know the connectors are old. I've got new ones on the way.

EDIT: because I didn't explicitly state it, the engine continued running exactly the same after I pulled the wire and shocked myself.

Edited August 5, 2017 by MrChefur

[Dave WM]

hmmm, sounded like it started to slow down but you are there so will go with what you say. Anyway does not really make any since if you disable a cylinder is should slow down either way.

But back to the issue, check the fuel pressure, look for vacuum leaks, set the TPS to the correct setting (use the FSM). Make sure all electrical is correct, make sure the Temp sensor is hooked up right, put in some new plugs run it for a bit then read the plugs again.

fuel pressure should be 36psi with the pump on but the car engine NOT running. with it running should drop down to around 30psi.

To disable the CSV all you need to do is unplug the fuel line and clamp it off. The TSP contributes to the fuel mix at idle and full throttle, should be set correctly. The temp sensor is the one that effect warmup mix the most. Hopefully no one as monkeyed around with the AFM. I think its a fuel pressure thing, need to make sure the FPR is working right and lowering the pressure after the engine starts and generate a vacuum in the intake manifold.