Low RPMs bucking

[MuRCieLaGo]

Update:

Removed fuel pumps assembly and visually inspected it. Everything seems to be fine.

Went under the car to double-check the fuel filter (without success), I found something interesting instead.

https://www.youtube.com/watch?v=fHqLdS43baU

One of the wire in the o2 sensor connector is loose, as you can see in the video. I'm going to fix it tomorrow morning (will replace the connector). It is the passenger side o2 sensor, it probably explains why I got code 64 showing up (and why I had the code only since I replaced the fuel filter. The connector is fixed to the fuel line... I probably broke it while working on the fuel filter).

But I'm still scared about the knocking noise.

Started the car this morning to park it in and out of the garage and I didn't hear the noise, but it is still a concern.

[geezer]

Monitoring your situation & progress/ frustration! I'm closer than T.O. being in Ottawa area so if I can help in anyway.

[MuRCieLaGo]

Originally Posted by geezer

Monitoring your situation & progress/ frustration! I'm closer than T.O. being in Ottawa area so if I can help in anyway.

Good to know thanks for your support! I'm still 450 miles from Ottawa...

[Paul Workman]

I'm back. See additional info on my earlier post.

[Bruce]

I just logged into this forum. After reading the site for the last year Ive just joined.

Ok, the knocking sound you have is the clutch unit on the AC compressor. Not a biggie, its just rattling around as you will see if you get closer and have a look. Thats why the sound will come and go. I had the same thing on mine, and I just replaced the clutch unit and its sweet as now.

[MuRCieLaGo]

Originally Posted by Paul Workman

[...]Rough idle and or a knocking sound (dual mass FW**), low rpm, stalling, running OK when cold, but rough when it warms up, running OK with rpm and/or moderate to heavy throttle (esp. WOT) are classic fuel delivery issues at CLOSED LOOP ONLY.

**If the knocking sound goes away when you depress the clutch pedal, it is probably the result of rough idle pulses which usually causes a knocking sound from the dual mass flywheel. This is but one of the tell-tale signs of a bad injector or an O2 sensor issue.

Running strong at (OPEN LOOP) tends to eliminate fuel delivery pretty much in your case. However, just for the record (FYI) a dynamic fuel test will expose weak pumps or plugged in-line filter (you DO know there is an in-line filter (located just behind the front passenger wheel housing), yes?



In closed loop conditions, and fully warmed up, the dynamic pressure will be around 42-45 psi. in open loop conditions the combined fuel pressure will be 52-55 psi.

Injectors: My injectors had just been replaced when I bought my 90 Z. At issue was they were replaced with NOS, and they too went bad due to alcohol exposure! SO! Unless you've checked resistance when the motor is fully warmed up, you can't be sure they are good. Typically the shellac-insulaiton on coils fails, it goes undetected until the coil is heated. There are a couple ways to take the resistance readings. How and under what teperature conditions did you test yours, may I ask?

Throttle Position Switch: Sometimes the TPS wiper is dirty or has failed. This too is FYI, and not related to closed loop per se'. By disconnecting the electrical plug you can operate the TPS through its enter throttle range while watching the (analog) resistance indicator on the VOM, looking for a smooth change in resistance through the entire range.

With the connector reassembled and the ignition switch to ON, motor OFF, the TB wiper should be set to 5.5 VDC.

O2 sensors:

The O2 sensor operation (including 'cross counts') can easily be monitored with a dynamic scan (most auto parts stores have that capability). And, also, the sensor can be removed and tested with a VOM and a propane torch.

https://axleaddict.com/auto-repair/H...-Oxygen-Sensor

A lazy (low # of cross-counts) or non-responding O2 sensor, especially an intermittently failing one can result in a number of closed loop symptoms (but not exclusive of closed loop operation either!) - especially idle irregularities and rough running, fouled plugs (on one bake only...is important to note) are some of the more common issues.

Not because of your symptoms in particular, but more of an FYI, you asked about checking the coils.

Well, the acid test for ignition is proper operation at WOT when the motor is fully warmed up! Furthermore, a pin-hole can develop in a wiring insulation that cannot be detected with a standard VOM: a MEGGAR or dedicated test equipment is required, which is uncommon except in the better repair shops.

The LT5 uses a "waste spark" design. Each coil fires two plugs at the same time.



That said, the resistance can be measured across the spark terminals and compared with the readings across all 4 coils. (But, again, not all coils e.g., AC/Delco, MDS, Excel, etc. read the same, specifically, and may vary from type to type!) Plug wires resistance values vary too, depending on the make/type. However, the resistance should be proportional to their length; i.e., a wire twice as long as another should have close to twice as much resistance as the shorter one.


Well... w/o more specific info, this could get very superfluous (if not already!). So, I'll stop till I hear more specifics from you first.

Knocking sound doesn't go away when I depress the clutch pedal.

I changed the fuel filter (which is behind the front passenger wheel housing).

I'll try to find a fuel pressure gauge extension to run a dynamic test. Or, even easier would be to buy 2 new pumps at RockAuto...

I can't tell you at which temperature I tested the resistance of the injectors, I don't remember. I add this to my todo list (after changing the o2 sensor connector). I tested the resistance using this diagram:



For the TPS: can't I unplug it and hook a multimeter in the TPS plug to see the voltage fluctuation?

What's a VOM?

For the o2 sensor test, to be honest if I have to remove them I'll simply change them.

Coil packs: they'll be in my todo list as well as the spark plug wires, but pretty low on the list at the moment.

"Waste spark design", I think they are just like a 3.4 2000 Grand Am. And I'm pretty sure they even fit in there...

Originally Posted by Bruce

I just logged into this forum. After reading the site for the last year Ive just joined.

Ok, the knocking sound you have is the clutch unit on the AC compressor. Not a biggie, its just rattling around as you will see if you get closer and have a look. Thats why the sound will come and go. I had the same thing on mine, and I just replaced the clutch unit and its sweet as now.

Happy to read this. However, I'm not sure it's the problem. There is no change when I put A/C ON or OFF. I appreciate that you post on this thread as your first post!

Knocking sound is irregular, so I hope I can assume it is more a rattle than a knocking sound.

Actual todo list:

1. Fix o2 sensor connector.
2. Change spark plugs (I'm receiving my BKR7EIX11 plugs tomorrow, it can't hurt). I'll ask a mechanic nearby what he thinks of my old plugs.
3. Test the resistance on the fuel injectors (car hot).
4. Dynamic test fuel pressure.

[Dynomite]

Originally Posted by MuRCieLaGo

What's a VOM?

VOM is a Volt Ohm Meter among other uses of the abbreviation VOM

One of the first tests I always do is a Compression Test on Zs which does not have much to do with your issue but just saying.

A compression test says a lot about the valves, Cylinders, and general wear of the engine. A compression test also says a lot about the uniformity of the wear among cylinders and uniform compression assures uniform work done by each cylinder.

Your first post suggests "Severe Buckings".
You have since suggested Knock.

You suggested the LT5 has behaved like this for 3,000 miles.
Also you suggested total power loss for a revolution or more but immediately returns to normal.

I have some ideas but what I do on ALL LT5s/ZR-1s is do my typical Top End after the Compression Test (The Compression Test is conducted to make sure I do not have Bottom End Issues). Once my Top End Restorations are complete the LT5s run perfectly with NO Codes for a very long time.

Part of that Top End of the LT5 includes the INFL REST restoration (the Air Bag Sensors re-grounded each side) including the Internal Wire each side. And part of that Restoration includes complete Brake Restoration and/or Installation of C5 Z06 Calipers and Rotors. Some more also but you get the idea

Oh....and my favorite Modification to ALL LT5s (Block TB Coolant at the Injector Housing).

[MuRCieLaGo]

Originally Posted by Dynomite

VOM is a Volt Ohm Meter among other uses of the abbreviation VOM

One of the first tests I always do is a Compression Test on Zs which does not have much to do with your issue but just saying.

A compression test says a lot about the valves, Cylinders, and general wear of the engine. A compression test also says a lot about the uniformity of the wear among cylinders and uniform compression assures uniform work done by each cylinder.

Your first post suggests "Severe Buckings".
You have since suggested Knock.

You suggested the LT5 has behaved like this for 3,000 miles.
Also you suggested total power loss for a revolution or more but immediately returns to normal.

I have some ideas but what I do on ALL LT5s/ZR-1s is do my typical Top End after the Compression Test (The Compression Test is conducted to make sure I do not have Bottom End Issues). Once my Top End Restorations are complete the LT5s run perfectly with NO Codes for a very long time.

Part of that Top End of the LT5 includes the INFL REST restoration (the Air Bag Sensors re-grounded each side) including the Internal Wire each side. And part of that Restoration includes complete Brake Restoration and/or Installation of C5 Z06 Calipers and Rotors. Some more also but you get the idea

Oh....and my favorite Modification to ALL LT5s (Block TB Coolant at the Injector Housing).

Thanks for the definition of the VOM (quite simple)!

I always hated doing a compression test. It's like inspecting your girlfriend while she's asleep. Not sure I want to know the numbers. But I'll do it soon...

I've seen your (more than complete) threads. I like modding my cars, but I want to fix the initial problems before, or the car becomes garbage pretty quickly.

[secondchance]

These are from 94 manual but hopefully it would help.

[MuRCieLaGo]

secondchance I just looked at it and it's pretty much the same for a 1991. Thanks for the reference...

Updated todo list:

1. Finally, I do not need to fix my o2 sensor connector. I went to the scrapyard to find the connector on another vehicle and they all had the same problem. Local electric shop told me it's normal, there's no problem there.
2. Changed spark plugs.


To do:
3. Test the resistance on the fuel injectors (car hot).
4. Dynamic test fuel pressure.


Here's a picture of the plugs. Driver's side to the left, passenger's side to the right. All the plugs from the right side (passenger side) are pitch black, it's a bit better on the left side (driver side).

Why the code says that I'm running lean on the right bank? Pitch black means too much fuel, no?