ECU problem??? or something else?

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hrforever

Member
Messages
196
Location
Melbourne, Australia
I have previously outlined my problems earlier under the title 'Loss of low speed smoothness' but I feel its gone beyond this.

Background info, conversion using 95 SC400 motor, Supra W58, with uncut wiring and standard ECU. Run well for 18 months without problem. Has always had codes 27, 29 and 42 as none of these sensors are installed. Because I have been unable to make sense of whats happening I've had my mechanic look at it but he also is stumped.

Problem, when parked the car idles as normal and revs out without complaint. When driven, there's no response from the motor unless you can get it above 2500rpm, then there's instant, neck snapping power. Below the 2500rpm, driving is difficult, with a feeling the cars power is being retarded and you cannot accelerate.

What I cannot understand is that this problem can be temporarily fixed by disconnecting the battery, giving you a 5km break from the madness. Cold start, hot start, short drive, long drive, it makes no difference. Once the problem returns it won't go away and there's no error codes to point to the problem. Does this suggest its the ECU? I've checked all wires and connections as well as inside the ECU but cannot see anything out of place or 'burnt' and I've been unable to locate a replacement to swap in to test.

Is there something I've missed or can try to narrow this problem down, as my limited knowledge on this has been exhausted. I am open to any and all suggestions or offers to get to the bottom of this.
 

Zuffen

Super Moderator
Staff member
Messages
5,477
Location
Sydney, Australia
I'm not into the codes as I don't use a Toyota ECU on mine.

What do the codes tell you and what sensors don't you run?
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
The codes are for the two sub oxy sensors and the speed sensor. But these have no effect on the cars operation. This problem is from the last month or so and at its worst makes the car undriveable and dangerous.

I am only assuming its the ECU as the problem can be overcome by disconnecting the battery whereas if it was a temp, air flow, crank angle, cam or throttle position sensor the problem would always be there or a code would appear.

How do I proceed without loosing more hair!
 

cribbj

"Supra" Moderator
Staff member
Messages
4,794
Location
Houston, TX
Start looking for more clues - go back to basics like:

1) Do you have good fuel pressure?

2) Good battery voltage?

3) Good spark?

4) What do the plugs look like?

5) Start wiggling some of the wires that you changed and see if it affects the problem.

Swaps are always devilish to troubleshoot because there are so many more possibilities. Owners modify harnesses & connections and usually don't do as good a job as Toyota did, and things start going flaky down the road.....
 

JBrady

Active Member
Messages
1,776
Location
Houston Texas
Very strange. Sounds almost like limp mode. Almost worth finding an ECU from a wrecking yard to test against. Worst case you will have a back up or you can sell the ECU on ebay if it is not your problem.
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
Strange doesn't cover the half of it. A replacement ECU is rarer than hen's teeth from my searching as its a 1995 model. Plenty for earlier years can be found but their not interchangeable.

All the basic have been covered by me and the mechanic so we cannot progress with a clear idea of what we're looking for. Is it possible to have the ECU checked and if so where.
 

Sudsy

Member
Messages
161
Location
Sth Oz
There is a bloke in Melb that does ECU's but cant remember his name. I'm sure there will be someone on here that will know who i am refering to. I think he is mentioned in one of the other forums
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
In order to fully and completely get to the bottom of this, I believe it is necessary to test each sensor individually whilst the car is running with the problem. Thing like TPS, AFM, O2 sensors, etc. I know they are not throwing up codes and the ECU can run properly after the battery is disconnected but I cannot proceed without testing these and fully discounting them.

So, how do I test them and what am I looking for? Is there a base setting or reading for each sensor? Replacing each sensor or the ECU with a known working one is not feasible as I don't know of any other 1995 1UZ I can raid for parts. so further testing is all I have left.

Can anyone tell me what I'm looking for?
 

Zuffen

Super Moderator
Staff member
Messages
5,477
Location
Sydney, Australia
I think you will find all sensors are interchangable.

The ECU may be unique to your year model but only by check the part number on the ECU will you know.

I agree with both Johns, the vehicle does sound like its in limp mode and I wouldn't suspectthe engine or ECU I would suspect the intergration into your vehicle.

I think the gent in Melbourne is Harry Lemmens (not sure of the correct spelling). Try searching his name on Planet Soarer as I know he used tog et mentions over there. Haven't been there for some years but he should show up.

Another search would be "speed limiter removal" as he was modifying ECU's at one stage.
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
Ok, still poking around. Cleared all codes and went for a drive with the AFM disconnected, I can get almost the same crap drivability as when the problem occurs by itself. Before the mechanic cleaned it this was not the case as it would drive fine but not rev out.

So the question is, does anyone have a spare AFM (model 22250-50060, looks like black plastic tube with with connector plug) that I could try or failing this will an alternative unit suffice?
 

converted

New Member
Messages
104
Location
Sydney
i had very similar issue to this on my boat a few weeks ago. turned out to be a coil . pick up a good secondhand unit and try swapping one at a time. also the coil didnt present itself instantly it gradually went off. It was like i had sour or dirty or water in the fuel to start with, engine was getting sluggish, throughout the day then it just would not develop power from idle to 2500 (sounded like a sick twin cam 4cyl engine). If i could get over 2500 it kicked in.
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
More research done. It appears that fuel may be the problem so I'm looking for confirmation that the fuel pump is operating properly before I next check the injectors.

At idle fuel pressure is 60psi
At wide open throttle pressure goes to 75psi
With the return line pinched pressure goes to 90psi

Thing is, when holding a constant 2500rpm in neutral the motor does not sound happy, but pinching return line the motor revs a lot happier.

The pump is wired direct to the battery, not through the ECU so it always runs at 12v. Do the above pressures sound right????????
 

Zuffen

Super Moderator
Staff member
Messages
5,477
Location
Sydney, Australia
If the engine is standard it should run 43psi.

The only reason a naturally aspirated 1UZ should ever go above that is if you're below sea level.

Pinching the return line and having it rev better is the opposite to what we would expect. I would think the engine is runing rich, as the increased fuel pressure will increase the amount of fuel the injectors will pass, so pinching the line and increasing the pressure should make it run richer.
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
Zuffen, my readings are of the fuel pump pressure before the fuel rail so the regulator should reduce things, and given the change in readings I am assuming the regulator is working. If pinching the return line makes it run better, that suggests that the increased pressure in the fuel rail is also increasing the flow through the injectors therefore making it run richer and suggesting the injectors are not flowing properly at the normal regulated 43psi.

Make sense???? or could I be barking up the wrong tree.

PS. Replaceing the coils did not change things
 

Zuffen

Super Moderator
Staff member
Messages
5,477
Location
Sydney, Australia
Thinking about your post partially blocked injectors sound a fair chance.

It's quite common to have blocked/stuck injectors after an engine sits for some months/years after it was last used.
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
Had them cleaned today but they appeared to be ok on initial test. Will refit tomorrow so if this doesn't fix it next on the list are the 02 sensors, even though their not throwing up any codes. They have been replaced with universal 4 wire units so perhaps the ECU is not communicating with them properly.
 

sideshow

Active Member
Messages
2,404
Location
Qld
75 psi fuel pressure is definetely wrong

either stuffed gauge or u have a blockage somewhere
neslry double fuel press will definetely run rich
does it blow black smoke

fuel press should be 38 to 42ish anywhere along the hi press line from pump outlet to fuel rail

the reg will hold it at around 40 ish anything else then u have blockage in return line
or stuffed reg
if its factory reg remove the return line off reg and let fuel run out into can or bucket
then recheck if press is to hi check with another gauge
if still too hi then replace reg
i would fix press prob before looking at injectors
 

hrforever

Member
Messages
196
Location
Melbourne, Australia
Thanks for the response Sideshow. Do any other Toyota's have a similar reg? Specific 1UZFE parts are a pain to find locally. As for the gauge, its from a neighbouring carby shop so I would expect it to be reasonably accurate. As for black smoke, non has ever been evident. Will check reg and return line tomorrow.
 

sideshow

Active Member
Messages
2,404
Location
Qld
most regs are similar but the plumbing might be different
so as there is no room in back of a 1uz then i doubt many other regs would fit

ive never seen a reg play up in over 1000 wiring jobs
not that they cant fail but just seams weird to have 75 psi
something must have happened or something got changed
of maybe dirty fuel but even then at 75 psi that would push the gunk thru to tank

but if it runs good when u disconnect battery then it cant be fuel pressure
i think even if u disconnect o2s it should still run ok if it was ok before so i would not worry bout o2s at this moment

have u looked inside ecu for bad capacitors or corrosion
 
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