Rich in limp mode

[Jin1976]

I was driving the car in limp mode for a while and notice that the car consume more fuel than it was in when the CEL is not on. Also notice that the car run smoother in limp mode than when the CEL was not there. Can somebody explain to me why it consume more fuel when I thought at 4,000RPM the fuel is somewhat cut off during limp mode. Btw the fuel pressure regulator needs replacing.:frown:

 

[Daedalus]

Common for cars to protect the engine when the ECU detects a problem by running rich. Reduces the risk of knocking and overheating. Running rich causes the engine to run smoother, but you've probably noticed it's more sluggish too. Sure there's a cutout due to the limp-mode, but it runs rich all the way until then. Pressure regulators rarely fail--what was the fuel pressure at idle?

 

[Jin1976]

Honestly I have not check yet. but since all the others have been check except for the input (speed sensors, thermostat and fuel pressure regulator) my bet was the one I mention.

Common for cars to protect the engine when the ECU detects a problem by running rich. Reduces the risk of knocking and overheating. Running rich causes the engine to run smoother, but you've probably noticed it's more sluggish too. Sure there's a cutout due to the limp-mode, but it runs rich all the way until then. Pressure regulators rarely fail--what was the fuel pressure at idle?

 

[drew]

Trying to say this nicely: You are probably on the wrong track. No NSX has this many problems, my bet is that you are working with very limited knowledge of how things work. STOP IT. Get your knowledge first, get some test equipment and start a log.

You NEED to READ and UNDERSTAND how engine management works. You need to curl up with the shop manual at bed time and knock off a few pages a night. I have an inside, outside and desk copy of my NSX manual: it is THAT important when diagnosing problems like this.

Once you know what to look for: start looking! Measure your sensor values as you drive around (fuel pressure, coolant temp, AFR, at a minimum). When stopped, when running etc... You can use a www.innovatemotorsports.com set up with your laptop so you can just drive around. (In fact, they have nice videos on their site on how fuel management works: watch them!)

The other problem is that you and your mechanic seemed to have messed with some critical adjustments that may not be fixable outside the factory. Personally, I would purchase for a whole new intake and throttle body or borrow one from a friend. Making random adjustments is just plain suicide in this arena.

Limp mode just pours fuel down into the engine as a safety precaution. Why? Well, with more fuel the engine runs cooler and prevents detonation. Chances are that the engine is confused and can't figure out what is wrong---probably an unhappy sensor somewhere.

However, you need to get this fixed because you can ruin your cats and O2 sensors running too rich.

To recap:
1. Learn how things work
2. Get test equipment
3. Measure and Log test results.
4. Apply knowledge and fix your car
5. There are NO SHORTCUTS

Blind Luck is not a strategy.

Unless your TEST RESULTS show that the regulator is bad: I doubt it too. Guessing is not a test result.

Drew

 

[Jin1976]

Thanks for the advice. I will read again the test procedure of what are the things to be checked. My friend is just trying to undo what the so-called expert mechanic have done with the intake manifold. My friend was a Honda mechanic before he worked in Saudi Arabia on European cars (Ferrari & Lambo) then came to Brunei. The main and only Honda dealership knows much about him. The place where we do the checking does not have computer gadgets to use to check so most of them is just by visual inspection and using some small meters as used by instruction in the repair manual. Maybe I'll try to find some good shop that can diagnose the problem using their computers. Some big shops here just say they know when infact they do actually worsening the condition of the car.

The other problem is that you and your mechanic seemed to have messed with some critical adjustments that may not be fixable outside the factory. Personally, I would purchase for a whole new intake and throttle body or borrow one from a friend. Making random adjustments is just plain suicide in this arena.

 

[drew]

You do NOT need elaborate computer testing rigs and harnesses. A few manual gauges taped to the rear glass while you are driving round is good enough.

It is system knowledge and logging that key right now; and you can easily do that yourself--in fact, I highly recommend it

If you have USD$1200 you can buy an elaborate test harness with computer outputs. This system has to be learned; further compounding your pain. (If it is not painful: you are not learning).

This engine management stuff is not that difficult with stock ECU's. There are not very many inputs/sensors that you have to worry about. But the computer learns and makes non-obvious control decisions.

What has made YOUR car difficult is that we have no idea what baseline you are operating from. Some critical "factory only" adjustments may have been botched, other adjustments were made blindly and I'm also guessing that original problem that started this whole thing still remains.

"Learn, understand, record and modify"

Drew

 

[Jin1976]

I guess I'll bring it to one very reputable shop with computers to check everything. It already gave me a lot of headache on top of my migraine.

This system has to be learned; further compounding your pain. (If it is not painful: you are not learning).

Drew