Engine *sometimes* fails to pull from low revs

[brman]

I am after a few ideas on what to look at next.....

The car in question is a toyota yaris petrol (1.0). In general it runs fine, pulling from tickover without any problems (for a little 1L engine anyway). However, when warm (ie never when cold) it will refuse to pull at all if the revs are too low (say below 1500rpm). Foot flat to the floor and it struggles to maintain speed. When this happens, de-clutching allows it to rev and it will normally pull when the clutch it released although it can still feel sluggish.
Often this happens when pulling out of junctions and sods laws says it is just when a lorry is bearing down on me which can make things a bit exciting.
It also never happens if the revs are kept over about 2500rpm when pulling away.

So, what to do to find the cause and fix it?
Things I have done so far:
- used a cheapo reader to check for codes. None recorded (and no engine light). However real time data shows the ignition being massively retarded (ie around zero btdc) when the problem occurs. Nothing else looks odd, although it is difficult to read the data and drive at the same time!
- replaced the camshaft position sensor (it was leaking oil)
- replaced the MAF sensor. Nothing obviously wrong with the old one
- replaced the knock sensor. Again, nothing wrong with the old one
- replaced the temperature sensor. Again, nothing wrong, just getting desperate....

Plugs were replaced about 6 months ago and show no problems.
Emissions at the last MOT were well within limits (lambda = 1.0) and the place that did the MOT took it for a test drive and (predictably) failed to notice any problem. The garage also claimed to check for codes but, as they didn't charge me, I have my doubts.

Any ideas?

[Peanut Gallery]

May I ask how old the car is?

I'm starting to think it may need a software upgrade - similar issue to the stig being unable to drive up a hill in a small car.

Edit - thinking about it again, maybe not.. data log from a odb / phone app and see if you can pinpoint a reason?

Edited by Peanut Gallery on Wednesday 27th April 09:57

[brman]

Peanut Gallery said:

May I ask how old the car is?

I'm starting to think it may need a software upgrade - similar issue to the stig being unable to drive up a hill in a small car.

Edit - thinking about it again, maybe not.. data log from a odb / phone app and see if you can pinpoint a reason?

Edited by Peanut Gallery on Wednesday 27th April 09:57

2004 with 55k miles on the clock. I do vaguely remember something in the press about a small car not going up hills. Was it a citroen C1 or something?
I am assuming not though as I have posted this on a yaris forum and didn't get loads of people saying "mine does this".

I might have to try a better app for the ODBII, do you know one that does decent data logging?

I was thinking that it might be knocking at low revs (or faulty knock sensor, hence changing it) but I cannot hear anything obvious. My current ODB app doesn't appear to show the knock sensor reading though.

[Mr2Mike]

brman said:

2004 with 55k miles on the clock. I do vaguely remember something in the press about a small car not going up hills. Was it a citroen C1 or something?

It was the new Fiat 500 with the EU6 compliant 1.2L engine. It had an enormous flat spot that made pulling away on a steep hill virtually impossible.

The problem you have appears to be very common on the older 1.0L Yaris, but with no obvious smoking gun. The lack of power suggests the engine is probably running lean under those conditions, so it's likely to either be either unmetered air (e.g. air leak) or not enough fuel (e.g. sensor fault, low fuel pressure, partially blocked injectors etc.).

[brman]

Mr2Mike said:

It was the new Fiat 500 with the EU6 compliant 1.2L engine. It had an enormous flat spot that made pulling away on a steep hill virtually impossible.

The problem you have appears to be very common on the older 1.0L Yaris, but with no obvious smoking gun. The lack of power suggests the engine is probably running lean under those conditions, so it's likely to either be either unmetered air (e.g. air leak) or not enough fuel (e.g. sensor fault, low fuel pressure, partially blocked injectors etc.).

Interesting, thanks. Shame there is no common cause

It sounds like I need another go with the ODB reader and see if I can detect any more symptoms.
I'll also have a good check around for air leaks.
it does feel like a sensor type fault to me. ie it appears to happen randomly. Sometimes it is fine, others not. Plus there is the huge negative swing in the ignition timing when it goes wrong. The only thing I can say for sure is that it never happens when the engine is cold. I am wondering if that is because it uses a different, perhaps open loop, map on cold running? Or perhaps just that it runs rich then anyway so it is a running lean problem like you say.

It also doesn't really feel like a flat spot - more like I haven't even put my foot on the throttle at all.

Actually, thinking about it, what symptoms would a faulty crank sensor give?

bring back carbs and dizzy's. They were easy to fix.......

[Peanut Gallery]

I remember watching this vid - https://www.youtube.com/watch?v=qSOm1x9a_Is&ap... - in the comments he says:
"I'm using Motorola Xoom + Torque App + OBD bluetooth adapter"

Yes, the stig was in the Fiat 500, however I drove a small chevrolet of similar age, and when you mixed a certain rev with a certain throttle position - not much happened. Eventually the revs would build or drop a bit and it would get wake up. - However being intermittent does blow this theory out of the water.

As Mr2Mike says a blocked injector / fuel pressure issue. A tank of V-Power / injector cleaner snake oil run through it?
If it does not work, cost was less than a tenner.

You have just mentioned crank sensor, someone else had one that kept failing when up to temp, get the car recovered, test it, works fine due to being cold, you get the idea!

[brman]

I am pretty sure it is the torque app I have on my tablet. I'll have to dig it out and have another play.

I also forgot to mention, it has numerous tanks of V-power and quite a few shots of redex. None appeared to make much difference although my wife now reckons it is actually worse on super than standard now. Not sure I agree with her though.

[brman]

well, I just had another very quick look at it (my wife drives it normally so I don't get a look in).
Some of the vacuum hoses do look a little perished at the end but no sign of anything that could cause a leak.
I also pulled out the plugs. These are about 3000 miles old and look ok but not as clean as I would expect. Carbon deposits I expect (it normally does very short journeys so running cold/rich) but am I being paranoid or does this show signs of running too hot and detonating? btw. the plug is much more white than shown here, the red tinge is my camera getting the white balance wrong. The little specs on the insulator and ground electrode are white.


So this points to what has already been said, running lean for some reason? Question is why? I could try some colder plugs but I am not sure whether that would help?

[Mr2Mike]

brman said:

Actually, thinking about it, what symptoms would a faulty crank sensor give?

With no way for the ECU to determine engine position, it would simply stop running. This would likely leave a code stored however.

[brman]

Mr2Mike said:

With no way for the ECU to determine engine position, it would simply stop running. This would likely leave a code stored however.

I have admit that is what I thought, I have just read people saying it will cause it to go into limp-home mode and always wondered how it would manage to keep and sort of timing at all.

[S0 What]

Check the timming chain tension, sometimes it will throw a code up saying cam and crank sensor out of phase, they will usually rattle when hot if that's the issue though ?

[Mr2Mike]

brman said:

I have admit that is what I thought, I have just read people saying it will cause it to go into limp-home mode and always wondered how it would manage to keep and sort of timing at all.

You can have a cam phase sensor fail on some engines and they can still run using batch fired injection instead of sequential injection, but you'd also need a wasted spark ignition which you can't have on a three cylinder engine. If an engine uses a crank sensor for it's primary engine position information then it typically won't run without it.

[mighty kitten]

1.0 vvtii? Micro filter on the vvti solenoid worth cleaning out .

[brman]

S0 What said:

Check the timming chain tension, sometimes it will throw a code up saying cam and crank sensor out of phase, they will usually rattle when hot if that's the issue though ?

It isn't a particularly quiet engine but nothing obvious from the cam chain end so I am assuming it is not this.

Mr2Mike said:

You can have a cam phase sensor fail on some engines and they can still run using batch fired injection instead of sequential injection, but you'd also need a wasted spark ignition which you can't have on a three cylinder engine. If an engine uses a crank sensor for it's primary engine position information then it typically won't run without it.

Thanks, I didn't know that.

mighty kitten said:

1.0 vvtii? Micro filter on the vvti solenoid worth cleaning out .

Yes, 1.0 vvti. I didn't know it had a filter tbh. A good idea given that, when we bought it, every other filter on the car looked like it hadn't been changed in its life. And that was with a full toyota service history
Thinking about it, changing the fuel filter might not be a bad idea either.

I have to admit though, I am getting fed up chasing a problem I don't understand. It is not my favorite car and my wife is also fed up with it so it might be an opportunity to move it on and get something else.......

[Hhman]

I know this is an old thread but thought I would share my experience.
I have a couple of old Yaris 1.0 VVTI's (2002) both have had similar symptoms.
My old OBD could not detect a fault code so upgraded to Torque lite on my phone. Both had similar symptoms. Lumpy idle, low power, difficulty pulling away (even more than normal).
In both cases it turned out to be injector faults. On the second one I had code for injector 1 (P0101 I think from memory) . Moving the injector moved the fault.
Toyota quoted £250+vat for an injector.
£1300+ to replace all 4, with labour. ( I quoted something obscene.)

Got a new injector delivered next day off tinternet for £20. Takes half an hour to fit including tea break.

Both been running sweet as a nut now for over 12 months.
When they get really bad the internal resistance of the injector may prove a definitive test. Compare across the set.