How to scope Air Flow sensor with Picoscope 2205A

Hi, I am still on a battle with the 3VZE engine and perhaps if I can get a good trace on the scope I may find the problem
Specifically would like to get some help on what ECU terminals use to hook up the scope and an idea of what to expect from Air Flow Sensor and TPS .

My thought was IF it shows that it has some jitterbugging on the voltage reported to the ECU then I should that the sensor apart or just replace, Both should in my opinion give a smooth curve representing the volume of Air entering the manifold and the percentage of aperture of the butterfly for the Throttle. I am not proud of the diagnostics but not a full time mechanic learning to use the PicoScope 2205A

Any pointers on the subject appreciated.

Please refer to the attached drawings for the 1995 A/T, 2 Wheel Drive 3VZE engine 6 Cyl.

The engine runs very crappy and missing from 1300 to 2000 RPM
Fuel Pump remains on at 40 psi;
Timing Belt 5 years and rechecked perfect
New HV wires and distributor
New coil
New injectors
ECU was swapped 5 months ago, then quit. Try 2 used ones from eBay and does not run at all. but runs badly with original. Sometimes runs very smooth at 3000 RPM. After a while sometimes engine quits but starts quickly

 

Is the check engine light illuminated?
What is the fuel pressure at the fuel rail at varous RPM's?
How is the condition of the air pipe between the AFM and the TB.
Are the ground wires in good condition?
Get a DVM and probe the wire harness for opens and/or shorts.

 

I do not have engine light.
Fuel pressure without regulator 44 psi and 39 with it and steady weather running or stop. no leak of pressure unless more that 100r 15 hours.
AFM in bad shape in my opinionbut seems to work. Checked wire to ECU and seem OK
Some grounds werenot good so I run ground cables everywhere I could think of.
I checked as many wores as I could (AFM & TPS & Distributor) all seem good, but I get a lusy scope of Distrinutor NE, G1 and G2
Thanks

 

Also a friend help me to find air intake leaks and corrected many. Now hard to start some times even with good fuel pressure (gauge connected semi-permanent)
How should find out of injectors (are new) or wire to injectors or connectors are ok without removing intake manifold?
What would be a good plan if I do that? The scope reading at #10 and # 20 ECM look good, but do they reach the injeectors?How to check?

 

You can get to the DS injectors with a long screw driver or perhaps a diagnostic stethoscope if you have one. PS injectors are not so easy! The clicking is very apparent so if one or more are not triggering you will know quickly as you can hear them. However, they may be clicking just fine but the screen inside could be clogged and little to no fuel is being passed into the cylinder.

The distributor has the dual purpose of distributing the high voltage to the spark plugs but also acts as the crank triggering mechanism for the ECM to gain knowledge of the cranks position. My original distributor finally quit as the sensing coil/s finally died and it was getting harder to start as this neared failure. Once the signal coil had failed the check engine light was illuminated and a DVM diagnosed it fairly quickly. So you may have the same thing going on.

The temperature sensor that the ECM uses to tell it how hot the motor is has a key piece in getting things right for cold to hot starting and general running of the engine. It is on the rear manifold with all the other thermal switchers and sensors. If yours is original looking you might consider replacing.

The harmonic balance-pully is rubber isolated from its hub and can fail or drift when they are old. My truck seems to run really well with the static timing at 14° BTDC with the jumper in place to set it. But you need a timing light to get this adjusted.

 

I had put an eBay NKG O2 sensor into my exhaust system after my engine rebuild thinking the OEM Denso was done-for. But every time the engine went closed loop as it warmed up it would run like crap and not respond to accelerator input. I finally put the Denso back in out of desperation in trying to not ruin a brand new CARB complaint CAT that was sulfuring when I ran the engine. It was getting over loaded with too much fuel and it was over heating. I also put spring clamps on most all of my vacuum lines and poked wire down and blasted compressed air through all of the metal lines that make up the vacuum plumbing on the plenum. The diaphragm that is on the fuel rail is a pressure relief valve and it was not getting any vacuum signal because the metal line was plugged up with rusty crap and was blocked and that was part of the over fueling problem. Too much fuel pressure is not good as I realized by putting a pressure gauge on the fuel rail. The injectors need a fairly tightly controlled pressure range which is why there is a damper at the inlet to the fuel rail and relief valve at the opposite corner near the oil cap.

• What is that temperature sensor doing and is it original? It controls the ECM from going open to closed loop once the motor is warmed up. It also might have an air bubble under it's sensor head. That rear manifold can be hard to get free of air and I took out my sensor and let coolant flow out to be sure when I replaced it.
• Cracks in the large intake air pipe/s to the throttle body: are you sure the air pipes are sound and not leaking because that will toss the AFM flapper to a disjointed position and will not jive with the TPS and the relative throttle plate angle thus confusing the ECM as the RPM is increasing. The AFM is real piece of work and is not like a MAF in many regards.
• You might ping YotaTech for more info if your diagnosis is still dead ended.
• A look at the spark plugs might be prudent too.
• Also a lot of new stuff doesn't means its good as in DOA or infant mortality as there is a ton of crap Chinese stuff out there which you might have as some of the new parts? I'm on my second O'Reilly distributor as the first one's distributor cap cracked after a month. Oh was that ever a surprise when I had the lights off and could see the high voltage light show.
• The other thing to look at is the knock sensor it can give the ECM fits if it is not working when in closed loop and the single wire has a rather ugly path in getting to the connector plug on the wire loom. The Toyota OEM part is the only thing that works from what I have read and is also $$.
• At WOT and during acceleration the manifold vacuum drops off but the second you let your foot off the pedal the throttle plate is damped to a slightly closed position as the dash-pot keeps the throttle plate slightly open as it bleeds off the air from its diaphragm though a small hole. As this is happening the manifold vacuum increases and the pressure relief valve on the fuel rail opens and reduces the pressure in the fuel rail. It is a very intricate dance of pneumatic's, hydraulics, mechanics, and electronics in keeping the emissions as low as possible for this OBD I monster such that it is and to keep it from back firing and killing the CAT! At this juncture in time the dash pots diaphragm is probably rock hard and has no more compliance and cannot slow down the closure of the throttle plate the way Toyota had engineered it to do. Its not cheap @ $75.
• Have you checked the diaphragm that is the vacuum modulator for the EGR. There is a plastic cap that is snapped on and off and it has a fabric filter inside it. If the port has turned the filter black were the port is opposite then the diaphragm is wasted and you need a new part. You can use the ones for other Toyota models it will just be missing a lug that orients it in the spring clip at the proper orientation. But the vacuum lines will manage that need.

This vehicles 3VZ-E will challenge your very understanding for every mechanical discipline there is in figuring out what is wrong with it. But when its fixed there is nothing more rewarding than hearing that 3.0 L V-6 sing!...