High End Miss

[WalkyHR31]

Hi Team, I have a built S1 RB25DET that was installed in my HR31 in 2014. Engine has been running perfectly for 9 years mainly doing track work so lots of high boost and RPM. Runs 20 psi.

At a recent track day it started to miss once it got over 4500 and got worse as the revs increased. Could not get past 6000 in 2nd and 6500 in 3rd. Starts, idles and runs perfectly below 4500 under both light and heavy load. 

So changed the plugs that had been in it since it was installed with a new set of BCPR7ES gapped to 0.75, fitted a new Du-Luck R33 coil loom (original had broken plugs etc) and purchased another set of Splifire Coils to try. Every time I changed something I took it for a test run and then moved on to the next thing.Thought all that would do the trick but no, this afternoon took it for a run after changing the last 3 coils and same thing. I can check fuel pressure (have to borrow gauge) and voltages of the MAF and TPS via my ECU Talk readout, but thought I would see what you guys had to say. Thanks.

 

 

[GTSBoy]

I would have said gap the plugs down, or that the coils have gotten tired. You have covered that. Gap them down to 0.6 and see if it helps. Nothing to lose.

Do S1s still use a separate igniter? I can't remember. Worth considering.

Do an exhaust gas test on the coolant, in case you have lifted the head or otherwise damaged the gasket.

[WalkyHR31]

1 hour ago, GTSBoy said:

I would have said gap the plugs down, or that the coils have gotten tired. You have covered that. Gap them down to 0.6 and see if it helps. Nothing to lose.

Do S1s still use a separate igniter? I can't remember. Worth considering.

Do an exhaust gas test on the coolant, in case you have lifted the head or otherwise damaged the gasket.

I ran the gaps at 0.8 on my previous plugs for 9 years with no issues but can try 0.6 no problem.

Yes they do have a separate ignitor and I just happen to have a new one in my box of tricks but completely forgot so thanks for the reminder. 

How do I do the exhaust gas test?...or do you mean just let it idle with the cap off and also give it a rev to see if any bubbles?

[GTSBoy]

1 hour ago, WalkyHR31 said:

How do I do the exhaust gas test?...or do you mean just let it idle with the cap off and also give it a rev to see if any bubbles?

Test strips, like a pH tester. Looks for dissolved CO2.

[WalkyHR31]

OK thanks will try that.

I also have a spare CAS out of a S2 RB25. Would that be worth trying? I assume S1 and S2 are the same.

[GTSBoy]

1 hour ago, WalkyHR31 said:

I assume S1 and S2 are the same.

I think that can be a mistake with the CAS. There's the alloy case and the plastic case with 100% swapped wiring pins between them. If you have 2x alloy cases, I _think_ they are the same.

[WalkyHR31]

Yes both are alloy cases, so I will fit the spare and set the timing then if that doesn't fix it fit the new Ignitor. If that doesn't fix it then clean the MAF element and if that doesn't fix it then when I can get hold of the FP gauge check that (fuel pump is Walbro 255 fitted new 10 years ago but only done 20,000K's), so plenty to do. Thanks again.

[Dose Pipe Sutututu]

What ECU are you using?

Might be worthwhile pulling logs and posting them up.

Instead of just randomly replacing parts, log the following data points:

• AFR (if available)
• Timing
• RPM
• Fuel Pressure
• Load

and post it up.. will help with actual troubleshooting

[WalkyHR31]

Z32 ECU with Nistune board.

Sorry do not know how to log info. The only info I can get is via the ECU Talk display I have connected to the consult port. Maybe you could give me some pointers. Thanks

[GTSBoy]

Install Nistune on a laptop and....log.

[WalkyHR31]

OK thanks but don't have any software for it. So I guess it will have to be suck it and see!

[GTSBoy]

Personal license is $220. I can't imagine not having access to it, myself. Whenever I'm curious about a perceived engine running problem, the laptop comes out and I dive in.

[WalkyHR31]

OK but have never any any reason to need that software as engine has performed perfectly since I built it 9 years ago. I have it dynoed every 2 years to check tune etc. Now about to build RB30/25 and am going to go with a Haltec so if I can't sort it out by trying different things that I have on hand then I will get the Haltec and hook it up and check all the logs etc. Going away now for 2 weeks so will get back into it when I return but I basically won't be driving it again until track season starts March next year.

Thanks again for your help.

[WalkyHR31]

OK guys a bit of an update. Tried the new ignitor, spare CAS, fuel pressure OK at 40 psi right thur the rev range and under load. Drove it last week from my home in Maitland to SYD and miss really bad right now thru the rev range and nearly didn't make it. Engine was missing and felt like not getting fuel. 

Got to mates place (he runs an R33 GTST race car) and took front off to check timing and marks all lined up. So both of us scratching our heads. Just so happens by chance we were checking wiring and I had left the ignition on and went to check if plug was on CAS properly and when I touched it I heard the fuel pump prime. Every time I touched the plug or wiring the fuel pump would prime so obviously ignition was being turned on and off at this plug. Took off plug, peeled back insulation and low and behold one broken green wire but just enough insulation to keep it in contact until vibration or motor movement made it open circuit. then complete circuit again and so on. I guess after 30 years of heat and vibration this is bound to happen.

Now this sensor controls fuel and ignition so hence the intermittent missing and fuel starvation. Fixed wire and now back to 400 WHP and 7500 RPM no problem! Drove back home yesterday and car going like a dream. So 6 months of pain for one tiny broken wire that I only found by chance.

Hope this helps someone else chasing the dreaded RB miss!!