PneumaticTire

I am at absoloute wits end with my 1986 z28 305tpi. PLEASE take time to help me out. First let me tell you what it is doing. It wont idle suddenly. Used to run good until a month or so ago. Now, let me tell you guys what I have done to it lately.

Injecotrs rebuilt by cruzin performance, flow tested and all are at factory specs. New o rings-pintles and caps. There are no vacuum leaks. I'm 100% sure on this.

Rebuilt fuel rail.
New ac delco fpr
new ac delco fuel pump
new maf sensor
new tps set at .54 volts closed, and smoothly operates up to 4.53 volts.
new ac delco iac
New upper and lower intake gaskets, and set at proper torque
new hooker 2055 headers, and 3 in ypipe. !cat
new ac delco plugs
new ac delco wires
new ac delco egr valve
new ac delco egr temp switch
replacement distributor with known good one from a board member
checked timing-at factory spec of 0* TDC. DOES NOT fluctuate at all suggesting a bad timing chain, or anything.
reconditioned wiring harness from tpi parts.net
ALL new ac delco fuel pump, maf power, and maf burnoff relays
new ac delco O2 sensor.

Thats pretty much it on new stuff, so why wont this car still return to normal idle??

Heres what my scanner says. DOES NOT THROW SES LIGHT-Light is working.

Iac position- stays at 145 at 550 rpm. I am the one keeping the engine alive. It fluctuates with higherrpm gradually.

BLM 143? I dont know what this is

Injector pulse width- it stays steady in the 120's when im kepping it alive at 550 rpm, and increases smoothly with throttle increase.

O2 crosscounts, stays at 2

O2 sensor reads steadily rich/lean like i would assume it should. Fast response.

MAF sensor reads a little differnt from what I have read, but it may be my scanner. It reads 1700gr/sec when i keep it alive, flucuating very little, like i would think it should. Increases steadily with rpm.

coolant temp reads correctly at all times with my dash gauge. Never wigs out and says random temps.

EGR acts normal, with 0% duty when Im keeping it alive at 550 rpm, and gradually increases its percentage throughout load.

vehicle goes into closed loop like normal.

ESC counter reads 2 from what I remember evertime I look.

One thing i noticed while timing it, was that my harmonic balancer is wobbling at low rpm. This is definitely wobble, and not dirt tricking my eyes. I never noticed this before and have ordered a replacement from Summit. I don't know if maybe it is making the knock sensor wig out or what.
I have no reason to believe the ECM is bad, but its about what I am down to.

As far as the nuetral safety switch goes, I seen someone somewhere say it can effect idle?? How is this so?? I am down to rediculous stuff like this.

wackytower

I know your in ohio, but where? I have a spare ecm you can borrow if you are close enough. Did you do the minimum air procedure?

PneumaticTire

I'm in Dayton. I hope you are close, lol. I had done the min air procedure in the past, and the car ran fine. It just all the sudden has crapped out like this.

wackytower

Sorry Im in the Cleveland area. Try doing the min. air thing again ive had to do more than once for some reason. Your cross counts not moving is not right and the maf reading way too high for idle. Blm 143 means your extremely lean. I think with everything out whack right there it may be the ecm. Have you have the chip out of the ECM? If so make sure it in all the way and no pins or anything are bent.

jms

iTrader: (1)

If your balancer is wobbling, then more than likely it has slipped and your timing reading is incorrect.

I believe timing is supposed to be 6 degrees before top dead center, not 0.

jms

PneumaticTire

Darn, I used to live near cleveland, lol. Want to sell the ECM?? I did have the prom out but that was when I first got the car, and it ran fine since I put it back in. This over a year ago. I can check again anyway. What exactly is BLM??

"If your balancer is wobbling, then more than likely it has slipped and your timing reading is incorrect.

I believe timing is supposed to be 6 degrees before top dead center, not 0."

As far as the timing goes, you may be onto something now that I think of it.I had a hell of a time finding TDC earlier, I thought it was just me, but everytime I seemed to get the puff of air, and lined up the timing mark on 0, the rotor didn't want to line up with number 1 cylinder. I was just going by what my emission label read under the hood, and setting it to 0 degrees TDC for an auto trans. I could try 6*.

Vader

BLM is Block Learn Memory. It is part of the ECM's learning ability to tailor fuel trims to varying conditions. Here's a little about ECM operation:

GM OBD I System Operation

This generation of engine control systems is a refinement of the first engine control computers and systems. First generation engine controls have some control over spark timing, a few output devices like the EFE system and EGR, and a minor role in fuel mixture adjustment. The OBD I system is designed to control and sense a wider range of functions than the earlier systems, including complete control of fuel delivery, and has proven to be much more reliable and effective.

The system has two basic modes of operation when the engine is running - Open Loop Mode and Closed Loop Mode. In a nutshell, Open Loop mode means the ECM is controlling the engine with essentially no feedback from the engine sensors - the control loop is said to be "open". Closed Loop mode means that the ECM sends control signals to the engine, scans the sensors for feedback to determine further corrections, then adjusts accordingly. The process is continuous, and the control loop is said to be "closed" since the sensors effectively communicate back to the ECM regarding the effectiveness of any adjustments made.


Open Loop Mode

When the starter is engaged, if the coolant temperature indicates less than 100̊F and the intake air temperature is within 20̊F of the coolant temperature, the cold start injector provides a spray of fuel or the cold enrichment subroutine allows longer fuel injector pulses on the service injectors. The cold start or cold enrichment subroutine is of eight seconds duration at a maximum. On a cold-start injector system the extra fuel is distributed to each cylinder via a air distribution system built into the bottom of the intake manifold. If the engine temperature is greater than 100̊F, the cold start injector/subroutine is disabled by the cold start switch or ECM. Upon startup the ECM utilizes information in the PROM to establish the initial pulse rate for the injectors and the engine starts. At this time the engine is operating in Open Loop mode and will continue to do so until the engine warms up sufficiently to enable the oxygen sensor.


Closed Loop Mode

After a warm up period the ECM scans the sensors. If all sensors are operating and within their proper ranges, the ECM will enter Closed Loop operation. This means that the sensors are dynamically controlling the engine fuel and spark. The ECM receives information on intake air flow, coolant temperature, intake air temperature, exhaust gas oxygen content, barometric pressure, manifold pressure or vacuum, air conditioner status, power steering pump load, EGR operation, evaporative canister valve operation, engine RPM, vehicle speed, transmission gear selection, fuel pump status, combustion detonation, and throttle position. This information is used to calculate the proper ignition timing advance and pulse width for the injectors, and fires the injectors for the calculated period. This procedure is repeated continuously in very rapid sequence to maintain the optimum fuel air ratio. The electronic spark control components provide maximum advance, if engine knock is detected the spark is automatically retarded. This too, is a continuous process. It should be noted that the following components are matched for optimum performance - distributor EST module, ESC module, knock sensor and ECM PROM. These components are not interchangeable between 5.0L - 5.7L engines. In the event the information received is higher or lower than the normal range, a code will set in the ECM, and the Check Engine or Service Engine Soon lamp will light.



Block Learn / Integrator

The factory ECM/PCM has a learning capability which allows it to make corrections for minor variations in the fuel system to improve performance and driveability. There are two learning features. The Integrator and Block Learn (INT and BLM) and Block Learn Memory (BLM) cell. The INT and BLM feature is normal with a value of around 128 (the possible range is 0-255). If this value is higher than 128, it indicates that the ECM is adding fuel to the base fuel calculations because the system is running lean. A value lower than 128 indicates that the ECM is taking out fuel because the system is running rich. The integrator is a short term corrective action while the BLM is a long term correction. The BLM value will change if the integrator has seen a condition which lasts for a longer period of time. There are from two to sixteen different cells which the ECM modifies, depending on RPM, airflow or manifold absolute air pressure and other conditions such as AC on or off, etc. The ECM learns how much adjustment is required in each cell, retains it in memory, and applies these adjustments when the engine operates in that cell or RPM/Load Range. These features of the ECM allows the system to adjust itself constantly to your engine and assure peak performance for stock and other than stock engines.

NOTE: When the vehicle power is disconnected for repair or to clear diagnostic codes, the learning process has to begin all over again. To reinitialize the ECM, drive the vehicle at operating temperature with moderate acceleration and idle conditions for at least twenty minutes.

Performance PROMs typically change the parameters for fuel flow, fuel cut-off and spark advance-timing and will allow increased fuel flow and modify the spark advance curves during rapid acceleration. They can be programmed to tolerate differences in idle quality and manifold vacuum due to altered cam profiles and fuel systems.


ALDL Mode

A 10.0K ohm resistor installed between ALDL terminals 'A' and 'B' forces the ECM into Diagnostic Data Request/ALDL Mode. This sends a request for serial data string to be sent from the ECM via the ‘E’ terminal at 160 baud. If handshaking occurs within X seconds or after the first data string is send, the ECM switches to 8192 baud and will remain in the data request/serial data string mode until the ignition is turned off.


Backup Fuel Mode / Factory Test Mode

A 3.9K ohm resistor installed between ALDL terminals 'A' and 'B' forces the ECM into Backup Fuel/Factory test mode. This mode forces the ECM to use predetermined fuel calculations in the ECM PROM instead of the learned inputs in active RAM. This is more commonly referred to as the "Limp Home" mode of operation. Backup fuel is usually around 12:1 or richer from the factory. Once the factory test mode is enabled, it will remain enabled as long as the factory test mode is requested on the diagnostic request input and no system reset occurs.

Note: If ignition is cycled off while in Mode 1 with COP 2 not being toggled, a power down reset will immediately occur).


Field Service Mode

On the OBDI ECMs, you can jump 'A' and 'B' terminals on the ALDL while the engine is running.
WARNING! This must be done after the engine is running. This is called "Field Service Mode" and will not harm the ECM.

If the ECM is in Open-Loop mode, the SES light will flash rapidly, about 2½ times per second. If it's in Closed-Loop mode, it will flash about once per second. When in Closed Loop mode, flashing less than once per second indicates the ECM is enriching the mixture above the 128 count base line. Flashing more than once per second indicates the ECM is leaning the mixture below the 128 base line.


Miscellaneous

An easy way to tell whether the PROM has been installed correctly in the ECM, and contains valid code set, is to watch the SERVICE ENGINE SOON light as you key on. Make sure the ignition is off for at least twenty seconds. Turn the key to the run position without starting the engine and watch the SES light. It should illuminate, then go out, then illuminate again and stay illuminated. This is called a SES light “bounce”. If you do not get a bounce then something is wrong and damage could result. If you try to start/run the engine when a proper SES light bounce is not present, then the computer will default to backup fuel and spark mode because it cannot execute a valid computer program. This can happen if the PROM is in backwards, or not seated, or contains a faulty program, or if the ECM has been damaged electrically.
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BTW - An '86 305 TPI should have 6º BTC base timing if stock. (5.98º, to be precise, but 6 is close enough.)

PneumaticTire

Thanks for all that info Vader. As soon as my new balancer gets here, and I get it on, I'll set the timing to 6 *BTDC. I wonder why my label underhood said 0*??

So if i do the ses bounce test, and it doesnt do what it should, does that pretty much mean my ecm or prom is at fault? Thanks Vader!

1991L98G92

Does your emission label list the fuel system as TBI or EFI? 0 degrees would usually be for TBI engines. Listed in the CATALYST box. Ex: EFI(TBI) AIR O2 ORC

PneumaticTire

dont know for sure on that.

My SES light does do the bounce test like it should.

RednGold86Z

iTrader: (1)

Sounds like your IAC is fubar (even though it's new). 145 counts at 550RPM means the computer has told it to open, but it didn't open. There's no feedback on the IAC motor itself, so the computer doesn't know if it opened, other than it sees the RPM go up.

Maybe it's got some bad wires to it. Maybe there's a problem with the computer.

PneumaticTire

I was unsure on the IAC specs as far as what it should be doing exactly on a scanner. You may be onto something here. I have been thinking of looking into the iac again myself conincidentally. I doubt my wires are bad, since the harness was reconditioned and all new connectors put on, but I'll check for proper voltage anyway. At this point, I am open to all suggestions.

Thank you all so far for the info. Keep it coming!

wanosdia~s

My

wanosdia~s

mt buddy currently purchased a 85 camaro w/ a tpi engine and the previous owner said that it had an engine swap but wasn'tr sure of what year or what cubic in. the motor is and from the looks of it the wiring harness needs some reconditioning ,I need help I'm new to all this fuel injection stuff but I'm eager to learn please send any info possible it would be appreciated.
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void this post new to this stuff