Misfire, where do i go from here. (Page 12/18)
sanderson231 FEB 28, 11:03 AM

quote
Originally posted by Dukesterpro:

Scanner got in. Fired up win ALDL.

My TPS is reporting 1.2V at a fully closed pedal, which seems a bit high. lol. It looks like I got a bad TPS right out of the box. Gonna to find me a good delco unit.


Does anyone know what good O2 Sensor readings should be. Mine seems to bounce around a lot.



The factory service manual says that the TPS signal will vary from less than 1.25 volts at idle to 4.5 volts at WOT. I'd infer that 1.2 volts at idle is ok.

The O2 sensor should be bouncing around 0.45 volts if the engine is running at stoichiometric air fuel ratio. Look at the integrator reading these should be bouncing around 128 if everything is normal. The integrator is the short term fuel trim and is responding to the O2 sensor. The long term fuel trim (BLM) should also be around 128 if everything is normal. The BLM values are adjusted by the integrator to try to keep the integrator around 128.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

[This message has been edited by sanderson231 (edited 02-28-2023).]

Dukesterpro FEB 28, 11:44 AM
I will have to look into this.

I see on alot of other posts that the TPS should be .5 or .6 volts at idle. My original TPS I believe was in this range


My 02 is bouncing around from as low as 0.018 to 0.480. At work now, I will charge up my laptop and post the log here for you too look at.
Patrick FEB 28, 03:47 PM

quote
Originally posted by Dukesterpro:

I see on alot of other posts that the TPS should be .5 or .6 volts at idle. My original TPS I believe was in this range.



My understanding is that the TPS readings should be around .5v at idle and 4.5v at WOT, although some variability is expected.

I found a post of mine from 12 years ago where I stated... "The idle/WOT voltage readings for my '84 duke are .82v / 4.25v." My '84 ran very well.

What was wrong with your original TPS?

[This message has been edited by Patrick (edited 02-28-2023).]

Dukesterpro FEB 28, 04:50 PM
Cracked housing. Broken plug. It was falling apart. But it was working lol
sanderson231 FEB 28, 05:15 PM

quote
Originally posted by Patrick:

My understanding is that the TPS readings should be around .5v at idle and 4.5v at WOT, although some variability is expected.

I found a post of mine from 12 years ago where I stated... "The idle/WOT voltage readings for my '84 duke are .82v / 4.25v." My '84 ran very well.

What was wrong with your original TPS?




Resistance in the ground circuit from the TPS to the ECM could cause the TPS to read high at idle. Make sure the connections are clean

------------------
formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

Patrick FEB 28, 05:30 PM

quote
Originally posted by sanderson231:

Resistance in the ground circuit from the TPS to the ECM could cause the TPS to read high at idle. Make sure the connections are clean.



Without going through this entire thread again, I've also been wondering if grounds have been addressed. Lack of proper ground(s) can cause all sorts of issues.

Although the following thread is directed at the 2.8, a lot of it certainly applies to the duke.

EVERYONE with a V6 please Read

This post from that thread made me laugh.


quote
Originally posted by JT6666:

After adding the grounding wire, the Fiero was transformed from a stumbling starter to the Magnificent Beast God intended it to be! I also lost 5 pounds, added another inch to the stickshift, and got a smile from the secretary who lives next door. Who knew a piece of wire could make such a difference!


[This message has been edited by Patrick (edited 02-28-2023).]

sanderson231 FEB 28, 11:17 PM
To check if the ECM is properly grounded pull the connectors on the ECM and check the resistance to ground with a multimeter for the following wires:

wire 12 on the white connector
wire 13 on the white connector
wire 15 on the black connector

Looking for resistance of less than 1 ohm.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

Dukesterpro MAR 01, 10:05 AM
I have not checked grounds. Probably a good idea since this engine has been in and out 4 times.


I did notice that BLM stays pretty consistent at 128 when "idling" but as soon as you tap the gas it bumps to 140 and stays there.

Its currently raining, wet and depressing out right now. Hopefully signing a lease on a new shop today. Then I can get to work on the grounds. Will keep everyone posted.
sanderson231 MAR 01, 11:25 AM
Here are the basics of how the fuel injectors are controlled and how the system self tunes. This is for part throttle operation where the system is in closed loop. The fuel injectors are controlled with pulses of 12V. The wider the pulse the more fuel flow. This is known as pulse width modulation (PWM).

There are 16 BLM cells arranged in a grid. Which cell the ECM is in depends on the rpm and MAP (manifold absolute pressure). So at idle the ECM is in a certain BLM cell. As the engine rpm's move up and MAP increases (less vacuum) the ECM moves to a different BLM cell. The BLM value provide for feed forward control. They give a starting point for the fuel injector pulses as the engine moves to different rpm's and MAP.

The O2 sensor provides for feed back control (closed loop). The sensor reads the O2 in exhaust and outputs a voltage signal which goes to the integrator. If the O2 sensor sees a lean condition, the integrator will add fuel injector pulse width and the integrator value will be above 128. If the O2 sensor sees a rich condition the integrator will subtract fuel injector pulse width and the integrator value will be below 128. The longer the O2 sensor voltage deviates from 0.45V the more the integrator will increase or decrease (hence the name integrator).

If the integrator values average 128 the BLM values will not change. If the integrator stays above 128, the BLM value for the BLM cell will slowly increase. Since the BLM is now adding fuel, less fuel addition is need from the integrator. The BLM value will continue to increase until the integrator is averaging 128. So with a BLM value of 140 it means that at that particular rpm and MAP, the integrator has had to bias up the BLM value. This indicates that the something is not as expected and the ECM has had to compensate. It could be a partially plugged fuel injector, low fuel pressure, vacuum leak and other things. As long as the integrator and BLM values stay with their control range (IIRC 108 to 154) the engine will run at stoichiometric air fuel ratio (about 0.5% O2 in the exhaust) while in closed loop. So to get a good picture of what might to causing the ECM to compensate, the ECM needs to be datalogged over a range of operating conditions

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

zkhennings MAR 01, 12:57 PM
Pretty sure the Tach filter is to smooth out the signal going to the tach needle itself so it does not jump around, seems like the other cap is to smooth the signal to the ICM?

When you set timing, did you jump the pins in the OBD connector? Timing will be wrong otherwise.

Can you hook your TPS up to an oscilliscope and make sure it isn't jumping as you rotate it?

Does your dist have any play? Is there play in the shaft? Play in the rotor? Is the spring loaded pin in the distributor cap working properly? Have had that one cause all kinds of issues. Have you checked plug wires to make sure none are arcing?

Check power to the ECU, there are two pins that splice together into one wire that goes all the way to the junction block below C500 on an 85. There is a single pin connector inline at the junction so you can reset the ECU. This line went bad on me and caused all kinds of weird intermittent problems.

Check your C203 for corroded pins, I found a couple there.

Hook up a fuel pressure tester before the TBI, you can rent at Azone, and point a gopro at it while you drive.

To me, backfiring is an indication of timing getting messed up, but it could also be TPS related. A lot of brand new off brand components just don't work right out of the box.