Random cutting out

[Danger Mouse]

Back to the forum with another problem... kinda forgotten I was a member...

So been trying to track down a long-term issue, where the engine will just randomly die while driving. Does it at any revs, any speed and the rev counter immediately drops to zero. Often it will recover itself, as it's only a temporary cutout, but sometimes it takes a bit longer to recover and I end up on the side of the road trying to restart it. When it is really bad, it will cough back into life, then just die again, but usually it eventually fires and I can continue driving for a while (it will come back quickly when it's at it's worst).

I've had 3 auto sparkies look at it, nothing obvious. I thought it might be the crank angle sensor, but I have put in a known good one and it still does it. Have also swapped out the AFM for a known good one (didn't think that was the issue, but it was cheap), as well as replaced all the leaky caps in the ECU (none were showing signs of leaking, however).

As I continue to work through replacing bits, maybe someone on here has some suggestions. What ever is causing it, it's creating a total loss to the ignition system, hence the dead rev counter (I can coast in gear, so I know the engine is turning over, but the rev counter is on zero). I have read somewhere that if fuel pressure drops below a certain level, it cuts the engine to protect it from fuel starvation damage, so next on the list is replacing the external fuel pump (that is noisy as anything, so I can certainly hear it working, but that doesn't mean it's working efficiently).

Any ideas? I can't trust the thing as it is, although I drove it for 2 hours last weekend non-stop and it didn't even cough once. My journey to work this morning (stupidly thought it was behaving after last weekend) it was cutting out regularly. Stupid intermittent fault...

 

[George_R]

non-FSE engines of Toyota don't have fuel pressure sensor, so it's not ECU who "cuts the engine to protect it from fuel starvation damage"

I would suspect wiring rather than sensors. With no additoonal info I would suspect CAS wiring, power source to ECU, and power source to ignition system.

I would first arrange scanner , if available, and see if it still reads RPM when the problem occurs. If it does, then it's ultimately the ignition system wiring.

Next, I would run a temporary ignition system wiring to bypass factory power source and see if the problem persists or not.

 

[cribbj]

As George said, I'd suspect an intermittent in the wiring. Wiggle connectors, starting at the ECU and see if you can reproduce it.

 

[Danger Mouse]

Cheers for the replies guys. Done plenty of wiggling of wiring, but it's hard to replicate and doesn't seem to solve the issue. Does make sense though, especially as it is showing typical CAS symptoms, ie for the most part restarting straight away.

Power to ECU and ignition has been redone by the last sparky, he was awesome and found a lot of shitty wiring under the dash, fixed that up and thought he'd solved it. Sadly, he didn't.

Good news about the fuel pressure sensor, was kind of getting desperate so was looking at every 1UZ post on the internet and got it wrong. I can stop going down that dead end now...

No OBD port with this conversion, so no error codes or scans to point me in the right direction.

 

[George_R]

then make yourself one! It's really useful. At least wire up the warning light and some sort of switch which would connect ECU terminals labeled TC and E1.

 

[Danger Mouse]

then make yourself one! It's really useful. At least wire up the warning light and some sort of switch which would connect ECU terminals labeled TC and E1.

Ah yes kind of obvious I need to do this, could stop me chasing my tail

So the switch is to essentially switch in and out a jumper between TC and E1? The engine light it wired up, so if I jumper those terminals I should get the engine light flashes? Or do I need to wire up a different light (sorry, I'm a pretty average mechanic, but a well below average auto electrician).

I've seen a few threads talking about wiring in an OBD port but none about how to. The above is probably a bit more simple if I'm understanding it right. I like simple.

 

[George_R]

Yes, just a switchable jumper from TC to E1 , or from TE1 to E1 (depends on model year: your wiring diagram will show only one of these options).

Regarding the OBD port, I'm not very familiar with which scanners are good for non-JDM non-vvti engines. But the other useful pins are TE2, VF1 and VF2, you can use a multi-meter against them to "read" the fuel trims, which in turn are essential in troubleshooting MAF, O2 sensors and a number of other things

 

[Danger Mouse]

Thanks George, very helpful

The engine and loom/Ecu are from an early JDM Toyota Crown Majesta, which caused all sorts of issues when I went to replace the alternator as it uses a smaller alternator to the off the shelf LS/SC400 ones, which I didn't have room to fit. Perfect for tight engine bays though, especially with the factory block hugger headers. Has a 3 plug ECU too, which tucks away nicely under the dashboard.

Anyway, I have a jumper switch to wire up

 

[Vate]

Did you ever find out what was causing the problem?

 

[Danger Mouse]

Did you ever find out what was causing the problem?

No, see my thread in the FIAT section.

Basically ended up at my favourite auto electrician (he really is awesome), talked about wiring in the OBD port and a few other plans, but he reckoned he could waste a lot of time and charge me a lot of money to possibly not even sort. So I followed his advice and junked the ECU and loom for a Megasquirt,which I'm part way through fitting.

Interestingly though, I tried wiring in the OBD port myself and I don't know what ECU I have, but it matches absolutely none of the pin out diagrams I've found on the internet. Didn't want to jumper pins without being sure, so gave up. The fun of having the rare, early JDM Crown Majesta set-up.

 

[cribbj]

Had a very similar issue with a first generation AEM that I had installed in my Supra by one of the better AEM tuners. Turned out to be a misfitting pin/connector between the harness and ECU.

The car would simply cut out and die randomly. Only by wiggling conductors at the back of the harness ECU connection did I finally narrow it down.

And this was with a brand new Toyota harness, so I put the blame on the AEM side

 

[Danger Mouse]

Yeah sucks balls when it's an intermittent problem, mine was either loom or connector I reckon, but wasn't going to waste money trying to figure it out.

When I was a service and calibration tech in the early days of my electronics career, it was amazing how much stuff we fixed by wiggling things

 

[Saint]

Have you tried adjusting your electronic throttle bodies?