Misfire only when car stopped and then started

[vandale]

Hi everyone.

I have a 92 NA1 Manual NSX. Current mods are no AC, no TCS, no ABS, no airbag, K&N panel filter, exhaust, no cats.

Issue I have is that when I start from cold it runs great for as long as the journey takes. Revs to 8000 rpm, no hestitation, no misfire etc.

Once I stop the car, ie to get gas or pickup some milk then hop back in a start the car it idles fine but the second I try to accelerate it bogs and sounds like it missing, no backfire though, it lack in power and wont rev very high and to get high it takes ages. If I cruise in first gear and slowly accelerate it then suddenly comes right and wont fail until I stop and turn off again. If I leave it for an hour and start it then it works fine.

I have changed the following:
fuel filter
plugs
coils
igniter module (2 plugs and sits on top of the intake manifold)
ECU incl with and without a dali chip

Have checked timing and cambelt / cam timing all good. Head gasket all good also as checked with the radiator pump thingy that turns a different colour and compression was all good and no oil in water and no water in oil etc.

I have a spare motor that has only done 17000 genuine kms. I am about to try the throttle position sensors. Does the NSX have a air flow meter?

Also worth noting is that I didn't remove the TCS, ABS and airbag so I am wondering if it is related? What should I check for in relation to this, ie apart from unplugging the air bag and tcs boxes, what else needs to be done, anything needs to be bridged or shorted etc?

Thanks heaps. Am keen to get this sorted as its such a downer knowing each time I drive it does this.

Thanks

 

[ftuhy]

This is a totally wild guess, but could it be vapor lock in the fuel lines? Is a fuel line too close to one of the headers with no heat shielding? If you take a long drive, then turn the car off for, lets say 6 hours, to totally cool down - does it do it then?

 

[vandale]

This is a totally wild guess, but could it be vapor lock in the fuel lines? Is a fuel line too close to one of the headers with no heat shielding? If you take a long drive, then turn the car off for, lets say 6 hours, to totally cool down - does it do it then?

I like your thinking.

If the car is left to cool down ie a good 8 hours or overnight then it doesn't do it. Only does it when warmed up.

I will check the lines and see where they go and what they are close to

 

[Old Guy]

I am iffy on vapour lock as the cause of the problem. If you do the engine stop and restart and get it back to the point where the engine is operating correctly again, do an engine stop and then immediately restart. If the problem re emerges, I don't think that you have vapour lock. The quick shut down and restart should not provide enough time for heat soak to cause vapour lock. Two other factors. First, modern FI systems running at 30 - 40 psi are pretty resistant to vapour lock. You would need a really big heat source to boil the gasoline when the pressure is that high. Second, if you had vapour lock, the engine would not run or would barely run until the vapour was purged through the injectors by repeated pressurization of the fuel line by the pump and repeated restart attempts, after which the engine should run relatively normal.

Vapour lock is a problem with carburettor systems using a mechanical fuel pump driven off the camshaft. The vapour would form inside the fuel pump at which point you were totally buggered because the pump would not produce any flow until things cooled down and the vapour condensed. In the NSX, the pump is located well away from the engine, should not be subject to vapour formation and should have no problem pressurizing the fuel system to purge any potential vapour from the system.

If the hot restart problem does not emerge when you do the quick restart, and only occurs when the shut down is for a couple of minutes, then I agree you may have some kind of heat soak problem. I would still be iffy about vapour lock. One of the first and easy things to check is the manifold air temp sensor. If the air temp sensor is dirty, it reads the air temp incorrectly and can screw up the mixture which can cause poor running. There are a couple of posts on Prime dealing with the cleaning of the sensor. A factor pointing to the dirty air temp sensor is the K&N panel filter. Most people over oil these things (more is better - right?) and the excess oil gets sucked into the intake system. In fact, if the oiled element filter has been in there for a while, chances are that your throttle body will be due for a cleaning. Stick to the OEM dry pleated element filter and change it more often if you are concerned about restrictions to air flow.

A caveat about the dirty air temp sensor. Did this problem emerge overnight or has it been developing for a while? If it emerged overnight, it is likely not the air temp sensor. They don't get dirty overnight.

The NSX has a MAP, not a MAF sensor. MAP sensors tend to be pretty reliable. I would not fiddle with the TPS. If you had a TPS problem, I think that problem would persist and not come and go.

 

[vandale]

I am iffy on vapour lock as the cause of the problem. If you do the engine stop and restart and get it back to the point where the engine is operating correctly again, do an engine stop and then immediately restart. If the problem re emerges, I don't think that you have vapour lock. The quick shut down and restart should not provide enough time for heat soak to cause vapour lock. Two other factors. First, modern FI systems running at 30 - 40 psi are pretty resistant to vapour lock. You would need a really big heat source to boil the gasoline when the pressure is that high. Second, if you had vapour lock, the engine would not run or would barely run until the vapour was purged through the injectors by repeated pressurization of the fuel line by the pump and repeated restart attempts, after which the engine should run relatively normal.

..........................

I think you maybe right.

I removed the cheap generic fuel filter and installed a Honda one and without taking it for a drive I bridged the OBD connector and it was throwing a 36 which is TCS. Now this cars TCS has been disabled permanently when the ABS pump was removed and also the airbag however I found that the TCS fuse was still in the engine bay fuse box. I removed this and took it for a drive.

From cold to hot no issues. I drove medium-hard for approx 20 mins then stopped and got fuel, then restarted and no issue. I then drove approx 5km to the shops and spent 10 mins away from the car then started and no issues, then came home and parked up for 5 mins then restarted and no issues.

Touch wood its fixed. I assume the TCS system was half engaging with the fuse installed or that had nothing to do with it and it was simply a fuel issue that was rectified by a Honda fuel filter.

Time will tell I guess. I will post further info on its success or failure

Thanks

 

[Old Guy]

I think you maybe right.

Touch wood its fixed. I assume the TCS system was half engaging with the fuse installed or that had nothing to do with it and it was simply a fuel issue that was rectified by a Honda fuel filter.

Thanks

Could be. I have no idea how the TCS works on the pre drive by wire cars. Anyway, as long as it runs fine, don't look a gift horse in the mouth!

 

[vandale]

Update:

I have driven approx 50kms today since the repair and I have stopped and started approx 6 times without any issues. Am very happy.

Safe to say its fixed, touch wood!