Engine refuses to Rev.

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Tonyd

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226
Location
UK
Following my recent problem with the Lexus V8 in Cobra number 1 ( rectification not yet attempted as Car is 1.5 hours away), I now have a serious problem with the Lexus Engine in Cobra number 2.

The car starts great and idles just a little roughly.

However when you try to increase the revs it just dies.

Revs with easy start down its throat like a good but will not respond to the throttle at all apart from dying.

I have checked the complete fuel system any number of times and flow and pressure is good using the original Lexus fuel pump set at 12 volts. I tried a second spare Lexus fuel pump just in case and no improvement.

Originally it had a crank sensor problem which stopped it starting, , which I have fixed, and the only fault code to come up is code 31 which is MAF sensor related, maf sensor wiring or ecu related .

I have tried the car with a number of different MAF's , one I know is good and I have even invested in a brand new one from AIP electronics in the USA.

Every single one makes buggar all difference even the new one, and code 31 still flashes.

I have replaced all the wiring from the ECU to the Maf and it still hasn't made a jot of difference.

I have played with the tps settings and it made buggar all difference.

The ECu and loom came from a Lexus I have been driving for the last 8 years which was a great runner, without any problems whatsoever and which I stripped myself on my drive at home.

The ECU was perfect coming out of the donor vehicle and between being removed from the donor car and being installed in the Cobra the ECU and loom just sat in a cupboard in the garage so there should be little reason to doubt the ECU's health.

Anyone got any ideas.

I have been postponing the UK's Kit car test, the IVA, for this Cobra for the last month to try and get this engine running properly but have so far failed to do so and am now getting heartily fed up with the thing.

Anyone got any ideas as to what could be the problem or any avenues of investigation to try.

Cheers,

Tony
 
Update need to check ECU.

Update

Rechecked everything and only fault codes are 31, 24 and 47 all relate to the MAF and TPS.

MAF and TPS share common 5 volt supply which is good, all earths are good and I have renewed all wiring from MAF to ECU.

I need to check ECU operation and I would hope I can do this using my mates ECU in the other Cobra.

All the part numbers match on the two ecu's apart from the final digit on the final number ie m the numbers are 89661 - 50160 and 175000- and then 5213 on one ECU and 5214 on the other.

Are they compatible and can I use one to check if the other's ok?

Cheers,

Tony
 
They will be fine to swap. The number that counts is the toyota number 89661 (covers all toyota engine ECUs) Then 50 (celsior/LS400) 160 ecu number. The last number (0) will change to 1 then 2 as the ECU is updated in a model so also swap fine. Cheers
 
Hi, Thanks for that.

A very knid friend over here has provided me with an exact match for my ECU and his ECU has exactly the same result as mnone so I can deduce that its not an ECU problem its a wiring problem that I have created that triggers phantom MAF and TPS fault codes.

So, time to rip out all my wiring and check it all again and refit.

Cheers,

Tony
 
Have ripped out all wiring and started again , rechecked everything umpteem times. No matter what ecu I use the same results, car starts but will not rev and with my mates ecu it wont even idle.........

Anyone know what would make the ECU refuse to fire the injectors once it has started.......the start is no problem it just dies immediately afterwards.

Fault code still 31 and 47 although theres 5 volts to both and the earths are good.

Anyone have any ideas whatsoever why the ECU is refusing to recognise the signals that must be coming in from a new AFM and a known good TPS.

Cheers,

Tony
 
Firing into life then immediately stalling is generally a coil fault caused by the ecu shutting the fuel due to a fault signals by the ignitor feedback loop. Also check the ignitors are well earthed. Ignitors do fail but not that often.

That ecu should rev fine (well sort of fine) without the AFM plugged in.

The code 47 is sub TBS so there might be a chance it is detecting the traction control is coming on. unplugging it should also eliminate it as an issue. I run the engines fine without the sub tbs.

Does you ECU set other codes when you cause faults? eg unplug a cam sensor and see if the ECU throws a cam sensor code? Likewise unplugging the AFM should also result in a air temp sensor code.

Have you plugged your ECU into your mates car?
 
Firing into life then immediately stalling is generally a coil fault caused by the ecu shutting the fuel due to a fault signals by the ignitor feedback loop. Also check the ignitors are well earthed. Ignitors do fail but not that often.

That ecu should rev fine (well sort of fine) without the AFM plugged in.

The code 47 is sub TBS so there might be a chance it is detecting the traction control is coming on. unplugging it should also eliminate it as an issue. I run the engines fine without the sub tbs.

Does you ECU set other codes when you cause faults? eg unplug a cam sensor and see if the ECU throws a cam sensor code? Likewise unplugging the AFM should also result in a air temp sensor code.

Have you plugged your ECU into your mates car?

My Ecu was perfect three months ago ( as was for the 8 years we had it previously) when I drove the car back to my house and stripped it on the drive.

I was sure the ecu was ok and that was confirmed when my mates ECu also demonstrated the same behaviour when installed in my car. The chances that my ecu developed a fault within it and his developed the same fault is practically nil.

The ecu does throw other fault codes if provoked (eg unplug the MAF and the air temp code comes up). So the ecu is reading the temp sender part of the MAF but not the airflow itself. And as you say the engine should run without most things connected, just not very well.

The Ecu and intake came from a non traction control car so theres just the one TPS although looking at the wiring diagram theeres still the requiremnt to have power fed down the VTA 2 wire.

The ignitors are good and earthed correctly. Would a duffff coil throw a fault code, as the ECu has thrown a fault code for a failed crankshaft sensor which I have replaced.

The engine runs happily if I put easystart ( start ya bastartd for those down under) down its neck but not with its own fuel supply which is fine for both quantity and pressure.

Its a real teaser this one.

One thing that I though unusual is that when I'm checking the injector voltages when the innition is turned on theres 12 volt showing on both sides of the injector plug.

Now one side I can understand but the ECu fires the injectors by earthing each injector from its common black/ orage power feed. I was expecting to see non-continuity to earth ( unless its firing) on the wire from the ECU, certainly not 12 volt coming up the wire in "the wrong direction".

Well the black and orange feed is OK, but should there be 12v coming from the wire from the ECU to each injector.

Could this be the problem and if so how come the engine starts and idles but dies under any other throttle opening? Is the start and idle circuit in the ecu totally seperate from the normal circuit ie over 750rpm

I'm convinced that I have stuffed up the wiring somewhere but the loom came complete from the donor car , so I have not cut anything out of it. It will probably hit me in the face like a brick when I fathom it out but in the meantime its proving a huge pain in the bum.

Cheers,

Tony
 
Back to electrical basic's 101 with your suggestions of the injectors having power on both sides. This is not unusual at all. Check out how basic circuits work.

With a problem like this I would be fitting a pair of new coils , even if that isnt the problem it's a easy check and I always have new coils on the shelf as I replace that many.

The sub TBS code is interesting from a non traction engine , maybe there is a problem with that wiring. Have you checked the voltage and earth at the IDL2 and VTA2 pins? And maybe inside the ecu as I have seen lots of poor connections at the ECU header plug.
 
Back to electrical basic's 101 with your suggestions of the injectors having power on both sides. This is not unusual at all. Check out how basic circuits work.

With a problem like this I would be fitting a pair of new coils , even if that isnt the problem it's a easy check and I always have new coils on the shelf as I replace that many.

The sub TBS code is interesting from a non traction engine , maybe there is a problem with that wiring. Have you checked the voltage and earth at the IDL2 and VTA2 pins? And maybe inside the ecu as I have seen lots of poor connections at the ECU header plug.

Hi,

Tried the new coils yesterday evening, no change. Car still starts lovely and then refuses to run. Voltage at VTA2 bang on 5 Volts and earth good on IDL2.

I opened up Lexus ECU once and had a look inside but quickly closed the lid again before I let all the magic smoke out.

If there's anything wrong with the ecu, which I doubt as two ecus would have had to fail simultaneously with exactly the same problem, I'll be getting someone who knows about electronic thingymajigs to fix it.

Any more ideas please keep them coming.

I shall prevail, I shalll not give up, I will overcome..........

Cheers,

Tony
 
The fuel pump is activated at high speed when the engine cranks and will have residual pressure for a few seconds after it starts.

Once started it switches to low speed.

I've had it before where the engine would start then die.

I found the fuel pump resistor was faulty (an early Crown engine) and by shorting it out the engine kept running.

Whilst I wouldn't recommend it to drive have you tried hot wiring the fuel pump so it runs all the time then starting the engine?
 
The fuel pump is activated at high speed when the engine cranks and will have residual pressure for a few seconds after it starts.

Once started it switches to low speed.

I've had it before where the engine would start then die.

I found the fuel pump resistor was faulty (an early Crown engine) and by shorting it out the engine kept running.

Whilst I wouldn't recommend it to drive have you tried hot wiring the fuel pump so it runs all the time then starting the engine?

The way I wire my cars up is that I have the fuel pump running off a relay triggered by the ignition switch at the full 12v constant, rather than the 9v rising to 12 when the engine is under demand, which is in turn ( once the set up is running perfectly) protected by an inertia switch. Noise is not a factor in a Cobra as tyre noise drowns out the in-tank pump.

Thus at the moment the pump is going permanently at full chat so there's never a shortage of fuel and the fuel rail is at full pressure. Even if I clamp the return pipe, with the pump going hell for leather in the tank, the engine will still start but not run or rev. I have tried spare pumps to no avail. Petrol supply is not a problem.

So something, somewhere is allowing the engine to start, idle albeit roughly for a few seconds and then it dies if you even try to crack open the throttle.

The ECU is a 93 and wired up exacly as I wired up the first 93 in our first Cobra which my mate has run without problem for the last 6 years. I have tried a second good ecu with the same results so its not an ecu problem.

The ECu, loom etc has come from a perfect LS400 we had run as a snotter and daily car for 8 years without any problems which I drove here and stripped on my drive three months ago.

The Ignitors are good and I have tried changing the coils but with no improvement.

Next on the list is the cam sensors as they are 90 vintage like the engine and oerhaps the ecu doesnt like them for some reason although no cam sensor logged as fault codes, just 31 MAf sensor.

The crank sensor and maf sensor are new. The tps works, all sensors are getting 5 volts, all earths are good, the coils and ignitors are good , engine revs lovely with easy start down its neck but the injectors dont want to put fuel into the engine for some reason.

Will report back once I've changed the cam sensors.( which entails changing that part of wiring loom as the plugs are different......).

If that doesnt work its then down to chasing every pertinent wire in the loom to ensure continuity, but having done this for the MAF, TPS, Idle Control Valve, theres not many left to try.

If only I had an idea of how the internal ECU programmes work ie what inputs are needed for the injectors to fire, I could narrow down the search but unfortunately I dont.

Still no worries, I'm not beaten and it will get sorted eventually.

Any further ideas please keep 'em coming.


Cheers,

Tony
 
Changed the cam sensors and guess what........?



The thing now wont start at all.


Now nursing a beer 'cos tomorrow I will be reversing everything I have done today.

I'm sure I can hear that engine laughing at me through the garage door............

Cheers,

Tony
 
Have you checked the injectors are firing after it starts?

It could be running on fuel from the cold start injector.

I'd try disconnecting an injector and use a small light to see if the injector is being fired.

Google "Noid Light" as I may not have explained that too well.

You need to identify where the problem is before puling it all apart and re-doing it.
 
It doesn't have a cold start injector.

So the injectors fire in fuel to start the thing but then stop firing at all.

I'll be putting the cam sensors back in so it gets back to starting.

Then I'll continue with the chasing down of the problem.

Its a bit of a quandry isn't it.

Cheers,

Tony
 
I think I once read that the injectors will stop firing if the spark stops.

It may be worth checking if that's true (I'll have a look as well) as that may be a good place to start looking.
 
Yes I read that thread right at the beguinning of my problems.

I fixed one Lexus Cobra this wekend that had a duff efi coolant sensor but which threw MAf and crank sensor fault codes .

Learning from that experience I will now assume every sensor is knackered unless proven otherwise.

Tomorrow I will be putting in a new efi coolant sensor just so I have a base line of good parts to work with. The crank sensor is new, the cam sensors are good and work, the maf is new, but the EFi coolant sensor is the same age as the duff one I just swapped out in my mates Lexus Cobra so putting in a new one is a good insurance policy.

It appears that a bust efi sensor can trigger a heap of unwarranted and bogus fault codes.

Cheers,

Tony
 
Well tried a new efi temp sensor but the car still fires up but then refuses to run.

Must be some form of wiring fault stopping fuel injectors firing.

Time to start checking out each and every wire..............

Chers,

Tony
 
Tony,

Are you 100% sure the injectors aren't firing at all?

If they are working to get it started then they work.

What you need to sort is why they stop functioning and that is usually ignition fault driven.
 
Tony,

Are you 100% sure the injectors aren't firing at all?

If they are working to get it started then they work.

What you need to sort is why they stop functioning and that is usually ignition fault driven.

The injectors are firing at start but then stop firing immediately the engine starts. The fuel injectors work at start but not in run.

Put fuel down its neck and it runs happily.

The ecu, injectors, engine and gearbox loom, ignitors and coils, induction plenum, throttle body, TPS, ICV all came from a car that was running perfectly, that we had had for some 8 years as a daily driver, and which I stripped here personally. All earths are good, the engine is well earthed as is the ecu, the engine loom itself, the ignitors etc.

Hence if there is some communication missing from the ignition system back to the ECu to fire the fuel injectors I cannot see why it is not contained in the engine loom which is exactly the same as it came out of the donor car.

This is why it must be a wiring fault ( break) somewhere in the loom but I will be going over the ignition system with a fine toothcomb as the first port of call.

It does appear that the ecu is not getting a" I've started so I must continue to run" type of signal. Instead its actually saying "I've started but I'm not running now because I dont have a signal."

Any idea what wire that "continue to run signal" would be going down into the ECU? Where does the feedbacl loop from the ignition system run?

No need to tell me the actual pin just the wiring shorthand ID would do as I have enough wiring diagrams here to chase the actual wire and pin down.

One thing to mull over is that recently the engine started, idled but refused to rev, now it starts but refuses to idle.

Thank God for beer. Time to get one.

Cheers,

Tony
 


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