BurberryEd

383 with Comp Cam & Roller Rockers, Professional Products 58 mm Throttle Body, Bosh 111 32 lb Injectors, Bailey Engineering LTCC Coil per Cylinder Ing., Short Headers no cats or resomator, PCM of NC Tune(Prom). Engine will not run below 1500 RPM. Have done the IAC Mod on the Throttle Body, Replaced the IAC & Replaced the Intake Gaskets. All spark plugs are firing & injectors working. Fuel pressure holds 40 lbs. Vacuum is low, all fittings plugged. AC, EGR & Air pump have been removed. Unable to post log. At 1500 RPM, Open Loop: Map Kpa=93.7, Fuel Trim Cell=18, Long term & Short Term Counts=128, BPW ms=6.59, Inj Dc=17.3, O2 mv=457/453, TPS %=13.7, Tps Volts=1.33, Spark Advabce=33, Knock Count=2563, EGR DC=0.0, CCP DC=0.0, IA Temp C=10.3, AC Temp=NA, AC Press PSI=18.8, Idle RPM=1050, IAC Position=160.No Codes. LT & ST Counts do not change. O2 sensors, TPS, Spark Advance, Knock Counts all change. Have set TPS & reset IAC. I do not know what the Values should be other than the IAC is maxed out, TPS & O2 seam OK. Engine will start & die and then the throttle must be fully open to restart. Smells Flooded. I have been working on problems with this Engine/ECM for several months. Any HELP will be Greatly Appreciated.

bjankuski

The car is is open loop because the vacuum is so low. I would suspect that the timing is off, I know your scan says 33 degees, but can you verify the actual timing to see if what you are commanding is actually being delivered.

Cliff Harris

Your TPS is messed up. 13.7% and 1.33 volts is way too high. The voltage should be around 0.7 volts with the throttle closed. You can measure that with the engine off, either with a scanner (the preferred method because that is what the PCM sees) or with a voltmeter. That would explain your high idle RPM -- the ECM thinks the throttle is partially open. LT1s don't usually need a minimum idle adjustment, but your setup is not stock so you might need to do something similar:

http://forums.corvetteforum.com/1570563689-post1.html

The LT and ST values are held at 128 in open loop mode, so that is normal.

BPW (Base Pulse Width) of 6.59ms seems high to me, which would explain the rich condition, especially with 32 lb injectors. That's a good size for your engine, so you're OK there.

The knock count makes no sense. It can't be that high. If it's over 10 you have problems. Maybe you have the wrong scanner template for your car.

The computer determines what the IAC count is. There is no reset procedure because the PCM resets it every time the ignition is turned on. The PCM uses the IAC to set the idle speed. It also uses it to maintain the AFR in closed loop mode, but you're not there yet.

I don't see coolant temperature in there anywhere. That is the most important parameter and it is the basis for how the PCM controls the two main engine controls: the injector pulse width and the timing, among other things.

Your O2 sensor is not yet hot enough to go into closed loop mode, so its readings don't mean anything until you're in closed loop mode.

BurberryEd

TPS readings are at 1500 RPM. .54 at idle. Engine temp was 22.3 C.

bjankuski

This is why I suspect timing, you need a lot of throttle to keep the engine running and it is not making much power since the vacuum is so low at the 1500 RPM. The timing appears to be off or maybe your firing order is out of wack. I have seen guys put the opti back in incorrectly (jammed it together) and it runs but the timing is way off.

BurberryEd

I opened the engine already to check the crank to cam timing and the optispark. I did not pull the opti in with the bolts, it went in flush. May need to take it apart again. I built an LED light box to check the firing order and it was correct. I think that I would need to bring #1 cylinder to TDC and place a mark on the damper and then make a pointer in order to check the timing with a timing light? Is there another way?
I really appreciate any help.
Ed

ezobens

Any chance the cam you are using is a bit too large for your application and is creating the low vacuum?
EFI doesn't do well with large duration / overlap cams.
Just a thought.

bjankuski

That is what you need to do but it is not so easy to find TDC on an LT1. What I did was pull off the rockers on cylinder #1 and apply 100 PSI to the cylinder and let it find BDC, I then marked the balancer at 180 degrees from where I put my pointer so I could find TDC with the engine running. After the TDC is found you can use an adjustable timing light to see what idle timing you are getting and compare that to what you should be getting and see if there is an issue. To make this easier I set all of my timing at a fixed 20 degrees in the tune and then checked with the timing light, to see if I was at 20 degrees.

THE 383 admiral

I Returned a Professional Product LT1
TB due to a open throttle. That would not close. OE cable.
I could have easily made a cable. As I did after eliminating the ASR.
Also they drilled a proprietary bolt pattern for the top plate.. plus non sealed bearing.
UN professional.

BurberryEd

60 Degrees Advance @ 1500 RPM, would you assume that the Optispark is not installed correctly? Can the Chip in the ECM cause that much Advance?
Thanks
Ed B:

THE 383 admiral

No the maximum timing is controlled in the contents table @ 46 Deg, the main timing table @ 1500 RPM 40 Deg is max from 30 - 50 Kpa + or - approx 2 Deg.

BurberryEd

Pulled the Optispark to make sure that it is installed correctly. Looked correct. Pulled the cap this time to make sure that it is installed correctly. Still same issues. If the Eprom is program is not correct could it thesee this problem?
Thanks
Ed B

THE 383 admiral

did you get your prom flashed? Why would the timing tables be turned up over 50 Deg.

BurberryEd

Yes, PCM of NC flashed it.
Ed B

THE 383 admiral

did they send you a print out?? Or a backup copy of the new bin???

BurberryEd

No they did not. I will request a print out or back up.
Thanks
Ed B

pkincy

If you send me a pm, i will respond with my email so you can send me the bin file.

I can file compare to my running perfectly 93 383 Y Bod. I will need a file that can be opened with Tuner Cat.

pkincy

Btw, i expect it is least likely to be a tune problem and most likely to be a mechanical problem, leak, sensor, etc.

BurberryEd

At last it is alive and well. Tying the sensor ground to ground causes a lot of problems!!!!!!!