Starting a new thread on this topic as it has deviated somewhat from where it was initially posted.
1994 VG30E King Cab 4x4 SE V6 truck, VIN 1N6HD16YXRC402885.
This relates to severe lurching/lugging, particularly at low RPM and in lower gears, Problem is evident while idling (occasional drops in RPM and audible ticking sounds from engine what that happens). Problem is apparent when engine is cold, and appears to worsen as engine warms up. I took the truck to my local Nissan dealership. They confirmed fuel pressure is fine at engine intake. They did not have diagnostic tools for a vehicle this old, so I brought the truck home and diagnosed the following:
ECM reports Knock Sensor error code, Mode 3 Code 34. No other codes reported.
I tried the "dollar bill test" mentioned in another thread on this forum. The idea is to place a thin piece of paper at the tailpiece outlet to see if the outlet pressure is strictly positive or alternating positive/negative. I observed my bill being sucked flat to the tailpipe every time the hesitation/lugging symptom manifests – i.e. there is a sharp vacuum pull in the tailpipe when RPMs drop.
I looked for leaks in the air intake duct and Mass Airflow Sensor connections - all look/feel good and solid.
I confirmed continuity through the main wiring harness between the Knock Sensor connector pin E back to the ECM pin 27.
I observed open circuit when measuring through the KS harness from the connector pin E to the Knock Sensor. The manual indicates this should be short to ground - ergo Code 34. The KS wiring harness and connector terminals appear to be in good condition, well-wrapped, as far as I can see towards the back of the block. The KS is well-obscured by the intake manifold so I can't see the entire harness. The open-circuit appears to be a fault in the KS harness or the KS itself, I can’t tell which without cutting the harness open and knowing how to diagnose the sensor. I am not convinced this is the root cause of the problem, so I kept looking.
I loosened/tightened the grounding straps nearest the knock sensor connector to ensure good bonding. One screw was quite corroded, but able to take torque without failing. I measured continuity across the bond - seems OK.
I checked the impedance of the ignition coil. It seems alright - 1.1 ohms primary (pins A-B on LV side), 12.44 kohms secondary (pin A to HV output). The manual indicates the secondary should be "approximately 10k ohms”; I am reading 25% higher than that, but clearly there is a spark. HV wires are all NGK and all less than two years old. Distributor looks clean, but I did not pull out the whole distributor assembly to confirm that.
I confirmed the Power Transistor diode forward voltages are correct.
Thoughts:
Advice requested from the experts:
In addition to the occasional hesitation/lugging, I hear a continuous "gurgling" sound from the engine that seems loudest between the front of the block and the radiator. It is the sort of sound a stone might make when rolling around in the bottom of a plastic pail. Water pump perhaps? The vehicle was just given the full L/O/F service routine at a Nissan dealership, so I would assume everything was lubricated that should have been, and no mention of this noise was mentioned to me. Any thoughts on this sound?
1994 VG30E King Cab 4x4 SE V6 truck, VIN 1N6HD16YXRC402885.
This relates to severe lurching/lugging, particularly at low RPM and in lower gears, Problem is evident while idling (occasional drops in RPM and audible ticking sounds from engine what that happens). Problem is apparent when engine is cold, and appears to worsen as engine warms up. I took the truck to my local Nissan dealership. They confirmed fuel pressure is fine at engine intake. They did not have diagnostic tools for a vehicle this old, so I brought the truck home and diagnosed the following:
ECM reports Knock Sensor error code, Mode 3 Code 34. No other codes reported.
I tried the "dollar bill test" mentioned in another thread on this forum. The idea is to place a thin piece of paper at the tailpiece outlet to see if the outlet pressure is strictly positive or alternating positive/negative. I observed my bill being sucked flat to the tailpipe every time the hesitation/lugging symptom manifests – i.e. there is a sharp vacuum pull in the tailpipe when RPMs drop.
I looked for leaks in the air intake duct and Mass Airflow Sensor connections - all look/feel good and solid.
I confirmed continuity through the main wiring harness between the Knock Sensor connector pin E back to the ECM pin 27.
I observed open circuit when measuring through the KS harness from the connector pin E to the Knock Sensor. The manual indicates this should be short to ground - ergo Code 34. The KS wiring harness and connector terminals appear to be in good condition, well-wrapped, as far as I can see towards the back of the block. The KS is well-obscured by the intake manifold so I can't see the entire harness. The open-circuit appears to be a fault in the KS harness or the KS itself, I can’t tell which without cutting the harness open and knowing how to diagnose the sensor. I am not convinced this is the root cause of the problem, so I kept looking.
I loosened/tightened the grounding straps nearest the knock sensor connector to ensure good bonding. One screw was quite corroded, but able to take torque without failing. I measured continuity across the bond - seems OK.
I checked the impedance of the ignition coil. It seems alright - 1.1 ohms primary (pins A-B on LV side), 12.44 kohms secondary (pin A to HV output). The manual indicates the secondary should be "approximately 10k ohms”; I am reading 25% higher than that, but clearly there is a spark. HV wires are all NGK and all less than two years old. Distributor looks clean, but I did not pull out the whole distributor assembly to confirm that.
I confirmed the Power Transistor diode forward voltages are correct.
Thoughts:
- KS wiring harness might have a break in it; relatively easy to check/repair for the accessible portion of the harness.
- KS itself could have failed, but I don't know what its typical failure modes are (open? short? intermediate impedance?) and can't find conclusive information online regarding what to look for in KS failure diagnoses.
- I am not convinced that the KS fault is the root cause of the problem; it could be reporting a symptom of the problem. I don't see any other error codes however.
- I am thinking of replacing the KS as it has 170k miles and 27 years on it. That might not solve the problem, but it would rule out the KS as the root cause.
- I doubt this is relevant, but a few days before this fault showed up I used high-octane fuel for the first time in a year. Coincidence, or could there be causation?
Advice requested from the experts:
- Would a leak in the intake manifold cause the lurching/lugging problem?
- If there were a leak in the intake manifold, would I expect any other error code other than the knock sensor to be reported?
- Might the use of high-octane fuel be a factor?
- Could this be a sticking valve?
- If I were to remove the intake manifold and replace the knock sensor, is there any other preventative maintenance work I should do along the way?
In addition to the occasional hesitation/lugging, I hear a continuous "gurgling" sound from the engine that seems loudest between the front of the block and the radiator. It is the sort of sound a stone might make when rolling around in the bottom of a plastic pail. Water pump perhaps? The vehicle was just given the full L/O/F service routine at a Nissan dealership, so I would assume everything was lubricated that should have been, and no mention of this noise was mentioned to me. Any thoughts on this sound?