Hey guys I've been struggling trying to figure this out. Starting a month back driving down the road the car would loose power for a split second and come back it did that a few days at random. Then a couple of weeks ago I died at a light struggled to get it back going. No check engine light. Now not confident in driving I've been trying to troubleshoot.

When it dies you can immediately hear the fuel pump cycle. But it would cycle multiple times at different intervals seemed strange. Threw a gauge on it and it holds 42 never drops below when priming it gets close to 45. I've had issues in the past so I also changed the icm. Ohmed out the coil shows good. Checked ground on the pcm to the passenger side of the block. The ignition switch wiring looks good. I have an remote start on the car which bypasses the switch and the car would still not start. I bypassed the remote start to be sure that was not immobilizing the car.

Yesterday while troubleshooting I could not get the car to start so I checked for spark at the coil, i had it. Checked for spark at the plugs and once it arced to the frame the car started (strange). Connected the laptop back up to run scan9495 and I have code 36 which I never had before last night. From what I read code 36 should not cause the car to stall but recent posts seem to saying there's a chance it can. I didn't have this code until today. When I ran scan9495 earlier in the week it would randomly flash random dtcs but never activate the light.

Poking around on scan9495 I noticed my ignition volts seem to be dropping. I read that's the battery voltage to the pcm? My guess is when that voltage drops longer the car dies? Or when it's not there the car does not start?

Any ideas?
Thanks


The car
95 lt1.
Lt4 hotcam
1.6 rockers
Hooker long tubes catless y borla muffler
Mail order pcm tune with lt4 knock module
Engine was rebuilt about 10 years ago with some head porting
Ram air conversion
Air pump delete
Opti is about 12 years old with around 12k on it.
Walbro 255 fuel pump
160* thermostat
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Have you checked the 12 volt wiring to the PCM? Loose? Damaged connector pin? The PCM can't operate below 5 volts. But it should set a code for low voltage (DTC 50). But if it's a total loss of voltage at that short period, maybe it can’t set the code.

The fact the fuel pump is starting intermittently would also seem to indicate the PCM is briefly losing 12 volt power or ground.

The PCM has two grounds. As I recall the second ground is on the stud on the driver side head that holds the ICM/coil bracket. Check the wiring diagram in the factory service manual. See near the top of this PCM diagram for the grounds to the PCM connector. The factory service manual will show the ground number and location. It will also show the splices and any intermediate connectors and where they are located.

http://shbox.com/1/1995_pcm1.jpg

There are also four PCM pins that receive 12 volt power from 2 different sources. See near top of this diagram:

http://shbox.com/1/1995_pcm3.jpg

You should also be concerned about the 20 volt spikes. That may be related to a problem with the voltage regulator in the alternator.

The PCM is not going into closed loop. It should be, because the coolant temp is high enough and the run timer (206 seconds) to time out. But it can’t go into closed loop because the driver side (Bank 1) O2 sensor is “not ready”. Seems it may be stuck at close to 0.450 volts, which would indicate it is not active.

The Bank 1 long term fuel trim (LTFT/BLM) is bottomed out at 108 (pulling out about 15% fuel), the lower limit for that correction of a rich condition.

MAP looks a little low, although part of that could be due to the LT4 HOT cam.

 

Hey Injuneer, I have not checked the specific 12v pins for the pcm getting voltage, I did reseat all connectors earlier in the week. Both grounds I have taken off and cleaned this week as well the one down on the passenger side of the block and the drivers head at the icm.

I didn't even take notice of the voltage spikes. I had my battery tender hooked up during this I'll have to test without that and if it's still there replace the alternator then.

The pcm does attempt closed loop but rpms start dropping and it bounces out of it. Both o2s move up to 6xx mV before it goes into closed loop.

The long term fuel trim I do not know anything about.

Tomorrow I will check all 12v connections. I guess my main concern should be getting the voltage stable and that should solve my shutting down and not starting issue. After that then focus on getting the car to run properly.

Thanks for the assistance I appreciate it.

 

Went out today for a few hours to troubleshoot to check the voltage to the pcm.

B15 and b31 were there and solid no matter what I did.
B30 is there when ignition is switched on. Seems to no be as solid bounces around .1 volts ish if I move the blue connector on the ignition switch (connector is good and not burnt)
D3 was around 9 volts. Traced the wiring and found connector c230 at the passenger kick panel. Found corrosion on the pins, from I'm guessing water. Cleaned them up and now I have a good 12v at the pcm.

Reassembled things and car would not start. A few minutes later after checking everything over it started right up no check engine light running smooth.

Hooked up scan9495 ran the same ignition voltage and tps volts. And saw this. I shut the car off around the 360 second mark and put the key in the run position to monitor the voltage after shutdown

The voltage spiking in the 20s still but no crazy drops to 0.

So I decided to troubleshoot the voltage issue.
Disconnected the alternator and ran on just battery.

The spikes still happen with no alternator. The car was also hard to start and threw the 36 code again and 42.

So then I reconnected the alternator and started the car (didn't want to start again) and while running I disconnected the battery. The spikes still were there. Code 36 still there as well.

After that I put my original icm back in and checked wiring at the icm coil. It looks like at some point the wires got hot the ground lines were stuck to the other lines. None of the copper look to have broken through the shielding. I separated all the wires and went to start the car again. Hard to start yet again it seems hard to start when the 36 code is on. Not sure why 36 keeps activating. Maybe it's when the voltage is lower in the battery since it's not really getting charged much with all this testing. Couldn't look at scan9495 again as my laptop battery died.

So the voltage drop may be fixed. The spikes aren't. Still scared to drive and get stranded. I was thinking of throwing some new fuel in since the stuff in it is probably from around July.

 

Back again with more info.

Charged the battery up last night with my tender, put 5 gallons of fresh fuel in. Checked all plug wires to see if any were touching any metal. I was wondering if a plug wire arcing to ground could be causing the voltage spikes.

Attempted to start the car it was rough at first but got it going and it idled smooth. Drove around a bit in my neighborhood then went to a empty area where I could open it up a bit. Everything felt fairly normal. I had scan9495 running and saw a bunch of spikes (maybe arcing still?) and some drops but not down to 0. the entire time the car had code 36 69 and 70. I recently changed my ac compressor and it was running fine last week but does not now. Still has pressure though the ac is not my main concern at the moment.

Here's how it ran for close to an hour. Went into closed loop dropped out sometimes while idling


I then made it home shut down and cleared the dtcs everything cleared fine. I went to restart and the car was not having it at all.

Threw a code 42 after that. I have not troubleshot anymore after that.

 

I'm wondering if you have excessive interference on the wire to the DLC. I never use the chart option, but it's easy to spot the impossible/false data values in a complete data log. Will also typically produce spurious random DTC’s that only last for one frame.

 

How can I view logs myself?

Went out again today since I had the day off. Car initially started right away normally then died after about 10 seconds. Couldn't get it going again sputtering and not firing. Did the code 42 check list and all wiring checked out good. Called for the icm. Tried my new one again with no luck. So that's where I'm at now. Crazy how it drove fine yesterday then after restart it just doesn't want to do anything.

 

I think you have to click the "Auto-save scan file box" and "Save scan to log file" box. Not sure because I never used Scan9495 to run a data log. I just reviewed the data logs for people.

My Formula was converted to an aftermarket engine management system, that had a scanning/recording system built in. You want to produce the data log file in .csv format. That is something you can add to a post so that people trying to help you can take a look at it. The single frame screen shots like you are posting above don't produce a lot of useful information required for troubleshooting some problems.

 

Today i recorded what the car was doing. Startup seemed fine at first, then it continued to sputter and pop and drop rpms. i included the 2 runs that it did

 

I forgot to add to this that i installed a new Delphi coil on the car before these tests even though the old one ohmed out fine thinking maybe a sloppy connection. When it first turned over it had a code 42 which I cleared and it didn't come back. I was suspecting the plugs being fouled but that wouldn't make sense since it ran perfect the day before. I think right now my main guess right now is the opti or just the cap and rotor on it. Getting that 36 code randomly and these issues maybe the harness is compromised. It's just buried and to unplug from the opti looks to be a pita.

 

Try and access the Opti harness connector. That's the main source of leaks in and out, and there can be corrosion on both sides of the connection the affect the continuity of the wiring. Is the Opti vent system healthy?

 

I'll attempt checking the connector today after work. The vent system is intact and looks fine but I have not run any tests on it I'll look into how to check that.

Thanks

 

Main thing on the vent is that all the components are in place, and the hoses are connected where they are supposed to be. Shoebox covers the physical components:

http://shbox.com/1/opti_vacuum_hose.jpg

http://shbox.com/1/opti_vacuum_harness.jpg

With regard to the harness, check the gray connector on the passenger side of the intake manifold.

http://shbox.com/1/evap_sol.jpg

Also check for damaged wire insulation. The mice enjoy eating it.

 

So checking voltages and resistance at the opti connector at the top of the valve cover everything was there. getting down to the connector on the actually opti was harder, got that out the 12v pin was discolored a bit so i cleaned the connections up tested voltage and resistance and put everything back. Car started right up! idled good, took it for a quick drive and everything felt fine, during the drive i was hearing a slight noise in the engine, got home and grabbed the laptop the knock count was running up to 60ish thousand and then resetting going back down to 0 then back up. Had some timing pulled too. If i gave the car throttle it went away anything above 1500 and the knock count doesn't move. Maybe with all of the poor running and backfiring it caused some damage? or maybe i just need to run it and get it nice and warm and oil moving around. But progress is being made for sure.

Thanks again

 

Went out yesterday to mess with the car. I soldered in a new connector to replace the c230 connector. Buttoned up all wiring under both sides of the dash. Went to drive the car. Took a few seconds to turn over started and sounded good! Ran for about 5 seconds and started to drop rpms did that for a few seconds and died. I went to reseat the optispark connector and the top of the connector broke. I had already ordered another which will be here on Wednesday. My only thoughts now are if the connector doesn't fix it. It's either the discolored pin on the optispark side that I cannot get to since there is no room or the opti is just on its way out after around 10 thousand miles.