Help! - No Fire Situation - PCM does what?
07-23-2014, 11:18 AM
#1
Intermediate
Thread Starter
Member Since: Jul 2006
Location: McCalla Alabama
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
Help! - No Fire Situation - PCM does what?
Greetings!
Really need some help. A little over my head on this.
Daily driver 94 coupe which I use for work and back, about 35 miles each way. Need this thing running.
Have been chasing an intermittent "shut off" & "no fire" situation. There has been no pattern. About once a day it just shuts off while driving with no warning. Like key being shut off. Or after stopping for 1/2 hour or so, it will not fire. 1/2 hour more and it fires up an runs like a scalded dog. It is hard to confirm what is not working because it is all working when I get it where I can confirm fuel or ignition. Mounted fuel gauge on windshield to help monitor. Fuel is to rail typically. So chasing electrical. NO CODES!
Have tried to chase the main culprits. Ignition switch was changed. Fuel pump was original so changed it. Filter changed. New ICM & coil. Opti & wires are less than 1 year old after 19 years on original. No water leakage on new pump which was installed at same time.
During last "no start" I noticed on the Fuel gauge that after the 2 second "pump on" at start up, the pressure continues dropping no matter how long I crank the motor. (Will chase check valve on pump or Injectors leaking after I get this "no fire" situation solved.) This seems to indicate that PCM is not believing motor is cranking/running and is not sending fuel pump on or a firing order to ignition. Have tried the tap on PCM trip and it does not stutter or die.
My questions...
1. Does oil pressure/fuel switch not reporting adequate oil pressure to PCM, cause PCM to not send firing instructions to the ignition AND turning on power to the fuel pump? Both or one or the other???
2. What sensors or conditions would cause PCM not to send fuel pump on firing instructions to the ignition system?
3. Is there a simple way to check the optical sensor in the opti without taking it all apart?
Thanks so much for any suggestions or help.
Really need some help. A little over my head on this.
Daily driver 94 coupe which I use for work and back, about 35 miles each way. Need this thing running.
Have been chasing an intermittent "shut off" & "no fire" situation. There has been no pattern. About once a day it just shuts off while driving with no warning. Like key being shut off. Or after stopping for 1/2 hour or so, it will not fire. 1/2 hour more and it fires up an runs like a scalded dog. It is hard to confirm what is not working because it is all working when I get it where I can confirm fuel or ignition. Mounted fuel gauge on windshield to help monitor. Fuel is to rail typically. So chasing electrical. NO CODES!
Have tried to chase the main culprits. Ignition switch was changed. Fuel pump was original so changed it. Filter changed. New ICM & coil. Opti & wires are less than 1 year old after 19 years on original. No water leakage on new pump which was installed at same time.
During last "no start" I noticed on the Fuel gauge that after the 2 second "pump on" at start up, the pressure continues dropping no matter how long I crank the motor. (Will chase check valve on pump or Injectors leaking after I get this "no fire" situation solved.) This seems to indicate that PCM is not believing motor is cranking/running and is not sending fuel pump on or a firing order to ignition. Have tried the tap on PCM trip and it does not stutter or die.
My questions...
1. Does oil pressure/fuel switch not reporting adequate oil pressure to PCM, cause PCM to not send firing instructions to the ignition AND turning on power to the fuel pump? Both or one or the other???
2. What sensors or conditions would cause PCM not to send fuel pump on firing instructions to the ignition system?
3. Is there a simple way to check the optical sensor in the opti without taking it all apart?
Thanks so much for any suggestions or help.
07-23-2014, 03:17 PM
#2
Team Owner
1. No.
2. None that I can think of.
3. It would throw a code if it was that bunged up.
Now... a few thoughts...
1. Check the battery and associated connections. Make sure everything is good and tight.
2. Does "SYS" ever flash on the speedometer?
3. Behind the battery is a power junction block, make sure it's clean and all is tight.
My guess? Recheck the ICM connections. A friend had a huge problem just like yours, and it was caused by a faulty/worn out ICM harness. The female sockets on the harness wear out over time and get loose, the plastic gets wonky with wear, also. Make sure, if nothing else, that the harness is clean and the female sockets are pinched snug, so the male pins won't miss their contact.
I apologize in advance for the sexual nature of the statement above, but I was having a problem finding better wording.
2. None that I can think of.
3. It would throw a code if it was that bunged up.
Now... a few thoughts...
1. Check the battery and associated connections. Make sure everything is good and tight.
2. Does "SYS" ever flash on the speedometer?
3. Behind the battery is a power junction block, make sure it's clean and all is tight.
My guess? Recheck the ICM connections. A friend had a huge problem just like yours, and it was caused by a faulty/worn out ICM harness. The female sockets on the harness wear out over time and get loose, the plastic gets wonky with wear, also. Make sure, if nothing else, that the harness is clean and the female sockets are pinched snug, so the male pins won't miss their contact.
I apologize in advance for the sexual nature of the statement above, but I was having a problem finding better wording.