LS1LT1 Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
Hey All, i have a LT1 with LT4 heads and gm hot cam kit with 6 speed in 1957 belair, harness is fuel injection connection and all input/output sensors have been replaced, Engine rebuilt and first time run. so now here is my problem, engine runs and idles fine although on the rich side while cold, once at operating temp (176DEG) Engine begins to run super
rough and stalls out but will start back up and run for a few seconds then stalls. if left to drop to 160 degrees will start and idle/run until 176 degrees.
here are some specs cold and then hot = fuel pressure 38 psi- 43 psi with vacuum removed, left H02s bank 2 - 0.85 to 0.89 v, right H02s bank 2 - 0.84 to0.88 v then hot left H02s - 0.84 to 0.89v and right H02s - 0.0v. i ohm'ed the injectors
cold then hot and they were #1-16.7-17.1 #3-16.7-17.1 #5-16.7-17.2 #7-16.7-17.2 #2-16.7-17.3 #4-16.7-17.2 #6-16.6-17.3 #8-16.8-17.4. I swopped 02 sensors left to right and it made no difference.
Any help would be appreciated, Thank You.
 

·
Global Moderator
Joined
·
13,559 Posts
Since your car runs well until 176 degrees, I believe you have a closed loop running problem.

When cold engine operates in open loop. Open loop uses a few sensors for pcm to control air/fuel ratio. Since you have not said what year your lt1 engine is out of, I don't know if pcm system is obd 1, or obd 2.

I suggest you doing a running sensor scan to see what all the sensor data is. To help you out, download one of the following years of factory service available at following link. We have 93, 94, 95, & 96. If your lt1 is from a 97, the 96 manual will work just fine. www.mediafire.com/?40mfgeoe4ctti

In addition, vacuum leaks and exhaust leaks are a major cause of poor air/fuel mixture.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #3 ·
cocobolo95 thank you for your response. Engine is 1995 with lt4 heads and hot cam, headers are shorty style and had several leaks in the manufacturers welds which i welded up as they were ahead of the 02 sensors, i have done a vacuum
leak test and found none and system is OBD1. even in open loop it still seems to run on the rich side but will idle and accelerate ok. I did note that inj pwm bank1 ranges from 3.9 to 5.1 in closed loop and inj pwm bank1 ranges from 22.8 to
27.8 in closed loop at idle and176 degrees.????
 

·
Global Moderator
Joined
·
13,559 Posts
On next running scan, pay attention to blm's See how much they are above or below the 128 mark. See the coolant temp that sensor displayed. It should be close to the temp gauge reading. Throttle position sensor reading to see if throttle open matches gas pedal position. Get MAF reading, MAP reading.

I just noticed from your O2 sensor readings, they are abnormal. The one bank with 0.84 to 0.89 should be quickly changing above and below the 0.45 volt median. If you used multimeter to check O2 voltages, let your obd 1 scanner tell the story.

The O2 that's reading 0.0 volts is plainly not working. Did you hook up the heater wires od both O2's? Is the scanner data showing PCM switching from open loop to closed loop operation?

For O2's readings below 0.450 indicates lean mixture. PCM will add fuel those increasing injector pulse width.
For O2 readings higher than 0.450 indicates a rich mixture. PCM will sutract fuel. Thus lowering INJ pulse width
BLM at 128 = correct mixture.
BLM at higher than 128 = lean mixture.
BLM at lower than 128 = rich mixture.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #5 ·
PCM is switching from open to closed at 176 as viewed on scanner. In open loop blm at 119 degrees was 18 and
lt ft bank 1 was 128, lt ft bank 2 was 128. this system has no MAF. when going to closed loop BLM goes to 16 and states "enable" yes, lt ft bank1 drops to 108 as does bank 2. closed loop st ft b1 fluctuated between 126 and 203 and b2 68 and
138.
TPS was 0% @ 805 rpms, open loop inj pwm b1 was 5.5 and b2 was 5.6 and when switching to closed loop inj pwm b1 was 3.7 and b2 was 21.4.
barometric pressure was 30.0hg and volts 4.84, MAT was 90degrees, MAP open was 21 with v @ 3.19 and closed
was 19 and v 2.95
 

·
Global Moderator
Joined
·
13,559 Posts
Without a MAF, you PCM is running in speed density mode only. The maf is vital for PCM to run engine as it was designed.

My 90 camaro runs in speed density mode. It alwas has rich exhaust.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #7 ·
yes it does seem rich when in open loop but at closed loop it stalls out and even with speed density it still should run close to normal all be it richer. i will bee doing some checking of the harness wires and pins and if that checks out i will look at the pcm and the chip. am i on the right trail and if its pcm or eprom chip who is a good supplier
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #8 ·
if an engine has no MAF and it is running as speed density does it run in open loop 100% of the time or does it go to closed loop. If it is the case that speed density is open loop 100% does that mean it should not show as going to closed
loop, If that were so it should have been taken out by the tuner that built the ecm/chip ????. Thank you
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #10 ·
That is correct, no MAF but another site stated speed density ran in open loop only which i did not think was so but thought i would ask the question in case i was wrong in my thought process
 

·
Global Moderator
Joined
·
13,559 Posts
My 90 camaro fuel injection is no MAF type and runs speed density. When I hook aldl to a scanner that does running sensor scans, I can watch open loop change to closed loop operation as one of the data streams.

Now, if your PCM was tuned for speed density, with only open loop operation, then it would not go into closed loop operation.

You can hook your aldl to an obd 1 scanner that does real time sensor data. One of the data streams will be weather engine is in open or closed loop operation. The change usually occurs in the 160 to 180 degree range.
 

·
Registered
Joined
·
80 Posts
not quite sure what the obd1 reads for code for optispark is
but something i learned is my camaro had a opti code and a bunch of other codes
but running great for 5 minutes it would smoke the tires all the way around block
then stall and not start for 4 -8 hours
the stall i can do pretty much do any thing to my z and it will run like crap but it will run as long as its got a good opti
the air density thing does not work cuts like half the power.
and ive got a grounded o2 sensor plug and cant tell driving it
went through 4 different brands of plug wires all said low impence or low ohms lol
car would not do a burnout all were cut for old chevy small block
with distributor of on side
i bought a set of morosos put right side on car would smoke them for a mile dumping clutch
but not off gas peddle alone
put other 4 on and its back to former glory lol
went and tracked down the super sport ls1 camaro ss that called me out
and took off it was impressive getting to actually watch him for a change
but knew with a hundred mile an hour top end had no chance barely caught him to get phone number.
So we ran from a dig and I smoked him lol
He called me on the phone I said hello and he goes f888888888ck and hung up lol
 

·
Global Moderator
Joined
·
13,559 Posts
The opti codes for obd 1 are 36- high resolution pulse missing. And 16-low res pulse missing. When code 36 sets, car will still run. When code 16 sets, no one condition.

Besides opti codes there are 2 icm codes. code 41 & 42. Both of which will leave car inop.

Thing about opti sensor & icm is, when solid state electronics are starting to fail, but haven't conked out all the way, both will let the car run until they get hot, then they will fail until they cool down

Forgot to add, when both low & high res pulses fail, no code will set..
 
1 - 13 of 13 Posts
Top