SOLVED: Intermittent Crank No Start (1 Viewer)

Joined
Aug 19, 2019
Messages
45
Location
Atlanta GA
1996, 300K+
Helping a friend and read through search results for "crank no start", great info. Especially Romer's Emergency Troubleshooting Process....pure gold. I've never wished for a vehicle to just die and stay dead, at least long enough to go through the FSM procedures but this rig refuses to stay down for more than a few seconds/minutes.

History: Was chasing random knock sensor codes, forward unit I believe, and after splicing in new connector this issue disappeared. Drove the truck daily for a few weeks and it was running strong and steady. Zero Issues, no codes.

Driving one afternoon engine died and coasted to the side of the road, but restarted immediately. Ran fine. No codes.

Few days later, same thing but wouldn't restart immediately. Crank No Start. Waited 5-10 minutes, fired up ran fine. No codes.

Got it home, next day in the driveway cold start smooth idle. Wiggle Test wire harnesses at: Fuel pump, engine bay, etc, went for drive. Runs fine. Go home park it still at idle at operating temp, go under transmission and start wiggle test on some of the harnesses there. Nothing happens, still idling fine. Crawl out, stand up, turn to look at truck and.....it stumbles slightly and dies. Get in, and it cranks right up and settles in to it's normal smooth idle. We continue with wiggle testing under the ignition switch, all is well. 30 minutes later and it's still idling fine, laughing at us...teasing us....challenging us. Then it throws the knock sensor code we haven't seen for weeks. It was late, we went to bed.

So, being deprived of a any means to systematically diagnose this thing, we looked for any/all grounds, dodgy wires, chaffing, anything that could cause an intermittent electrical fault. When it dies, it sounds like it's running out of fuel, but hard to tell for sure.

Today we are installing a fuel pressure gauge to monitor while driving, next time it fails with any luck we'll see pressure fall off just prior if it's a fuel delivery issue. Fuel pump and Fuel Regulator are relatively new. EGR has been removed and capped. But again, when it runs it runs very, very well with no codes (except knock sensor code). It does only happen after engine is up to full operating temperature, never when cold or even warm so could be heat related.

Normally I don't through parts at vehicles, but I'm willing to make exceptions with intermittent electrical if within reason. Any suggestions on which components to replace blindly or other places to look for specific wiring degradation issues.
Thanks all, S.
 

ppc

M Go Blue
Joined
Aug 18, 2003
Messages
3,371
Location
Nashville, TN
If you have not done so already the first thing to replace are the fusible links. Cheap ($15) and the heart of the electrical system and should be treated as a maintenance item.

In your description of the no start problem you haven't specifically indicated if with the ignition turned on before starting that the CEL dash light is on indicating the ECM is powered on and ready to start.
 
Joined
Aug 19, 2019
Messages
45
Location
Atlanta GA
Thank you for the response. Yes, other than the knock sensor, no anomalies. CEL illuminates as it should, however we will make sure on next episode just to confirm. If we can get an extended crank no start condition. So fusible links can fail intermittently? Good to know and easy cheap part to toss in the pit. We’ll do that.
 
Joined
Aug 19, 2019
Messages
45
Location
Atlanta GA
Confirmed, CEL was lit with key on the last time it failed to start. ECU is apparently powering up correctly. We are ordering fusible links in the morning, in the meantime cleaning/burnishing fuel pump relay.
 
Joined
Aug 19, 2019
Messages
45
Location
Atlanta GA
Fusible link is in now, and so far no issues but we'll need a few miles. There was NO fusible link in the truck, previous ownership deemed it unnecessary apparently an had removed it an wired directly to battery. Meanwhile, we are still fighting knock sensor code on bank one. Soldered in a new pig tail (again), heat shrink, wrapped and secured the harness.........less than 1/2 mile down the road it throws the code.

I've never had a vehicle so demonic in it's randomness, we have swapped knock sensors (bank 1, bank 2) and the code stays on bank 1, we returned the sensors to their original position. The pig tail is the second part and third solder, this time we are confident the solder joint and pig tail are solid. On the shelf we have new in the box knock sensor, crank position sensor, and main relay to try. Any other places to look for this random knock code would be greatly appreciated, it's killing us.
Thanks, S.
 
Joined
Aug 19, 2019
Messages
45
Location
Atlanta GA
Update: New knock sensor was installed prior to most recent incident.

So to recap:
Issue:
  • Random Knock Sensor Code, Bank One
Attempts:
  • Swapped Bank One and Bank Two sensors, no change (returned to original positions).
  • New pig tail installed, no change.
  • New knock sensor installed, no change.
  • New fusible link installed, no change.
Other:
Intermittent crank no start, has not returned since new fusible link install (fingers crossed)
 
Joined
Aug 19, 2019
Messages
45
Location
Atlanta GA
SOLVED.
For future searches: Pull the glove box and confirm ECU is solidly mounted and connector fully engaged, might be worth unplug/plug in connector once for good measure. If you have contact cleaner take this opportunity to give both a good cleaning.

Symptoms:
Intermittent crank no-start and knock sensor code bank one. Driving along fine, and it dies and drift to the shoulder, crank no-start. Wait a few minutes and it starts. Knock code is always coming and going with no relationship to crank no-start, at least as far as frequency/duration is concerned. Rough roads and large bumps seem to trigger the no-start, but not always. Knock sensor code completely unrelated to road conditions.

Due to intermittent nature, diagnosis was difficult but when it was starting/running normally:
  • Fuel pump and fuel pressure checked good. Fuel pump and filter are fairly new.
  • Spark checked good.
  • Wire wiggle test: Fuel pump, under intake manifold, back of head up to firewall. All good.
  • Wire harness at EGR and firewall grommet look good.
  • Bank One/Two knock sensors swapped, no change.
Parts replaced:
  • knock sensor pigtail
  • knock sensor
  • crank position sensor
  • fusible link (previous owner had removed and wired directly to battery)
SOLUTION:
We decided to consider a bad ECU or wiring to/from the ECU. Glove box out and you get a good view of ECU....in our case it was hanging by the harness...NOT bolted to anything save one very loose fastener. To make matters worse, what I believe is the stereo amplifier, sharing the bracket with the ECU. The weight of both pulling the harness from firewall grommet. Bolted up and hit the local road under construction at speed, chassis dancing all over the place.....rock solid, no knock code truck ran strong. Unbolt ECU returning it to it's dangle, same road, same speed....truck dies at first bump. One more cycle and we are happy to say it seems the extra stress at the ECU connector was the root of our issues. No wires where chaffed at the firewall grommet or connector. All pins look fully engaged as well. We need some miles to be sure but I'm calling it for now. Thank you all.
 

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