Roscoe's 85

I was driving my 94 LT1 6sp home from work yesterday (about 38 miles) and it all of a sudden died. I got it started again after a fair bit of cranking but then it died about 5 minutes later. I hopped a ride back to my work and picked up our scan tool (Modise) but when I tried to hook it up it would not even turn on. I thought maybe the battery is to weak so I jumped it and the Modise turned on but would not connect. After jumping the 4/12 pins I get some history codes of H16, H36, H42, and H62. Earlier this year I changed out the opti with a Dynaspark as well as changed the coil and ignition module. It ran great for a few months. Any ideas??? I hate to have it towed. It's gonna be some big $$

rick lambert

I'm assuming (hate that word) you've looked up the codes? First thing I
would check -fuel, can you hear the pump priming?

Roscoe's 85

Sorry but I haven't been able to get to my manuals to look up the code. Can someone help me with that. I did a search on here for the codes and the only one I got something on was the H36 which is ignition related. Do you think the fuel pump is bad or the relay? I will try to put a gage on it to see what the pressure is. Thanks for any input.

williammackean

Sorry about the troubles!

I have found it worth paying the $10/year to have Emergency Roadside Assistance on my insurance. I have used it twice in 10 years. @ $80/tow, I'm money ahead. If I didn't have it, my insurance was not going to pay to have my totalled truck towed to the boneyard.

-Kyle

Fozzy_Bear

I would check the fuel pump first. Then, correspondingly, the fuel filter. Or thinking a bit further about it, if you check the fuel rail pressure you will be checking them both at once.

thomastl

A couple of quick things to do on the side of the road.

1. Remove cover on fuel schraeder valve and push down the valve w/ the key on to verify you have fuel pressure. If not - check fuse. If good - you might try adding a few gallons of gas to see if the pickup/pump will now pickup fuel. If not - you know the problem is the fuel pump or pressure regulator.
2. Disconnect battery and leave disconnected for about 10 minutes to reset computer and put into default mode. Usually the car will run for a little bit on default mode w/ most any sensor bad.
3. If this don't work - you probably have an ignition problem in the coil or dynaspark. Make sure you don't have any wires that have come disconnected or a ground that has come loose or a major vacuum line that has come loose.

Other than that - your looking at a tow to get it where you can do further diagnostics/work on the ignition system.

sami85L98

Iam with Thomast: Disconnect battery for a couple of min's than reconnect it, this will clear error codes and u should be able to start again, gone through same situation on I-75 about 200 miles away from atlanta could have been a nightmare if it would have not started, sometimes quck thinking save lot of $$.

RAGOVET

http://www.gnttype.org/maint/malf.html

Hooked on Vettes

There are two timing signals that are generated by the Optispark and go to the PCM for processing that eventually determines the timing to fire the spark plugs.

Low resolution signal is 4 pulses per one crankshaft revolution.

High resolution 180 pulses per one crankshaft revolution.

The engine can still run if the High resolution signal is missing.

DTC 16 The PCM detects 720 high resolution timing pulses before any low resolution pulses are detected.
DTC 16 will be stored in the PCM memory, but will not turn on the Malfunction indicator Lamp. Fuel pump and injector operation will be disabled.

DTC 36 sets when 40 low resolution pulses occur before any high resolution pulses are detected.
The engine does not need the high resolution pulse to operate. DTC 36 will cause the Malfunction indicator Lamp to illuminate.

DTC 42 PCM detects 84 crankshaft revolutions with out any Ignition Control activity. This would happen because the PCM is not providing any pulses to the Ignition Coil module since no Low resolution pulses are coming from the Optispark or it could be the PCM is not processing the low resolution signal from the Optispark properly.

According the the Helms manual, if DTC 16 and DTC 42 set at the same time and the four pin wire connector at the Optispark that eventually goes to the Black connector at the PCM are making good contact, to replace the PCM. (Visually examine the wires for any exposed insulation that could cause a short and verify all connectors are making good contact).

If you don't have a scope to look at the low resolution signal, the only thing you can do is use a volt meter to measure Pin A at the ignition system test connector.
That is the four pin connector at the Optispark. It has four wires.

Pin A Red Black wire Low resolution signal
Pin B Purple/White wire High resolution signal
Pin C Red wire Distributor ignition feed
Pin D Pink/Black wire Distributor reference low signal

Ignition off. Disconnect ignition system test connector.
Ignition on. Using Volt meter on DC scale, measure voltage on Terminal A PCM side of the test connector.

If Less than .5 volts Faulty PCM connection or Faulty PCM.

If you measure 4 to 6 volts and the wiring appears to be good the Optispark is bad.

If you measure over 6 volts the low resolution signal Pin A Red/Black wire is shorted to an external voltage source. (Not likely).

DTC H62 Engine Oil Temp. Sensor Circuit.
Time since engine start is 30 minutes and signal voltage indicates engine oil temp. is greater than 284F.

The PCM uses the oil temp. info. to control A/C clutch and engine cooling fan. Info. is also use by the CCM to determine when to change the engine oil.

I don't see how DTC 62 can be related to your current no start problem unless the PCM is bad.

Roscoe's 85

Thanks for all the help!! It sounds like it is either the fuel pump or the PCM. Even though I have very low fuel pressure I am leaning towards the PCM since the scan tool went crazy when I tried to hook it up. It wouldn't even load up to the main screen (I tried it on my truck and it worked fine and have used it on this vehicle in the past). This one is gonna hurt the pocket book...$$$... Anyone know how much a new PCM is? Can they just reflash it?

Roscoe's 85

I had the car towed to a nearby mechanic and he says that the "opti" went out on it. I find that hard to believe since I put in a Dynaspark about 2 months ago. I followed ALL of the directions to the letter. Has anyone else had a Dynaspark fail? I guess now I will get it towed home and pull out the Dynaspark to see what the deal is.

bogus

Considering that DynaTech buys their electronics from the same place GM does, I would not be surprised that there was an electronics failure.

The H16 and H36 tell me that something was amiss with the DynaSpark. I would like to think those codes are not left overs from days of old.