ok, i just checked the voltage again and it looks normal this time at the MAP. i also used a mity vac with 10 hg as don mentioned and volts dropped from 4.88 to 3.oo, so the MAP is good.

i do not have a scanner so i'm not sure how is the best way to check the readings at wot under load?

also fred, you mentioned the hub is not keyed so i'm sure the guy who replaced the distributor cap on it 7 years ago might not have put it on correctly. since i was at 3 o clock with #1 closed and every consecutive cylinder was off by 90 degrees, should i rule out the timing issue? car idles fine and will pull hard with no issues revving the motor, but under load it stumbles.

what about opti? mine is at least 7 years old and i believe they only changed the cap when i bought the car in 2001.

 

ok, new development: just after testing the MAP, i tried starting the car and it croaked. starter is turning over, but sounds like its gasping for air. i checked fuel pressure KOEO - 41psi steady. coil, plugs, and wires are less than 1 year old all ac/delco.

went back 10 mins later and it started up ok. does this sound like the ICM going out, or more like opti?

 

If he installed the Opti with the odd-tooth on the splined drive shaft in the correct position, it doesn't matter where the damper pointer was pointing. The Opti is aligned correctly by the driveshaft. You don't need to reference TDC when you install it, unless you want to verify that you got the splined shaft in correctly.

 

thanks fred.

i think the problem is narrowing down a bit: just after testing the MAP, i tried starting the car and it croaked. starter is turning over, but sounds like its gasping for air. i checked fuel pressure KOEO - 41psi steady. coil, plugs, and wires are less than 1 year old all ac/delco.

went back 10 mins later and it started up ok. does this sound like the ICM going out, or more like opti?

 

update:

checked the ohms at the ICM: over 10.
checked the ac voltage at the ICM harness while cranking the car: 0.35 volts

looks like opti is failing to send enough to the pcm? according to shoebox's write-up voltage should be 1-4 while cranking. harness and wires from opti look pretty good.

does everyone think it's narrowed down to opti? car is also intermittently starting. croaked once, then started up, then croaked again.

 

If its stalling or not starting because of loss of the low res pulse signal from the Opti, it should be setting a code (DTC 16) in the PCM. Personally, I'd spend the money on a scan tool or some scanning software, before spending large amounts of money on replacement parts.

 

fred, i have a scan tool - an innova 3120, but it's not pulling any codes nor am i seeing a check engine light. the scan tool indicates "vehicle not responding," and for DTC's it says no DTC's stored. is there something wrong with the pcm/connection? confused what it says vehicle not responding.

i also have a newer laptop with windows vista. what software do you recommend i download?

 

If it can't connect to the PCM, its not going to be able to tell you if you have codes. Have you checked the cigarette light fuse? Some scanners pick up +12V from a pin on the ALDL connector. Usually, that pin is powered by the cig lighter fuse.

Free software is TTS DataMaster (20 free uses) or FreeScan (completely free). Cable from AKM cables:

http://www.ttspowersystems.com/
http://www.andywhittaker.com/
http://www.akmcables.com/

 

cig lighter works ok, so i'm not sure what is going on. i looked at the pcm connector slots on the port under the steering wheel and i see three with metal slots. my gm obd 1 connector on the innova has 12 blades. it slides in smoothly, but i'm lost as to why it wont read anything. it reads my obd2 g8 gt perfectly.

i'm going to download the scanning software you supplied above.

also, when the car did start up yesterday (after failing once) i had no service engine light. so can a opti fail and still not trip a service engine light?

 

update: tested the voltage at the grey opti harness with the wires connected (intake manifold area)

wire A: 0.25 V
wire B: 0.25 V
wire C 11.5 V
wire D 0.06 V

what does this point to?

 

D on the pink/black wire is ground. C on the red wire is battery voltage so you are low but forget that for a moment.

B on the purple/white wire is hi res feed back from the opti to the PCM and A on the red/black wire is the low res feed back. So you could have caught both of them (low and hi) in between signal pulses. Both of them go between 0 and 5 volts DC. Although the low does it many less times than the hi res does.

To see if they are both working, you can either use your meter while you slowly rotate the engine over. Or simply scan for codes since the PCM will monitor those 2 signals for you. No codes means they are working.

You should also check the battery voltage with the car in the same condition it was when you measured pin c above at 11.5 and see where you are loosing voltage. Remember to check the quality of the connections on both battery voltages signals and grounds through out the engine bay.

 

thanks don.

i will try A and B again while someone cranks the ignition. what voltage would point to a bad opti on A/B? as for the C/battery voltage i think it drained a bit with all the attempts at starting. it's only a 1 yr old ac delco battery.

as far as the pcm, i'm very perplexed by that. no code, yet my code reader is unable to read the pcm at all. i installed freescan, but my laptop is vista and it's giving me errors, so not much help there.

 

You won't be able to use a meter to see the low and hi res signals as you crank it with the starter. The pulses will move too quickly to register on the meter.

You can only use a meter and rotate the engine by hand. So you will probably have to take the plugs out to do so.

Don't forget to confirm the battery voltage compared to the bat voltage at the opti.

Why do you say it has no code but yet you are unable to scan it??? How do you know it has no codes? Because the SES is not lit? The more major fault of the opti feedback signals DTC16 will not light the SES. Yet it will shut down the injectors and the fuel pump.

So if you want to check to see if it is the low res signal problem, monitor the injector pulses while the problem occurs. But I highly doubt the low res signal is coming and going to cause your stumble.

 

i will check the batt voltage as you recommend.

as for the pcm i guess my assumption was not correct. i always thought a code = ses light. i have no ses light, yet when i plug in the innova 3120 code reader it says unable to link to pcm.

also, if the dtc16 was stored on the pcm you mentioned it would shut down the injectors and fuel pump? when i turn the key to "on" fuel pressure at the regulator is at steady 40/41 psi. how do i test the injectors?

last weekend i did the following as well: checked the ohms at the ICM: over 10. checked the ac voltage at the ICM harness while cranking the car: 0.35 volts

looks like opti is failing to send enough to the pcm? according to shoebox's write-up voltage should be 1-4 while cranking. harness and wires from opti look pretty good.

 

The 1 to 4 volts you are speaking of is the Ignition Control line(white wire) from the PCM to the ICM. It is 1 to 4 volts AC. Since your car runs, don't worry about it. It, like the opti's DTC 16 will not light the SES if it has a problem. It would have a code for it.

You are confusing the opti's 2 feedback signals which vary from 0 to 5 volts with the IC signal which goes from the PCM to the ICM. I mentioned the feedback signals (low res and hi res) earlier.

The first thing to do is see if the DTC is recurring. That fact that the engine runs but hesitates indicates that the DTC16 is NOT a hard, constant problem. Otherwise the injectors would be shut down as well as the pump. If the DTC 16 returns after clearing all codes, you must address it first and foremost. IF it does return even though the engine is running probably means you have a wiring or connector issue. You would look at ALL the connectors from the opti to the PCM and be sure to tighten the pins up for a good contact. BUT again, only if the DTC returns.

I guess at this point you will need a trouble free way of retrieving codes.

And don't jump around looking at all different items until you have addressed and eliminated one thing at a time.