Is this a misquote?
The car should go into closed-loop once it's warm and everything is functioning properly-
If you are in open-loop, the computer isn't running off the O2 sensor and will rely on the tables in the tune, which most likely are set rich. I can totally see why it's running rough if this is the case.

 

check coolant temp sensors one for the guage and one for the ecm, also check the ect signal at the ecm. It would be good to check with a analog meter from cold to hot to watch for dropouts. While you have this meter out check for dropouts of the tps. Good luck!

 

Hal1991

Lots of good advice in this post

I went through a very similar time with my C4 Vert. I installed a GM ZZ4 Fast Burn crate engine with a hot cam. along with was a new Doug Nash 4 speed trans,, new Dana 44 @ 3:73, new S/S exhaust, without the short Cats close the the heads, and a few other small components.

I used the stock tuned port 100% and stock PCM with all new sensors and resealed t-body.

The engine ran like, well Crap. So I called a fellow Engineer (that was a design engineer at the time) at GM Corvette design center. In simple words He laughed...

He instructions were to

test all of the Vbat (+12 Volts) on all of the engine sensors,, lucky all good, none damaged

test and inspect all PCM harness grounds,,,, I found several frayed and one not grounded

Install larger injectors (forgot the size), and label the wiring harness connectors prior to swap.

Install 4 wires Oxy Sensors

Install larger Throttle body...

This solved nearly all of my engine issues. But, the engine would run great and then crappy. After dinking around I for some odd reason removed the BBK top cover plate on the throttle body.

Turns out there are air passages under this plate, new gasket, getting better.

Now that I actually got the engine to mostly run, we went into the prom burn cycle. The forth burn was pretty darn good and is still installed

Then I installed a vac canister (stab vac) and then went through the never ends routine of plug gap and timing, the timing was the miserable part.

Oh, also had to change the fuel regulator for an adjustable unit

BUT, I still don't particularity care for the GM OEM PCM and wiring harness. So, I'm thinking it might be time for a swap sooon. I'm leaning towards Miniram or RamJet

BUT, one frayed wire on a ground or a ground in the incorrect location can drive you nuts chasing these issues. I do recommend at this point to check every sensors Vbat and sensor Voltage to be able to cross it off the list. You can check the sensor Volt levels with a good scanner.

When a EFI, Electronic Fuel Injection PCM system, when the Engine has been operating for the specific time period and the engine is at operational coolant temperature, the PCM places the engine in "CLOSE LOOP",,ie all engine sensors are in full operation and the combination of all of them determines engine operation, FUEL RATIO and etc...\\
\

So, if your engine goes to over rich condition or any other change when going into Closed Loop, You have a Sensor to PCM issue !!

Very unlike it will be as a result of fuel pressure, cats, plug gap, fuel, timing etc. It most certainly is in the EFI someplace.

List out all of your engine sensors values. And then get the engine into closed loop and compare all of them,, one at a time

BTW, if you have an EGR valve on this engine, remove it and check it per test procedures. a defective or sticky EGR can cause very erratic operation.

Lastly, my S-10 2WD pickup went through dizzy ignition modules every few months. Ran like crap, but no excessive fuel rich issues. I wouldn't assume any electronic component to be operating properly, even now parts,, check them all.

Could you have a defective Miniram PCM or wiring harness ??, yes, but rob very unlikely.

You may have more than one issue with your new engine swap ??

GOOD LUCK

 

The only additional sensor involved in closed loop mode is the O2 sensor. It needs to be HOT to work, so it takes a while to get up to the proper temperature. Sometimes it never gets there, which is why heated O2 sensors are sometimes needed.

 

here are few of the tables saved in GM PCM's. these are calculated via various sensors

Closed Loop
These parameters influence the VCM’s Closed Loop Fuelling behavior.

Closed Loop Enable ECT vs. IAT: This table sets the coolant temperature required to enable Closed Loop in relation to inlet air temperature (IAT).
Closed Loop Enable Coolant Temp vs. Startup Coolant Temp: This table sets the coolant temperature required to enable Closed Loop in relation to startup coolant temperature.
Closed Loop Enable Delay: This table sets the delay (secs) after startup and before closed loop will be enabled.
Closed Loop ECT: This is the Engine Coolant Temperature (ECT) above which closed loop will be enabled.
O2 Readiness ECT: This is the Engine Coolant Temperature (ECT) above which the O2 readiness tests will be enabled. On some vehicles once the O2 Readiness tests complete successfully the PCM will enter Open loop STFT mode ie. enabling the STFT's even thought he closed loop enable temperature has not been reached.
O2 Readiness ECT vs. Startup Coolant Temp: Below this coolant temp the O2 readiness tests will not run.
Closed Loop Mode vs. Airflow: This table defines the Airflow mode the Closed Loop routines use to operate. It controls selection of various gains and delays used to interpret the O2 sensor signals.
These tables define the Rich/Lean switching voltages for the O2 sensor in relation to Airflow Mode.

O2 Sensor B1 R/L vs. Airflow Mode: Table for Bank 1 (Driver Side)
O2 Sensor B2 R/L vs. Airflow Mode: Table for Bank 2 (Passenger Side)

These two tables affect the % fuel needed for proper closed loop response and start the STFT process

Closed Loop Proportional Base vs. Airflow Mode: This table returns the base proportional % fuel change. Proportional base rate table is the primary amount of fuel needed to drive the closed loop fuel control into oscillation. Proportional fuel acts like an on/off switch to keep the fuel moving around the current O2 Rich/Lean vs. Mode table set point. The values on the Proportional Table add or subtract to the base fuel rate depending on the previous fuel condition (i.e. if rich then switch lean, if lean the switch rich). The amount of fuel to add or subtract increases with the airflow mode and should be based on injector size and % fuel switching needed.
Closed Loop Proportional Gain vs. O2 Error: This table returns a multiplier value for the increase/decrease of the base rate table. A multiplier value of 1.000 will have no effect on the proportional base rate. If the difference between the current O2 reading and its desired value from table O2 Rich/Lean vs Mode (the current Fast O2 error) is large the VCM will need to change the proportional fuel a lot. If the error is small, it should change it only a little to continue oscillation without undershoot or overshoot. Undershooting will cause the Closed loop fuel to become sluggish or miss the current O2 Rich/Lean vs. Mode table set point. Overshooting with cause the engine to vary excessively in RPM.

The TPS and MPH values determine the following
- Alternate fuel trim gain behavior during idle
- Idle AFR when in open loop mode

Both conditions must be met for idle behavior to be selected.

Fuel Idle TPS Threshold: Minimum Throttle Position Percent Required
Fuel Idle Speed Threshold: Minimum Speed Required

These two tables affect the STFT time needed for proper closed loop response

Closed Loop Integrator Delay vs. Airflow Mode: This table returns the base integrator delay.
The integrator is a function of the Slow Filtered O2 Error over time, The integrator handles persistent rich or lean fuel conditions based on the slow O2 error and Rich/Lean vs Airflow mode. The Base Delay vs Airflow Mode table is the minimum time in milliseconds an overly rich or lean condition needs to exist before the VCM is allowed to make a fuel correction.
Closed Loop Integrator Delay Mult vs. O2 Error: This table returns a multiplier value for the increase/decrease of the base integrator time delay. A multiplier value of 1.000 has no effect on the base delay. If the slow o2 error is extremely large the integrator will need to act more quickly. If the error is small the integrator will need less control to keep the closed loop fuel switching closer to the current O2 Rich/Lean vs. Mode table set point.

Long Term Fuel Trims

LTFT Enable
LTFT Min ECT: LTFT learn is disabled below this engine coolant temperature.
LTFT Max ECT: LTFT learn is disabled above this engine coolant temperature.
Long Term Fuel Trim Min MAP vs. Baro: MAP must be above this value to enable LTFT learning.

LTFT Boundaries
Long Term Fuel Trim RPM Boundaries: This table defines the RPM boundaries for the LTFT cells.
Long Term Fuel Trim MAP Boundaries: This table define the MAP boundaries for the LTFT cells.

General
Closed Loop Mode vs. Airflow: This table defines the airflow mode the Closed Loop routines use to operate. It controls selection of various gains and delays used to interpret the O2 sensor signals.

LTFT Idle Cells Thresholds
LTFT Idle Cells Enable TPS: LTFT idle cells will be used below this throttle position.
LTFT Idle Cells Disable TPS: LTFT idle cells will be disabled above this throttle position.
LTFT Idle Cells Enable VSS: LTFT idle cells will be used below this vehicle speed.
LTFT Idle Cells Disable VSS: LTFT idle cells will be disabled above this vehicle speed.

Fuel Trims LS1 V8
0 - 15 defined by the LTFT RPM and MAP boundaries
16 - Idle PN (AC on)
17 - Idle PN (AC off)
18 - Idle InGear (AC on)
19 - Idle InGear (AC off)
20 - Idle (EVAP closed)
21 - Coastdown (EVAP closed)
22 - Non-Idle (EVAP Closed)

Usually EVAP closes at WOT hence cell #22 is mostly used at WOT, but you will see it used during warmup (before evap purge begins). At WOT you will also see cell #15 if the EVAP purge opens (ie. vacuum drops enough for the purge to begin).


Fuel Trims LS2/LS7/L76, Cobalt SS 2.0L s/c and other later model vehicles that use RPM/MAP boundaries
The LS2/7 and others have more cells but follow a similar pattern to the LS1:

EVAP Open
0 - 15 defined by the LTFT RPM and MAP boundaries
16 - Idle PN (AC on)
17 - Idle PN (AC off)
18 - Idle InGear (AC on)
19 - Idle InGear (AC off)
20 - Decel

EVAP Closed
21 - 36 defined by the LTFT RPM and MAP boundaries
37 - Idle
38 - Decel


Fuel Trims later LS3 and other later model vehicles that use Airflow Mode boundaries

EVAP Open
0 - 5 defined by the LTFT Airflow Mode Purge On boundaries
6 - Idle
7 - Decel

EVAP Closed
8 - 13 defined by the LTFT Airflow Mode Purge Off boundaries
14 - Idle
15 - Decel


Fuel Trims V6 vehicles
0 = Idle
1 = Decel
2 = Light Load / Engine Not Running
3 = High Load
4 = Med Load

 

Vacuum and fuel pressure perfect
No codes
Runs fine in open loop. It goes into closed loop and thinks the engine is running way lean. It isn't. We can't get the system to stop dumping fuel.

 

I may have gotten the terminology backwards but I think you got jist.

 

No big cam.

TPIS EGR kit installed for appearance only. Is not in the tune and has been physically disconnected for testing purposes. Front cats have been removed. TPIS headers installed. One 02 sensor in system. Has been replaced 3 times now. The one cat left has been removed and is being replaced by a new free flow cat. We thought we may have smudged the old one with all of the way rich running. The old cat looked fine after removed.

Now the hypothesis I have just relayed to the principal mechanic. We put a 160 degree fan switch on this thing because the stock fan switch was at ~230. The car ran insanely hot in the summer and I was always running the AC just to keep the fans on. I am wondering whether a fan on signal at 160 is screwing up the computer somehow. We go closed loop and the engine is running maybe 180 with fans running. Could this create a confusing situation such that the computer is fooled into thinking we are running very hot and lean because fans are on?

 

Ive only had this happen when there was an O2 sensor problem. After installing headers the O2 sensor was not getting hot enough. Was reading lean and dumping gas. This fouls the O2 sensor just like it can spark plugs. Once fouled its done for. It will not clean up. The answer was simple. A heated O2 sensor fixed the issue.

 

Which part #? Does it require modification to original O2 harness plug?

 

Is it a heated O2 sensor? If it isn't it should be with your setup.

 

We are installing heated O2 sensor. Interesting hearing this on this forum but no mention of it from TPIS. In fact we have been using their "recommended" O2 sensor.

 

[QUOTE
=Dave Schotz;1588761305]Which part #? Does it require modification to original O2 harness plug?[/QUOTE]


Bosch Part# 0258003077. Takes a flat 4 wire plug, 12V +, 2 grounds and the Sensor wire. I got the matching pigtail at Pepboys.

 

No luck with heated o2 sensor. Motor still demanding very high amounts of fuel. Now replacing ECM.

 

[/QUOTE]

Many people, including myself have built multi high performance moded TPI based engines. utilizing the OE 02 without any problems after tuning to supporting mods. Did your programmer use speed density mode?
do you have a print out OR back up of your tune?

 

No luck with heated 02 sensor. Now looking at injectors. TPIS provided 30lb Volvo injectors in their kit. Any recommendations on injector brand and pressure?

 

who built the motor, with what projected HP goal. What cam and heads. Zero deck block. Compression? I was using 30# Inj in my moded 355 Holley SR. 11:1, .125 domes, CC306 it was in the 400HP range
it was very lean, I was using a standard AFR meter at that time. It took me hours \ days of adjusting till I dialed it this way.

 

Hal, just picked up on this thread. You might want to run a compression/leakdown test to rule out anything mechanical. A collapsed lifter or soft cylinder can make a motor run like poop. When it is running, shoot the headers with an infrared heat gun to make sure all is firing. You asked many posts ago about how I wired up my Accel DFI. I kept all the dash wiring which is separate from the ecm. The rest was pretty basic just following the instructions from Accel. Just took some cutting and splicing.

 

Here are the engine specs. I have asked the mechanic to provide tuning output.


blue print the engine is a BP3834CT1 420HP 450Ft
10.0:1 Compression
Rollor Rockers 1.6
cam .480 intake / .486 exhast
229 intake /230 exhaust @ .050
34 deg timing at 3500 RPM
deck height not provided
head info
30lb injectors


Part#

H8002K
Intake

Intake Runner Volume (cc): 195cc
Intake Port Location: Standard
Intake Manifold Style: 1986 and Earlier Intake Bolt Pattern
Intake Valves Included: Yes
Intake Valve Diameter (in): 2.020 in.
Machined Intake Runner: CNC-No
Exhaust

Runner Volume (cc): CNC- 75cc
Exhaust Valve Diameter (in): 1.600 in.
Exhaust Valves Included: Yes
Exhaust Runner: No
Port Shape: Square-Port
Exhaust Port Location: Standard
Combustion Chamber

Combustion Chamber Volume (cc): 64cc
CNC-Machined Combustion Chamber: No
Valve Specs

Maximum Valve Lift (in): .575 in.
Intake Valve Angle: 23 Degrees
Exhaust Valve Angle: 23 Degrees
Valve Guides Included: Yes
Valve Guide Material: Manganese Bronze
Valve Seats Machined: Yes
Valve Seat Machine Style: 3-Angle
Valve Seat Material: Chrome Nickle
Valve Stem Seals Included: Yes
Valve Stem Seal Style: Viton® Fluoroelastomer
Springs

Valve Springs Included: Yes
Spring Pressure Open: 295-305 @ 1.225
Spring Pressure Closed: 115-125 @ 1.800
Outside Diameter of Outer Spring (in): 1.437 in.
Damper Spring Included: Yes
Number of Springs per Valve: Dual
Retainers Included: Yes
Retainer Material: Chromemoly Steel
Locks Included: Yes
Lock Style: 7 Degree
Pushrods

Guide Plates Included: No
Guide Plate Pushrod Size (in): 5/16 in.
Rocker Arms

Rocker Arm Studs Included: Yes
Rocker Arm Stud Size (in): 3/8 in.
Rocker Arms Included: N/A
Rocker Arm Nuts Included: No
Misc.

Head Style: Assembled

Cylinder Head Material: Aluminum
Cylinder Head Finish: Natural

Spark Plug Style: Straight – .750 Reach Gasket
Cover Mounting Style: Perimeter Bolt
Accessory Bolt Holes Drilled: Yes
Holes Drilled: No
Oiling Style: Through Pushrod
Machined for O-Ring: No
Heat Crossover: No

 

Please provide specific part numbers re: your Accel system running your mini ram. We are about to abandon the TPIS management system.

Thanks!!