WHat would be a good a good approach to diagnose Lack of power under following:

Vehicle: 1995 4Runner 3VZ-E engine
Complaint: Lack of power for this 6 cylinder engine with good compression

Looking for HELP on a better diagnostic procedure

What has been done:

- Replaced wires and plugs that were in sad shape
-Replaced Alternator that was not keeping the two years old battery charged
-Checked cylinders compression: from 157 psi to 159 psi
-Checked Timing Belt and timing set up and found in good conditions and as replaced 6 years ago. All marks spot on.
Checked engine vacuum idling and snap throttle and comes back right on to 15-17"
-Replaced Ign Coil with new one. (Improved a little)
-Replaced distributor with a new one even the old one was seemingly providing good wave forms on scope at the bench and all ohms were OK. (Improved a lot more).
-Checked as many grounds as possible and run new ones to ensure good ground to sensors and ECU.
-Replaced igniter with used one (no changes)
-Checked Fuel pressure with gage and OK
-Replaced all injectors with new ones (Improved a little)
-Replaced TPS with new one
-Replaced ECU with a used one (More improvements, but still no enough power
-Rechecked Ignition timing 10 degrees BTDC with paper clip on


Codes Originally after the 1st. complaint
. - No EN signal from distributor to ECU.-Checked cables and distributor and OK.
. Intake air Temperature (Run ground wire to sensor and code did not appeared any more)
. Code 25 , air-fuel ratio malfunction
. Code 14, no IGF signal to ECU
. Code 41, Short on TPS


No codes as of today after extensive test run, but still lack of power. Engine can hardly get the car to 60 miles/hour

The intake manifold needs to be taken off to get wave form from injectors with car running. So maybe should I measure with the CC-650 amp clamp at the ECU? This is OBD1 and do not have scanner to view data.

Any ideas ? I have the FSM from Toyota in 1995 and I can try sensors or other parts with the Picoscope 2205A and HV clamps and attenuators.

Getting close to the point of giving up and throwing the towel, seems more than I can chew.
I am replacing Fuel Filter tomorrow and if no changes time to find someone with good diagnostic equipment and experience.

I easily will win the First Price on a "Parts Changer" contest. Not very PROUND OF IT !!!

MAF sensor... inspect and clean to start with...

What are the fuel trims telling you??

couple things:

too much exhaust back pressure, ( faulty cat. ) did you check exhaust back pressure before the converter, ( check at pre 02 sensor bung, sensor removed of course )??

you said you check fuel pressure, but what about fuel flow?? is it within spec??

mechanical drag on the chassis, ei... brakes dragging, alignment off, transmission/diff binding.

do all the wheel spin very freely with little drag??

Thank you scanerjohn for you suggestion. Now this Toyota 4Runner 1995 3VZ-E engine has an Air Flow Sensor instead of the MAF that I was more familiar with.

In addition this is OBD-1 and I have no data Scanner to watch Data. I have SnapOn "brick" 2500 and purchased cable adapter for OBD-1 to OBD-2 and it fits with both connectors but does not connect at all. Someone in the YotTech Forum told me that there was zero chances of see something since all data scanners had different protocols and recognized only what they were built for.

I can only access points for data on injection at ECU, but I am afraid to get into wrong points and burn the ECU with the PicoScaner 2205A since no other source to utilize.
The 1990-1995 FSM does not have any info on where and how to watch sensor with the Oscilloscope. Also I am battling with my ignorance since I just got into the Scanner utilization for diagnostics.

I will try today to scope at the ECU the voltage waveforms for the Right and left injectors. Also the voltage variations of the Air Flow Sensor which some people in a forum suggest they go lean with age (This car 25 years) and could be adjusted.
Thanks for you input.

As I answered above to scanerjohn I do not have capability to read data for OBD-1 and as a DIY working for free, just for pleasure on a neighbors' car do not justify buying OBD-1 equipment since it phased out.

If I get some impulse I will try to Picoscan the O2 analyzers' behavior and also the Airflow Sensor since this engine does not have MAF.


Any ideas on how to Picoscope these two will be very welcome.

Thanks tech25 for your suggestions. I will check for drag but judging by the fact the car rolls freely on a driveway with little slope makes me think is not a problem. But I will check.
Now it is funny that the car I changed the ECU yesterday (used one) and it seems to run well, today's test run show the brake light coming on anf of intermittently with no reason at all from the parking or brakes at all, and no different feeling on the drag of the car on downhills or leveled terrain.

As for back pressure I do not know how to measure that except with the vacuum gage on and a snap throttle watching for slow return on the vacuum side. It seems normal with that.
Should I do something different? I do not have a low pressure adapter for my PicoScope 2205A. I have seen people building one with Vacuum Tank sensors.
Should I do that or any other way to check?

Forgot about the Fuel Flow. The only thing I did was watch a pressure gage I connected to the rail and a couple Long Snap Throttles to see if pressure went down at all. it did not.
Any other way to do it? May if I can figure out how to get a Picoscope waveform from O2 sensors? I will try that this afternoon.
Thanks

I cannot find any specs for fuel flow, so sorry about that, cant be certain about that.

if you go to pin 4 in the data link connector in the engine compartment, it should be a black wire.. that appears to be
the signal wire coming from the a/f sensor/o2 sensor.

I would definitely hook up the pico scope, and select the predetermined settings

here is a example...

I went to the 17-18 Data Link Connector on the engine compartment and read the O2 sensors waveform to ground. This is what got and cannot make much sense of all those spikes that do not at all the waveforms I found for sensors that work on the 0.2 to 0.9 Volts.
But the spikes seems to be controlling the fuel mix since the car is running better now after I swap the ECU with a used one.

Also I could not figure out how to adjust the kickdown so when the gas pedal is depress hard and the car do not have the power in Drive, kicks down to second gear.
I try with the cable near the accelerator shortening end extended but not results.
Any help appreciated.
I am trying to attach three files I saved from Pico of the two O2 sensors

In the OBD1 days on the few vehicles that did not give scan tool data I would hook wires up backprobing the ecm.
Watch the O2 while driving see if it goes biased.
Watch and graph the mass arflow and see if it dips or drops off or is out of spec.
What does your vacuum guage show while driving down the road.
If you have a plugged exhaust you will tend to lose power and vaccum will drop off on a vehicle that is plugged or partially plugged or plugs when driving.
If plugged it Will drop off to below 10 it should be near normal maybe 15 when driving.
and if doing your idle snaps it should come back quickly, not slowly.
You could try a back pressure test if it is plugged you will see more than .5 psi
when revving up and holding to 2000 rpm. If its plugged you will see a psi or several psi.
I have used the vacuum guage and sharpened a point on a piece of brake tubing.
poked or drilled a small hole in the exhaust before the cat (you can close it with a self tapping bolt). But a word of caution if it is plugged badly it will will peg the
needle on vacuum, pressure guage and wreck its accuracy.
A map sensor like a GM (89-2000) vehicle one works well for a vac transducer give it a supply with a 9v battery.

Basing my opinion on the vacuum gauge reading you posted.

It’s low engine vacuum but 17 inHg isn’t uncommon on older worn out engines. But 15inHg makes me think you need to either advance your distributor, or your looking at a volumetric efficiency problem. likely a plugged exhaust as others have mentioned. You can remove the upstream 02 from the bunghole and see if it has more power. If it does... well does someone really invest in putting a cat a 20+ year old vehicle? And what killed the first one?