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I have the same 94 V6 SE 4x4 truck that Crystal has, and a very similar problem that just developed this past week: Severe lugging/lurching in lower gears. It is apparent in 3rd and 4th gears as well, but not as noticeable as there is proportionately less torque transfer. The problem seems to happen only after the engine is warm - 5km or so from a cold start (that's about 3 miles - sorry, I'm Canadian). I notice it when the truck is idling too - it runs fine for 20 seconds or so, then almost stalls and revs back to normal idling speed.

Fuel delivery checked out fine. This feels electrical to me. I can't find any hints for how to diagnose the ignition coil in the service manual. Suggestions would be much appreciated - I am the second owner of this truck (we are both Engineers and good friends, and I want to keep it in the family so to speak). It has only 160,000 miles (not km; it was imported from California and modified for Canada).and has been a real workhorse.

Crystal, if you are still there, I am wondering if you were ever able to resolve this problem? On a side note, I too smell fuel when starting the vehicle on cold winter mornings. I know what causes that - the seals on the fuel injectors stiffen with age and shrink with temperature, so a bit of fuel vapour leaks out. Once the engine is warm, the seals expand and do their job properly again. I heard this diagnosis first from Click and Clack on NPR's CarTalk about ten years ago, and that was it for me. They said this is not a serious or safety issue, and you can safely ignore it if you choose.

Thanks - Trevor
 

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Thanks so much for your prompt response, smj
!
The truck is at my Nissan dealership right now, but they lost their service manual and OBD tools for this model year/engine, hence why I am researching and soliciting opinions. Their first thought was fuel delivery, but it tested fine (at my cost). My first thought was distributor/ignition coil intermittent - so it is good to receive your second opinion. I will run the diagnostics and see what sorts of error codes appear. I downloaded the service manual and found the ignition coil tests you mentioned - thanks for the specifics. Here in Canada it can be hard to source old parts. Do you have any idea what I should expect to pay for a new ignition coil assembly? I will follow your recommendation for a genuine Nissan part - thanks for that. Regards -Trevor
 

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Thanks again smj. The diagnostics look straight forward to me. Can you tell me where I can find the replacement part numbers in the service manual? I am wondering whether the distributor, optical sensor, shaft bearings, etc. that you mentioned are sold individually or as an assembly. I will ask the dealership about ordering Nissan re-manufactured parts, but I might end up having to source these parts myself. By the way, if you are looking for an easy place to download the entire service manual as a compressed file, try this: Nissan Hardbody D21 Truck Service Repair Manuals. Thanks - Trevor
 

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Hi again smj - thanks again for your advice. I have the truck at home again and will look at the ECM tomorrow. Is the ECM under the passenger seat or driver seat? Dealership says driver side, all the video tutorials show passenger side. Maybe it's different as I have a 4x4 SE V6. I can feel boxes under both.

According to the dealership, in addition to the lurching fix, I need the following, in order of importance: Rear Propeller Shaft centre bearing support assembly; both front lower ball joints, both front calipers, right front wheel bearings (possibly). Yikes. They are quoting $3200 to do all that work, plus the lurching fix (which I will diagnose via ECM tomorrow). The truck has 170k gentle miles on it, west coast only (no salt, no off-road, mild winters). Dealership recommends I abandon it; I only use it for ~4k miles/year (minor house renovation work) so I am loathe to invest thousands more into a monster truck that I don't know, need, nor want. I love the 4x4 SE V6 I have. Do you think it is worth salvaging?

I can afford the work - but I don't want to sink money into a hole if I can avoid it. Parts availability looks like a serious issue. My goal would be to squeeze another ten years and 50,000 city miles out of it. I replaced timing belt and clutch plates at 160k. Ideally, it would retire the same week I do... If I were to buy new, I would much prefer BEV (I own a Leaf already) but no viable options are yet available. Thanks again - Trevor
 

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Hi again smj - Thanks again for your advice - I ran the diagnostics and here is what I have found so far:

  • Switched accessories on, (i.e. left engine off)
  • Error code 34 (Knock Sensor) was stored in ECM memory
  • Started engine; Mode 3 Code 34 still active (and symptom present while idling)
  • Entered Mode 4 to clear memory (I wanted to see if any other codes came up)
  • Entered Mode 3 again and observed Code 55 (no fault detected) which seemed odd
  • Shut engine off, re-started, let run (rough) for two minutes
  • Entered Mode 3 and observed Code 34 again.
  • Shut engine off.

Continuity confirmed between the KS connector pin E through the harness to the ECM connector pin 27. From the KS connector pin E on the engine side of the connector to ground (battery negative post) there is an open circuit. The manual page EF&EC-137 indicates continuity should be present here.

The harness seems fine. Suspect KS is faulty (or at least, not referenced to ground). I see no obvious damage to the wiring harness from the KS connector into the engine.

I can't find any further hints in the manual from here. Page EF&EC 15 indicates that the KS sensor is mounted directly in the block, under the intake manifold. Somewhere I read that removal/replacement of that is 4-6 hours of work.

I would not have though the KS would cause this problem; rather, I think it is measuring a symptom of the problem (engine knock, likely due to improper or untimely ignition). That said, I also read the the ECM retards the ignition signal if the KS signal is TRUE, and perhaps if the KS is dead then the ignition is too delayed.

Have you seen this situation before? Can you suggest any other diagnostics I should run before replacing the KS (assuming I can find one...)?

Many thanks - Trevor
 

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Hi again smj - I forgot to mention the ignition coil impedance - I measured 1.1 ohms between pins A-B on the LV connector side and 12.44 kohms between pin A and the HV output pin C. The manual calls for "approximately 10 kohms" from A to C; I'm 25% above that, which seems high to me. Inductors in my experience fail open; their resistance doesn't change over time. Perhaps it's different with ignition coils. Any thoughts here? The good news is that both the ignition coil and the knock sensor appear to be available from nissanpartsdeal.com. Thanks again - Trevor
 

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That is an interesting idea - I would be able to install a new knock sensor without doing anything to the intake manifold, and while doing so I would splice out any breakage in the KS harness too (since I am reading open circuit from the main harness connector to the KS). FYI smj - I started a new thread on this problem because I hijacked Crystal's old thread here and wandered off topic a bit. The new thread is here: 1994 VG30E 4x4 SE Truck - Severe Lurching/Lugging at...
I'll copy your notes over, and thanks again for your time and suggestions.
 
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