Strange issue RB25DET wont start

[jtha7]

Hi all,

Im sorry for the long post im hoping someone may have the solution to my car not starting. Ive been restoring a 1994 R33 GTST (Series 1) for a few months. 

The Issue: 

- When everything's together on the fuel rail the car cranks but wont start.

- but when I disconnect the fuel pump and hold throttle open it will be hard but it will start. I can then put the plug back on and the car will run normal. If i turn it off and try again it wont be able to start.

- this first started when my mechanic and I put the intake back on (after fixing coolant leaks), then for some reason when I changed a fuel dampener on the return line the Issue temporary resolved but came back a week later.

 

Things about the car:

- it sat for about 4 years but was able to start and run (it had a coolant leak back then which was from corrosion. All cooling system has been fixed)

- replaced the old fuel and the fuel pump as it stopped working, i replaced it with the same size fuel pump it had which was a walbro 255 

- alot of things have been replaced, timing belt, splitfire coilpacks, spark plugs, Rocker gaskets. Basically alot of things have been refreshed and the car was running fine.

- It ran for a week well after replacing the fuel dampener. Then same issue arose. I replaced FPR with a SARD FPR, also replaced the injectors and rail (also verified that the injectors were working), checked spark looks ok (maybe a bit weak). Ive cleaned up all the grounds too.

- ive tested all the lines (return and inlet are not blocked.)

 

I've heard that it could be fuel pump losing voltage during cranking? (I can ground the grey wire on the fuel pump plug) but this doesn't make sense as ive got constant fuel pressure on my gauge and the car will be able to start when there's no fuel going into the rail (it can start also if i just run inlet into the return). So i think this points to too much fuel/not enough spark.

At this point im thinking to just recheck my grounds and possibly any sensors.

Please share any help. TIA

[Murray_Calavera]

What ECU?

[jtha7]

Stock ECU

[Murray_Calavera]

17 hours ago, jtha7 said:

ive got constant fuel pressure on my gauge

What's the fuel pressure while the car is cranking?

17 hours ago, jtha7 said:

replacing the fuel dampener

Curious, why did you replace the fuel damper?

17 hours ago, jtha7 said:

also replaced the injectors

What injectors are you using, are they brand new?

[jtha7]

So I put it to 3bar (43.5psi) while priming. It stays at 43.5~ as I crank shakes slightly. Ive also tried dropping pressure to see if that changes anything.

I replaced the fuel dampener because I was troubleshooting the system along with the stock FPR (swapping them one by one to rule them out). But i only got up to changing the dampener and it started running again.

Injectors are stock second hand. I did a bench test on both my original ones and the secondhand ones. The second hand injectors I have in the car now spray slightly stronger than my original injectors.

[GTSBoy]

Put the original injectors back in. See what happens.

[MBS206]

What do the spark plugs look like after you tried to start it with everything connected?

[jtha7]

Also wanted to say, my new spark plugs are blackened looks like it's very rich. I have splitfire coilpacks but stock coilpack loom and ignitor. I tried directly grounding the ignitor ground to body as well. 

Edited October 7 by jtha7
Typo meant ignitor ground not coilpack ground

[MBS206]

31 minutes ago, jtha7 said:

Also wanted to say, my new spark plugs are blackened looks like it's very rich. I have splitfire coilpacks but stock coilpack loom and ignitor. I tried directly grounding the ignitor ground to body as well. 

What do they look like right after you've tried to start it with everything connected?
Also post photos of what they actually look like.

[jtha7]

Hi sorry late reply I didnt get a chance to take any pics (my mechanics on the other side of the city) but the plugs were fouled from being too rich.

I noticed the MAF wasn't genuine, so I replaced it with a genuine green label unit. I also swapped in a different ignitor, but the issue remains.

I've narrowed it down a bit now:

- If I unplug and reconnect the fuel lines and install fresh spark plugs, the car starts right up and runs perfectly. Took it around the block with no issues

- As soon as I shut it off and try to restart, it won't start again

- Fuel pressure while cranking is steady around 40 psi, injectors have good spray, return line is clear, and the FPR vacuum is working. It just seems like it's getting flooded after the first start

I unplugged coolant sensors to see if its related to ECU flooding but that didnt make a difference. Im thinking its related to this because this issue only started happening after fixing coolant leaks and replacing the bottom part of the stock manifolds coolant pipe. My mechanic took off the inlet to get to get to do these repairs.

My mechanics actually just an old mate who's retired now so ill be taking it to a different mechanic who i know has exp with RBs to see if they find anything.

If you have any ideas please send em lll give it a try.

Ive tried other things like swapping the injectors, fuel rail, different fuel pressure regs, different ignitor, spark plugs, comp test and MAF but the same issue persists.

[jtha7]

Ps i found the below forum and it seems to be the same scenario Im dealing with. Going to check my ECU coolant temp wire tomorrow 

 

From NICOclub forum:

s1 RB25det flooding at start up

Thu Apr 11, 2013 7:23 am

I am completely lost on this. Car ran perfectly fine when I parked it at the end of the year. I took the engine out and painted the engine bay, and put a fuel cell with an inline walbro 255 instead of the in tank unit I had last year. After reinstalling everything, the engine floods when the fuel pump primes. if i pull the fuel pump fuse it'll start, and as soon as I put the fuse back in it starts running ridiculously rich. I checked the tps voltage, and its fine. Cleaned the maf as it had some dust from sitting on a shelf all winter, fuel pressure is correct while running, but wont fire until there is less than 5psi in the lines. The fuel lines are run correctly. I have found a few threads with the same problem but no actual explanation of what fixed it, the threads just ended. Any help would be appreciated.

Rb25det s1

walbro255 fuel pump

nismo fpr

holset hx35 turbo

fmic

3" exhaust

freddy intake manifold

q45tb

q45 maf

 

Re: s1 RB25det flooding at start up

Fri Apr 12, 2013 5:07 am

No, I didn't. I found the problem though. There was a break in one of the ecu coolant temp sensor wires. Once it was repaired it fired right up with no problems. I would have never thought a non working coolant temp sensor would have caused such an issue.

[jtha7]

PROBLEM WAS BROKEN COOLANT SENSOR!!!

Replaced with a new one and its running mint.

[Duncan]

Good work, and thanks for posting up your solution for future people!

[MBS206]

Interesting a broken coolant temp sensor stopped it starting!

I left mine unplugged years ago on an R33 S1. Started fine, just idled unhappy once warm

[GTSBoy]

51 minutes ago, MBS206 said:

Interesting a broken coolant temp sensor stopped it starting!

Yeah, I would have said the same. It makes me suggest that there are other things wrong, such that the ECU is totally unhappy with the broken sensor. The only other thought here is that maybe it is shorted, which might cause a different issue to the typical "disconnected" sensor.

[Kinkstaah]

I've seen similar actually in my situation. You never know what tables are attempted to be used when the car thinks it's -99C or +200C. The fail state is not usually that extreme but you know what I mean - it was in my case though!

This is where being able to read all the sensors is useful cause you see this stuff really quickly.