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Old 06-05-2019, 02:31 PM   #1
Drives: Yaris VVTi 2002
Join Date: Oct 2016
Location: UK
Posts: 22
The Intermittent Cranking No Start Yaris VVTi mystery continues. FASTTEC used.

This intermittent Cranking No Start problem has been going on for years in my 2002 Toyota Yaris 1.3 VVTi Auto. It has only about 63,000 miles on the clock and a good service history. The cause of the problem was never identified. You can read up on the history here:

The Yaris has been laid up not working since last year unused. About a month ago it started on the first attempt this year and was running fine. I took it for an MOT and it passed without problems. I was using it every day on short journeys and it started easily. The Yaris was parked up for a week fully working and when I got back to it and tried to start it the old Cranking No Start problem returned.

I have already previously done lots of checks on the Yaris which failed to find the cause of the problem. So I thought a new approach would be more successful. The most comprehensive method of testing I've found is FASTTEC, which is described here:

So I thought I would work through each system below systematically and get your opinions on the results and what to do next. The details are here:

Timing (Ignition / electronic)
Timing (Crank / Cam shaft)

1. Fuel
I don't have a fuel pressure gauge. I had previously checked out the fuel pump which seemed OK. I loosened off the 4 fuel injectors out of the inlet manifold but still connected to the fuel rail and turned over the engine, all the injectors produced a noticeable spray. Removing an injector from the rail produced a noticeable release pressure as fuel jetted out.
I connected an injector wire to an oscilloscope and the injector pulse width was about 33ms over a 0.4 sec cold cranking cycle (cranking speed was about 150 rpm). From what I can see online this may be a bit long and means the car could be running rich (please see photo 1).
I tried disconnecting the injectors and spraying quick start spray into the air inlet but there was no sign of the car starting in this case.

2. Air
It has a new air filter and the MAF sensor was cleaned. The 5 pin MAF sensor has 2 resistors and a ground. The resistors seem to have normal resistance. The 5 pin connector to the ECU had a correct +12V and +5V signal and some grounds.
I removed all the vacuum lines to the inlet manifold and air supply and blocked up the holes.
I replaced the throttle body (complete with a TPS sensor and Idle Control Valve (ICV)) with a known working one- the car still didn't start. I tried starting with no air inlet pipe to the throttle body – still no start

3. Spark
The 4 coil packs were removed and inline spark testers were added. On cranking all 4 sparks testers lit up in sequence. Previously the coil packs were changed and it didn't make any difference.

4. Timing (ignition / electronic)
I connected an oscilloscope to both the Crankshaft and camshaft sensors (please see photo 2) and they both produced cranking signals that seem reasonable. I disconnected the temperature sensor and it still didn't start – I saw some report that if it produces a faulty low temperature reading it can trick the ECU into making the fuel mixture too rich as a cold start situation. I've taken the ECU out and looked inside, it all looks clean with no corroded contacts etc. I've checked and cleaned many earth wires on to the block and fuses.

5. Timing (Crank / Cam shaft / mechanical)
I took the rocker cover off and checked the timing chain by rotating it around with the starter. There was no sign of any excessive wear or damage and the chain seems to get lubricated as the engine is turned over. When the white timing mark on the crankshaft pulley is lined up with the TDC mark then the marks on the camshaft cogs are at the top (after second rotation of the camshafts). This would suggest that the timing chain hasn't jumped any cogs (please see photo 3).

6. Exhaust
The Catalytic convertor was removed and I inspected it internally with an endoscopic camera (please see photo 4). There is no sign of the honeycomb structure breaking up or showing signs of damage. I could see some light coming through the honeycomb at some angles.
I checked the O2 sensors in a gas flame and they produced voltages between about 0 to 0.9V.
The car still didn't start with the exhaust and Cat removed.

7. Compression
The readings from the compression tester were:
Cylinder 1: 7 Bar / 100 psi
Cylinder 2: 2.25 Bar / 35 psi
Cylinder 3: 2 Bar / 25 psi
Cylinder 4: 2.25 Bar / 35 psi
I added a cap full of engine oil to each cylinder and retested the compression:
Cylinder 1: 8.5 Bar / 125 psi
Cylinder 2: 11.25 Bar / 165 psi
Cylinder 3: 10.25 Bar / 155 psi
Cylinder 4: 11 Bar / 160 psi
These reading seem to be more in line with what they should be and I put the spark plugs back in and it started straight away but it cut out after a few seconds. Lots of smoke was produced.
I checked the compression again and the first few compression reading were
Cylinder 1: 5 Bar / 85 psi
Cylinder 2: 2.5 Bar / 35 psi
Having burnt off the oil which was sealing the piston rings or valves, the low compression has returned.

I also noticed that when the engine was turning over but not starting that exhaust gases were venting out of the top of the rocket cover vent hole (with pipe removed). Quite often the cranking revs would increase after about 5 seconds of cranking. Maybe fuel is being burnt but the combustion is not fully contained in the cylinders?
Many people thought that the Cat was blocked as the Yaris was giving a DTC Catalyst System Efficiency Below Threshold error. Since removing the Cat and checking that nothing is breaking up inside, that possibility can be eliminated.

I had considered whether the engine was running rich and even flooding during starting. This could cause low compression if excess petrol washes away the oil seal around the piston rings. I'm guessing that an engine running too rich could cause the Cat error? There are also signs that the top of the engine has got hot in the past as there is sticky baked on oil and carbon deposits under the rocker cover. One idea is if the fuel injectors leak when the car is not used and flood the cylinders. I never noticed any fuel sitting on top of the pistons when I have checked in the past.

Another idea was if the VVT unit was stuck in an advanced position, could this cause the low compression? I heard that the maximum advance is 15%? The VVT solenoid was changed before and it had no effect. The VVT unit uses oil pressure to operate, so if an oil way was blocked or a moving part was stuck in the advanced position, I could see how this could be intermittent. If adding oil to the cylinders restored compression could we eliminate this option?

The only clear fault I have found is the low compression. This is an intermittent problem and sometimes the Yaris works fine and has good compression. This would eliminate worn piston rings. If the valves or piston rings are intermittently stuck by sticky oil deposits, that would have to occur on all cylinders together, could this happen or produce the observed compression problem?

I have another engine ready to swap out if needed, if the problem is not an easy fix.

I would welcome any ideas and comments.
Attached Images
File Type: jpg WP_20190601_20_54_07_Pro (3).jpg (366.0 KB, 48 views)
File Type: jpg WP_20190601_20_41_47_Pro (2).jpg (286.0 KB, 48 views)
File Type: jpg WP_20190530_14_16_57_Pro (4).jpg (233.9 KB, 49 views)

Last edited by YarisVVTi2002; 06-06-2019 at 06:08 AM.
YarisVVTi2002 is offline   Reply With Quote
Old 09-15-2019, 07:42 AM   #2
Drives: YARIS
Join Date: Jun 2017
Posts: 89
did you solve your problem?
rayfloyd170 is offline   Reply With Quote
Old 09-16-2019, 05:43 PM   #3
Drives: 2015 yaris L
Join Date: Jun 2016
Location: Indiana
Posts: 77
The basics are spark and fuel, when you crank it over when it won't start, if it has spark would indicate the electronic stuff is ok, with a plugged exhaust or cat it should start , may run like crap and die, so that leaves something with the fuel. pressure to low to atomize the fuel? water in fuel? injector wires connected to wrong injectors? Looking at the compression test, possibly a blown head gasket in between cylinder #2 and #3?
jra is offline   Reply With Quote

cranking no start, vvt, yaris

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