Hi all,
For the last 5 weeks, I've had problems with stalling at idle and slight hesitation at speed on my 97 Max SE (auto, 168k miles).
I have taken my car to three mechanics - the first one (Firestone) said my fuel pressure was bleeding and replaced the fuel pressure regulator. I still have the problem.
After taking my car to Firestone, I took the car to a Nissan-trained mechanic, who also happens to be a friend of mine. He spent two solid hours at my house diagnosing the problem. He double-checked the fuel pressure - at idle, it would stay steady at just over 30 psi, running higher when you open the throttle. He was able to reproduce the stalling, and noticed that whenever it would stall, the fuel pressure stayed steady at just over 30 psi, seeming to prove that fuel pressure wasn't the cause of the stall.
Other tidbits for the detectives out there :) :
- engine would never stall at speed, but only as I come to a stop, accelerate from a stop, or while stopped at a light. At speed, I might feel a lurch or two, as if the engine were losing power briefly, then catching itself. Engine stalls whether idling in Drive, Neutral, or Park.
- I seem to remember noticing this problem soon after filling-up at a Mobil gas station. I have since run through that tank of gas, and have now re-filled twice more.
- Whenever the engine would stall, it would usually restart right away, but sometimes I'd have to "gun" the throttle a bit to get it to stay running.
- Check Engine light is NOT lit, but the computer is giving a 0304 code, indicating trouble with the knock sensor. The 2nd mechanic doubted that this would be causing the stall as all the computer should do is retard the throttle and not kill the engine altogether. Does that make sense?
- A couple times, while test driving with the 2nd mechanic, when the engine started to hesitate in the process of stalling, we pushed the (automatic) transmission to Neutral, but the engine still sputtered and stalled. The mechanic seemed to think that this proved the transmission likely wasn't causing the stalling. Also, the fact that the stalls occur while in Park, Neutral, or Drive would seem to eliminate the A/T as the culprit.
- Shortly after noticing this problem, I had a tune-up done, so new NGK platinum spark plugs, new fuel filter, new air filter, and clean throttle body. Also put in a new PCV 4 weeks ago.
- Also just put in a brand new battery about 4 weeks ago.
- Last week, I took apart and cleaned the IACV (following great instructions from motorvate.ca). I even took apart the plastic valve and verified that the plunger moved smoothly in and out while its drive shaft was turned.
- Also last week, I adjusted the base idle up close to 1000 RPMs, thinking it just needed to be bumped up. Problem is still here.
- The Firestone place also said that my fuel pump was weak. My friend mechanic didn't think it could be the fuel pump as the fuel pressure remained strong even after the engine stalled. Would the above symptoms support a failing fuel pump? I have never replaced it in the 168k miles that I've owned the car (I'm the original owner.) Is there a diagnostic test? Is it easy to get to the fuel pump?
My friend mechanic concluded that there were no problems with the fuel delivery, and no electrical issues as the engined seemed to run perfectly except for the occasional stalls, and after two hours of diagnosing, the best he could come up with was that I probably got bad gas.
Based on that, I put in two bottles of HEET when I filled up two tanks ago. Problem is still here.
I was just wondering what the collective wisdom of the forum thinks.
- Based on the history above, does the diagnosis of bad gas hold up?
- Are there other things that should be checked? -
- Should I have the knock sensor replaced?
Thanks everyone!