Mysterious big loss of power/drive on Spa circuit during parade laps.🤔

[NSXGB]

Just remember Senna was driving that day.....

With one hand on the wheel...

Come on Clive, we need more info.

[goldnsx]

This is what's happening;
http://www.nsxprime.com/forum/showth...=1#post1753619

Oh, you live and learn, I wasn't aware of that. Having changed the clutch hydraulic a decade ago the bytes and bites were stored with other things...
But my point is still that changing the clutch only doesn't have to do anything with the clutch hydraulics. If you change them too that's another story.

If this is really the case why only above 6k rpm?

[WhyOne?]

Just remember Senna was driving that day.....

I'm not so sure Jonathan....I saw Senna win the 1991 Belgian GP at Spa, driving a Honda, and he very successfully (and impressively)drove around gearbox / clutch issues.....

[Pride]

Hi guys, I've just got back from an exhausting and very stressful day at Beaulieu supercar weekend after breaking down twice.
Let me explain, but first I'd like to just say having read all your helpful posts about this problem that I've never laughed so much particularly when I read Hagasons comment about Yeomans inadvertently refitting my old clutch kit back in by mistake 😂😂😂😂😂😂 and then Britlude, "remember Senna driving was driving that day", classic 😂😂😂😂
I do hope our European friends on here understand your crazy sense of humour, I'm still chuckling while tapping this keyboard. 🤣
But honestly thanks everyone for your thoughts and input, fantastic.

Anyway this great event revolves round supercars taking it in turn to sprint up Lord Montegue's drive, noon and then 3pm.

The first run went without a hitch after ripping it up Lord M's drive when the start flag was dropped, by the way Fred (my pooch for those that don't know him) was sitting on my lap pretending to be Mutley driving the car, the crowd seemed to love it as I wheelspun away and we had almost a standing ovation on my slow return journey back down the drive where the crowd cheer and clap if they approve or stay silent if it's just average, and boy did they approve. 👏👏👏👏👏👏👏👏👏👏👏😂😂😂 thanks to Fred.🐶



The engine performed well up to the 8k red line in the first two gears at which point it's time to slow down and stop, no hint of the problem I had last weekend on that run.

I parked back into my allotted parking bay in the paddock, switched it off to cool down, ten minutes later went to start it and although it cranked very healthily with my now new Yuasa battery but it refused to fire up, after several attempts I couldn't detect any smell of petrol except for the occasional puff of white exhaust smoke, which I've never seen before and oddly enough odourless.

I began thinking I would have to get the car low loaded by Rac to get home. One more try and bingo, it fired up. Next couple of hours constantly trying it, no problems.

2.30pm queuing up for it's second run among the 30 or so cars on this run, just sitting there in the heat of the afternoon ticking over, aircon full on but with windows down so Fred and I could talk to the public lining the slip road, the engine just died and refused to fire up again.

Many people helped push me out of the line into a shady area under the monorail.
After about half an hour of scratching my head and fiddling around I decided enough was enough and I'd call out Rac.

An hour later Rac turned up, I told him what had happened and he immediately listened for the fuel pump engaging, nothing. He then went behind the passenger seat panel and found a burnt/blown micro fuse which had been temporarily fitted about 5 or 6 years ago to rectify a previous engine cutting out problem.







The temporary fuse bypassed this module which I never bothered getting replaced as I didn't know what it was:

Does anyone know what this is and what it does as I think I would like to replace it now.

Having now driven my car back from the New Forest while trying to recreate the sort of load and speeds I did at Spa, I'm now almost certain the fault has gone, so long story short, not fuel pump, not clutch or adjustment but just this little module.

Advice on this please.

Thanks again, Clive

[Hagasan]

I think that's the fuel pump relay at a glance with checking any numbers?

[Pride]

I think that's the fuel pump relay at a glance with checking any numbers?

Thats it, cheers Gary.

[goldnsx]

I'm glad you've had a great day at the event which compensated you for the hassle with your car.

Actually, the fuse didn't blow, its case was melted off due to a contact resistance problem at the red connector as it seems.

That is the fuel relay indeed but only for the second or high-power stage when the fuel pump gets the full voltage above 4k rpm.
Below, you see a picture of how it works. The fuel pump gets fed from the main relay. Two components:
1. a resistor (the big one in the engine bay above the fuel filter) and
2. a relay triggered by the ECU (at 4k rpm) to bypass the resistor. That's the relay you've shown. Without the relay the car would (should) still run which raises the question if the resistor is still in place.

Whoever worked on the electrical fuel supply and installed a tiny little fuse...no comment.
My guess is that the resistor has been removed or deactivated and the relay of the 2. stage was weak. So they bypassed all with the tiny little fuse. So the fuel pump has always been running on HIGH. More wear.
The more WOT - the higher the fuel pressure - the higher the current demand from the fuel pump. The wires/connectors couldn't cope with it in the desert-hot-like temperatures during these days. In the previous fuel-cut scenarios which started this thread the voltage drop over the fuse was big enough to restrict the fuel supply to the engine. So the theory of not enough fuel was spot on. I'd install a quality relay switched by the main relay with thicker wires. Your fuel pump could still be aged/weak...it has always been running on HIGH which covers up any problem below 4k rpm. In the next stage the problem will be shown at higher revs at higher fuel demands, not a good thing. But quite an intelligent design that you should see a fueling problem below 4k rpm FIRST.



White smoke out the exhaust is not a desireable thing. Better monitor the coolant level in the expansion tank frequently during the next weeks...

[Pride]

Thanks for the great info Thomas.

I think that all makes perfect sense in my power loss during heavy high acceleration and because it was a micro fuse the very small 20amp fuse bar of this type of fuse would get very hot and cause this total melt down over time and load.

When you said that without the relay it should still run, it didn't when this temporary fix was done a few years ago and I either forgot to replace it or because it seemed to run well without it I just carried on using the car not even thinking about it.

Only when the Rac patrol asked if I'd ever had an Rac out to this car before did I remember what he had done.

The Rac patrol did test the amperage when finished installing the larger temporary fix fuse. So at idle (6amps) and at about 4000rpm (8amps).

The resistor is still in place above the fuel filter and from memory these wires were never tampered with and the only wires that have been changed were from that fuel pump relay from behind the bulk head.

Thinking about the white smoke, it might have been that the last small connection via the melted wires and fuse allowed enough current to pass for the fuel pump to spit in some fuel momentarily as it did splutter a couple of times when trying to start it, in fact it felt just like the oldie cars with carburettor and distributor, you know, not quiet firing up.

[goldnsx]

The Rac patrol did test the amperage when finished installing the larger temporary fix fuse. So at idle (6amps) and at about 4000rpm (8amps).

Hi Clive

Supplied by the main relay (only) the values are about 7 V and 4 A.

That's about right for an OEM fuel pump for the HIGH stage. All aftermarket fuel pump draw more current which the stock wiring can't handle. Honda used a Denso fuel pump (not commercially available) and the special feature about it is that it draws so little current regarding the amount of fuel it has to supply. So Honda went with an appropriate but too thin wiring diameter (too thin for the current-hungry aftermarket fuel pump). Just a sidenote.

Your actual solution still seems a band-aid to me. The car runs fine now. But the plastic impellers of the fuel pump DO wear out over time and miles. Every NSX with over 125k miles (or even less like 100k) on it is likely to have a weak fuel pump. It's a consumable like brake pads. Therefore you should address the fuel pump before running into similar problems soon.

Last year, my aftermarket 'quality' relay gave up while driving but it has to cope with 16-19A for the supra fuel pump permanently. I was glad that the engine just stalled while cruising at 2k rpm and very light throttle. Same problem: contact resistance within the relay, melted, lost connection. If it happened at redline WOT the CTSC would have blown up the engine/headgasket. Please make sure you're going to address the fuel pump to avoid any other problems. If you're going with an aftermarket fuel pump you have to upgrade the wiring anyway.

[Pride]

If I was to test the old relay would you have any idea of what the reading should be across what terminals with my meter??

Attachment 13539

Thanks.