Project Laurel: How many false positives?

Project Laurel: How many false positives?

I haven't posted about this project for some time now. The reason for this is because I've been struggling to find the cause of an issue.

Following my previous post where I had rebuilt the engine with a new head gasket and it was running again, I then managed one good drive before it started acting up again! The second time I took it out I drove to an exhaust specialist to have a silencer installed to try and quieten down the exhaust a bit. On the way there I noticed that at idle, if I wasn't careful the engine would idle so low that it would stall. This was really strange, had I messed something up that didn't appear straight away? Or was this a new problem?

The first thing I did was a lot of googling, which probably wasn't a good idea. It's a bit like Googling when you have a sore throat, the results tell you have anything from a mild cold to galloping Gonorrhea! In the case of my poor engine it was everything from a split hose to head gasket (again? surely not?!!) Thankfully I was sensible and started working through the simplest issues first. In order for a car to run and idle properly it needs three things, fuel, air, and spark.

I had a new fuel filter waiting to go on so I changed that just to be sure and then checked the fuel pressure to the rail. So I had fuel, all good there!

Next was spark, I'd put new spark plugs in it when I rebuilt the engine so I checked them and they were a pretty sooty but otherwise okay, but just to be sure I swapped out the standard coils, wiring and ignitor amp for a much simpler set of smart coils from an Audi R8, along with a wiring loom from a guy making conversion kits online and a bracket that was meant for an RB25 but still worked, I also swapped out the spark plugs for some new ones, and made sure the gap was correct. So now I have fuel AND a strong spark, but still the engine wouldn't fire what else could it be?

R8 coil packs

The only thing left was air so I started by unplugging the MAF to and suddenly the car fired into life! Is that it? Was the MAF dead? .... No, four MAF's later (Yes I managed to find four, two thanks to Garage D!) and it still wouldn't fire! So that wasn't the problem.

MAF

Next a friend told me that sometimes the Nissan engine won't start if the stock water temp sensor is bad, so since it was cheap I replaced that, but still no luck! I was also told by someone else (can't remember who) that if the cold start valve has gone bad that can cause it to not start, and to test it you unplug it I did this and still nothing! I also took off and cleaned up the idle air control valve, but still no joy!

After jumping on the Driftworks forums and chatting to a few people I was told to check the MAF wiring, sadly (because I was getting desperate at this point!) there was nothing wrong it!

After a couple more weeks of no progress and starting to get frustrated I decided I was going to delete the cold start valve and give the idle air control valve another clean. It was at this point I found the source of all my problems, upon removing the throttle body to get access to the cold start valve I noticed that one of the hoses to the cold start valve had a huge split in it! On closer inspection it turned out to the be the one going from the valve to the intake plenum, when I got the hose off I realised that it was rock solid which explained why it had cracked in this way. Needless to say I was pleased with my decision to delete the cold start valve!

Holey Hosey

Broken hose

After blocking off both ends where the valve connected and puting everything back together I tried starting her up again and low nad behold she purred like a kitten once more!

From the start I'd had people telling me its likely to be a split hose or pipe, and because I thought I'd checked them all I shrugged this theory off, but as it turns out I should have been more thorough with my search as I could have saved myself three months of frustration!