Elvota

I know I am missing something (a lot of somethings) but I can't understand what the ECM (computer) can or does do to effect the engines performance, even with the multitude of sensors telling the ECM what is going on.

Everything seems physically connected. The crankshaft connects to the camshafts via timing belt. Distributor connects directly to DS cam shaft via gear. Rotor spins in cap via this connection, sending spark down the line every time they connect.

How can the computer change any of this? Spark duration? Fuel injector pulse... but is that all that can be changed electronically once the motor is turning?

I realize there is much more to the process, and I am new at all this. Just trying to better understand how the ECM can help, and hurt, engine performance. My 3.0 runs well, but just seems a little off and I am trying to understand the sytem a bit better.

Thanks

dcg9381

How can a carb impact performance? The EFI is your carb.. It essentially regulates fuel. The air is still a physical process, but the EFI determines how much fuel you get and how often. It attempts to regulate the right amount of fuel given an amount of air, but it has it's limitations.


What about spark? The EFI determines when you get a spark - and how advanced or retared the ignition system is.

TNRabbit

The ECU (Electronic Control Unit) changes the fuel delivery and regulates the spark advance/retard according to conditions (octane of fuel, air density/temperature, engine temperature, etc.). It also uses the VAFM/MAF to determine air/fuel ratio.

What exactly is "off" on your 3.0 (details please!)? I just finished a major tune-up; maybe I can offer some suggestions...

Elvota

Maybe my question is more about the distributor and timing then.

If rotor spins mechanically in the cap, doesn't a spark fire every time the rotor hits a contact? Does the ECU change how strong or long the spark is? What does the ECU have the power to change that effects the timing?

Basically, my truck runs well, but seems to lack power and torque. I know, 3.0 is sleepy.

Thing is, sometimes I have reasonable power, and sometimes I have very little. There doesn't seem to be a real pattern, hot, cold, altitude, etc. I can just feel it giving up sometimes, like trying to start in 3rd gear or something, and then other times the motor pulls just fine.

One thing I do know, with timing light on #1, and TE1 to E1 jumped, my timing mark is irratic (unjumped it's still irratic). Jumps 2 degrees or more, will never settle. I try to set timing at around 10, 12 degrees, but impossible to be accurate.

Some have suggested loose timing belt (which is 5000 miles new) which makes sense somewhat. All this leads to my rather simple question about what the ECU does. My theory is the ECU is fighting something, trying to help me out, but screwing me instead.

I don't seem to have any related codes.

Basically, I am trying to figure out if the problem I have is mechanical or electronic. I know it could be a lot of things, but without breaking out the list, I have already done almost everything yet this bouncy timing still escapes me.

Thanks in advance for any further ideas, info.

MRunner

Does your engine idle smoothly in an out of gear? Cold and at operating temp?

Under load (say going up a hill) and under 3k RPM, does it jerk or surge?

Whats your average MPG?

Bumpin' Yota

your timing should be rock steady not varying all over the place. Make sure the AC is off when you do yourtiming check. When the clutch engages it idles up the motor slightly thus advancing the timing

Bumpin' Yota

Everyone covered pretty well what the ECU does....it changes the spark/ignition timing by tripping the coil sooner or later pending conditions. It controls fuel amounts by increasing or decreasing injector duty cycle.

dcg9381

Here's a write up on it:
http://www.autoshop101.com/forms/h59.pdf

The ECM triggers a spark at an appropriate time. If it didn't the coil would arc all the time, even when the rotor was inbetween terminals.

ECM doesn't determine how "strong" the spark is. Spark is either triggered or it's not.

The ECM can delay the spark, say under detonation, even though the dizzy rotor is positioned correctly.. The rotor is on the terminal for a long range of engine timing. When going to an aftermarket ECU part of the challenge with the dizzy is to make sure you're setup to trigger only when the rotor is pointing to a terminal.

Elvota

Thanks for all the information.



Answers to some of the posted questions.

1. Idles very smooth. It's a manual, so in gear probably doesn't matter, but smooth regardless of in or out of gear.

2. AC is not on when checking timing. AC not currently connected.

3. MPG probably won't be a tell at this point (35" tires, SAS), but I get around 15 to 17 depending.

4. I get no jerking or surging under load, hill or otherwise. The only thing I feel is a sense of nothing. Just very little torque, like trying to run a gear high, shifting to soon... like the engine can't catch up.

I got a TPS and a distributor off a good shape similiar year vehicle. I may swap to see if one of these makes the timing steady.

Of note, I don't seem to get a change in timing when I jump TE1 and E1, even though it is hard to tell with the marks wandering. I have read that no change once jumped can indicate the TPS is out of adjustment or bad.

I'll post what I learn. Any further ideas/ suggestions welcomed.

TNRabbit

Sounds like TPS; however, with 35" tires, what gear combo are you running? If stock, that will explain why you have no power!

MRunner

What can cause unsteady base ignition timing? When I set mine to spec (10 BTDC), it will be at 10 but jump up up to 13-15 then back down to 10, then back up, etc. Has new TPS, properly adjusted.

rdharper

In terms of useful theory, the Wikipedia is becoming ever more useful. Here are two links.

For some history: http://en.wikipedia.org/wiki/Engine_Control_Unit

And another link specific to Toyota (also from the Wikipedia): http://www.autoshop101.com/autoshop15.html

For instance, checkout number 33 on Position Sensors, including the TPS.

Elvota

Thanks again for all the help and links.

I think I may have figured my problem out today.

After messing with the TPS forever and really seeing no change, I decided to try and swap in another distributor body I had pulled from the salvage yard. Low and behold, timing finally stayed still!!

Was able to set to 12 degrees and truck seems to run very well now. Marginal power increase, but much more consistant, which was my main concern at this point in time. The only thing that isn't "perfect" is the idle does not seem to drop when TE1 and E1 are jumped... so I may mess with the TPS a bit more depending on the results I see.

After looking at the old distributor, it seemed to spin very, very freely comapred to the newer one. Guessing here, but think perhaps this loose feel was contributing to the jumpy timing. It could of course be something else in the distributor entirely, but either way I seem to be on the right track with the new unit.

Only 20 miles so far, so I guess time will tell. I'll post again if something changes in an effort to help others with similiar issues.

Oh, and I run 5.29 gears, so this is as strong as the 3.0 is going to get with my set up, which isn't half bad once all is said and done.