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Discussion Starter · #1 ·
PCM came in today for anyone reading my posts,
Installed the new PCM, no luck.. Car is a fresh rebuild, hasn't started yet.. I tested the spark by removing one of the wires from a plug, grounding it and turning the engine over... No spark. Removed the fuel rail, turned it over, no fuel comes out.. Fuel pump kicks on, there is fuel pressure but no injector pulse. Pulled up the diagram on testing opti's from Shbox, went through it and there is a problem here..

With key on at opti harness

opti plugged in
A=Less then 1v
B=.037VAC
C=12vDC No continuity
D=.028

opti unplugged
A=5vdc
B=5vdc
C=12vdc
D=52.7 ohms :craz28:

According to the chart I should have .2 ohms on D with the opti unplugged, and with the opti plugged in it should be ALOT different... So that makes me think this is either a ground wire or opti issue (Have grounds connected to the stud at the coil checked, cleaned and double checked, ground connected down by starter for pcm, double checked).. Any thoughts?
 

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It might be the security system . I've been reading alot of posts about that causing no pulse or spark . Might check that .
 

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Also check for codes as all the ignition codes don't light the ses, and disable the fuel injectors from opening, as well as, no spark.

Then grab your wiring diagrams, pcm symptoms chart, trouble shooting charts and get going. If you don't have these check thread in this section titled "GM service manuals" and download the 94 manual. Volume 2 will have the info you need. 94 manual has almost all info the same as your 95. For the small differences, www.shbox.com will provide the info.

You will start by confirming that all fuses and fuseable links are in order. Then all power leads to components are in order. Grounds are next. to engine and pcm grounds and power sources are vital.

Next step is to make sure electrical part of ignition switch is sending power on all power leads. Make sure connectors and their pins are good. Not only on ignition switch, but opti harness, sensors, pcm, etc.

Next note, if car is automatic is to check the main transmission wire harness. This is because the trans gets it's power from the same source as coil & icm. If there's a problem with the trans electrics, or its wiring, it can pull down power to the coil & icm.

Watch the diagnosing the opti video, found in lt1 engine section sticky threads, and run tests.

Download Gary Dougs obd1 scan program, located in 4th gen section and get yourself a cable to connect car's dlc to usb of laptop or note book. Get cable at the following source; ALDL OBD1 OBD cable OBDI OBD2 engine codes $59 plus shipping. I suggest Gary Doug obd1 scan because from what I understand of the program, it can tell you if low & high resolution signals in opti are being produced. I would pm GaryDoug to make sure before spending money on the cable. However, even if program doesn't detect opti pulses, it's still a good scan and code program. You can also download the trial version of DataMaster at the GM manual link in 4th gen section. And freescan is also available from me.
 

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Casey, looking at this diagram as a reference: http://shbox.com/1/95_ign_system_schematic.jpg The Ignition System Test Connection is what everyone calls the harness.

If post #1 test was done with harness pulled from opti and reading harness end pin D to the PCM w/key off then 52 ohms is bad.. Try the test below and see if it produces correct results, if Pin D is not at correct ground level then none of the voltage tests will read correctly..

Pull the opti harness connection at the top up near the evap solenoid, turn the key on and use a digital voltage meter (DVM) set at Voltage range. We will be testing the harness pins going to the PCM. . Put the negative lead on pin D (reference ground) and test pins A & B for 5 volts coming from the PCM, then test pin C for +12 volts from the PCM (actually reads about 11.8 volts). If all are good then turn off key and test the resistance of D to ground stud on right wheelwell s/b .04 ohms or less. If readings are good re-connect harness at top and pull the harness off at the opti and repeat the same key on voltage/ key off resistance test of the harness end to PCM. That verifies the harness is good.

Did not read previous posts you mentioned was the OPTI ever replaced ??
 

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Discussion Starter · #5 ·
Forgot to mention in the first post that I did run cats tuner, disabled VATS in the new PCM, and it is not popping up any DTC codes in data master. It also is not telling me anything about spark in monitor mode when I try to crank it over.. Also have gone through the fuses, they are all good I did that test,
Only differences are I didn't use the d wire for a ground, and opti harness is hard wired into the PCM so I took the harness apart right up by the injectors where the harness would normally plug in.. tested all the wires using a ground stud. .. Made sure the connection was good before testing it..
a-5v
b-5v
c-12v
d-52ohms

Opti was replaced last year with MSD pro billet.. Long story short it was acting up with opti symptoms when I put it in the shop, the guy at the shop assured me that they tested it and the opti wasn't my problem. Seal was rolled on the new opti we found out when it was installed. Dont really trust that guys word though.


Im thinking that ground with so much ohms might have something to do with it, it all really makes no since to me, what would make it have 52ohms?

so today I will run more tests I guess and trace that ground back to wherever it goes to make sure there is nothing wrong with it..
 

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Does Datamaster show RPM with key on starter not running, it should read 50 RPM, desired idle = 3188. MAP = 100 Kpa .. Then turn to start, when starter engages Datamaster should show RPM at about 300, injector pulse width should start at 40 Ms and go to 60's, IAC s/b near 140, spark advance about 10, If RPM and BPW are not correct the PCM is not seeing opti pulses.. If so we need voltage test results from post #4.
 

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Discussion Starter · #7 ·
Bobdec, I wish I would have known to pay closer attention to that a couple days ago when I had my comp up at the shop, seems like the RPM's were off though, I just thought it was because it was starting. shows what I know...
But I decided there is too much evidence that points to the opti for it to not be the opti. Ran the tests on the wires again, found the problem with the ground, ended up being because i didn't have the motor grounded to the body well enough so I ran another ground wire and cut the PCM ground wire back a couple feet and attached it to the manifold. Brought the ohm's down from in the 50's to .2. Then I tested the opti again, there's just not enough communication voltage coming out of the opti according to all the charts and stuff. I ordered a cheap unit from rockauto thats supposed to be here tomorrow, knock on wood, hope it's a good enough one to last untill I can send my MSD opti in and get it redone.
 

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Discussion Starter · #8 ·
Turns out it was the opti,
Ordered a cheap one to hold me over untill my MSD is rebuilt. Put it in, turned the key, and it fired right up.. New dilema.. when I started it up for the first time I let it run for awhile and tried to get the air out of the coolant system.. Motor heated up to 242 max, before I shut it off. Opened the bleeder screws, recirculated everything, let it cool down, re heated, let it cool down. We spent a couple hours trying to get the temp gauge to stay put around the half way mark. Took the thermostat out, restarted it, it got better, but still likes to hover around 240 degrees with no load, in neutral and the tires in the air. I think the motor is running lean because I put a different cam, new heads, new pistons, and bored it to a 355, also because the headers get red hot in a hurry with the motor running at 1300rpm's.. I wonder if the motor running lean could cause a overheating problem?? Already plugged datamaster into it, really have no idea what im looking at or for at this point.
 

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pm me with your e-mail address and I'll send you the pdf file of "sensor readings and what they mean".

Yes the things that will make your headers glow cherry red are; lean mixture, retarded ignition timing, wrong crank-cam timing.
 
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