So today I was at the parts store getting gasket material to make a carb to spacer gasket for my 82 Honda and when I came out to the truck, it would not start. I'd love to hear what people think could have been the issue and better yet, how to check what the issue could be.

Here are the details:

• Truck had not been driven for 3-4 days before today
• Gas tank full
• Whether dry and nice, 85' F and sunny, low humidity.
• Drove about 2.0 miles from my house to the auto parts store at about 4 pm.
• Was inside for about 10 minutes.
• Came out to start the Blazer and had it crank well with the starter, ignition seemed to occur, but would stop when the key was returned from "Start" to "Run".
• I tried starting it about half dozen times. Sometimes taking the key out and reinserting it to try restarting but only to have the same symptoms.
• I was pretty sure I had ignition and gas due to hearing what sounded like ignition in the cylinders occurring. I was not able to double-check for spark at the coil but I was able to check that there was gas under pressure at the fuel supply line to the engine by pressing on the Schraeder valve and seeing gas come out of the service port.
• After about 10 minutes of trying the cranking, checking the fuel, wiggling the electrical connection to the fuel injectors, even hitting the ignition switch on the steering column with no success, it finally started on its own after a few more attempts.
• I then drove home directly with no issues. I also tried to restart it right after I got home and it started right up.

So, this happened only once before almost exactly a year go, to the week, but at home. Last year, it caused me to cancel a cross the state drive as part of a vacation.

Do any of you have suggestions as to what could be going on to have caused this? What can I check to diagnose possible issues? I'd like to not have this happen when I'm in the woods as even a short drive in can become a long walk out.

Thanks!

 

These intermittent problems are tough because you can’t finish diagnosing the problem in real time. I would travel with a fuel gauge, spark tester and multimeter so that you can try to catch it and at least confirm if it’s spark or fuel. You might also need a remote start capability. Then I would go through the basics quickly while it’s acting up:

Key on fuel pressure and leak down
Spark
12v on the ICM or coil pink wire if no spark
12v on the injector power wires if spark and fuel


After that it gets more complicated with things like injector pulses and timing. Short of that, with no codes or relevant history on suspicious parts, it’s the parts cannon. If that’s the play then I would go with the oldest parts from the trouble maker list: ignition switch, fuel pump, etc.

I feel your pain, I have another vehicle that just won’t stay broke long enough to diagnose so I am going to have to start taking some educated guesses based on the history for that vehicle.


George

 

George,

Thanks for your reply and sympathy.

Right now I need to get my Prelude back on the road, hopefully by the end of today.

I like your suggestions, especially the issues with looking at older parts. The ignition switch was on my suspect list. I had the ignition switch on my Honda go out once too in a similar manner. I have since had a detachable key change for only the three ignition keys I carry to minimize weight on the ignition switch.

BTW, I also found a trouble shooting chart for "Engine Cranks But Does Not Run" that I'm attaching to this post. It suggests a few possible way to have an intermittent failure that I'll also be checking. As for OBD codes, I totally forgot at the time that my Ultra Gauge OBD system I use for monitoring my transmission fluid temperature also can access codes. But I have an iLink I think I'll use later today that can see more than the Ultra Gauge can.

If I figure it out, I'll be sure to post an update.

 

Christine, can't offer with any confidence since your truck is working now, but here are a few thoughts:

1. When you use your scan tool, go into Global OBDII mode (as opposed to GM Enhanced) and take a look at Mode $03 and also Mode $06 for pending codes (first fail). Try to do this within 3 trips as any pending codes may clear. There may be a Pending Code that maybe can help point you in a direction. Look for codes that have a low number of trip or key event cycles. Not sure if your tool has an enhanced mode, but if it does look there for pending codes also. If you don't see pending codes in GM Enhanced, back out, start over and go into Global. May have a different name like "OBD Direct" but it is where you find modes (up to 10). Modes $03 and $06 would be the most helpful. If there is a Pending Code Mode $02 will give the Freeze Frame for the conditions at the time of fault for some data mining.

2. Even though you had fuel pressure at the Schrader, maybe pump built pressure initially and didn't run or didn't run well after that, we don't know how much pressure there was. You didn't mention if you heard pump prime on each of the key cycles (ON & OFF). Two thoughts on this (if you DIDN'T hear pump prime):

a) Pump had a small dead spot and you landed on it when you pulled in. I kind of doubt this one with how rare you have this event and how much you cranked, but we really don't know what the pressure was. Next time you can bang on the bottom of the tank (if you have access to the bottom of it).

b) You have a fuel pump relay issue. You can remove it and look for any carbon tracing or such on the pins. Also look best you can into female terminal of UBEC for any green monsters. It is also possible the internal contacts on the relay are getting burned and you would probably see an increase in the frequency of these events.

c) Along with the diagnostic tools George mentioned, carry a fused jumper wire in the truck to see if you can run pump using the fuel pump prime terminal in the UBEC. Not suggesting you drive like that, but just to see if it will run for a couple seconds. If truck doesn't continue running once you remove the jumper, then I would suspect the relay or associated circuit as the problem.

3. If there is a next time, leave key in RUN position and try to turn on something that is 'Hot in RUN only', like the HVAC blower motor. If the motor doesn't come on, I'd be taking a hard look at the Ignition Switch (once I got the truck home)

4. The fact that after 10 minutes it started could indicate you have high resistance in a circuit (creating heat and causing even higher resistance) and effecting a load at cranking.

5. If there is a next time crank in Clear Flood Mode (pedal to the floor) for about 15 seconds. Then crank like normal (foot off pedal) and see if it starts. I'd have to think harder on why the engine would have flooded. Can't imagine it would be FPR since this such an intermittent issue.

6. Gently wiggle the wires at the CKP sensor.

7. Another one I doubt, but if you get fuel at same place regularly, there's always a possibility of bad fuel (alcohol content to high). Your TSM has a a procedure to test for "Alcohol/Contaminants-In-Fuel Diagnosis" in the "Engine Controls" section. Google and maybe look up on BBB website to see if anyone using that station has complained of bad fuel. Introduction of E-15 and/or Methanol into your tank could cause problems (according to TSBs anyway...never tested it out myself)

I know these are nothing but guesses at this point, but if I was forced to pick something, with only the info we have, I would probably choose either the Ignition Switch/circuit or the CKP Sensor/circuit.

Good Luck!

 

Wow, these are great ideas. I'll.add them to my to-do list.

Thanks so much for taking the time to write them all out.

Christine

 

Quick update.

I finally got a chance to look at my crank but no run situation. I started with plugging in my Vident OBD reader. I was following the trouble shooting from the GM manual. What I was looking for was a fuel cut out for due to the security system, the throttle position sensor being bad, and the temperature sensor being bad. None of these seemed to be the problem. I tried to start the truck but the battery was dead. I hooked up the jump-battery and it started.

I had not moved it since I last posted.

On the GM trouble shooting there was also instructions to test the spark at the spark plugs, the fuel pump operation by measuring the pressure in the supply line, the injectors.

However, I'm thinking what I'm seeing must be some sort of intermittent electrical issue that is central to keeping the engine running. I'm now leaning towards some of the suggestions by RockP2 like a bad relay to explain what I am seeing.

The only other idea I have is if my battery being at the end of its life is somehow to blame for the fuel pump not running. Except for today, the battery would have no trouble cranking the engine so that I assumed that the battery would have had enough voltage and current.

I also need to get a new battery but I don't want to do that until I get this intermittent no-run condition fixed.

I'll keep people posted.

 

Quick update. Although the truck was now starting fine apparently without me doing anything, I did switch the relay for the fuel pump with the one for the lift gate. I figured that the lift-gate one doesn't get used much and if the problem was the relay, it would be a good one to install as opposed to the fuel pump relay that gets used every time the truck is started.

 

Here's another quick update:

I removed what had been the fuel pump relay to open it up and inspect it. What I found was very worn contacts. (see below)

I then did some research to learn how relays fail and their expected lifetime. What I learned is that voltage drops across poor electrical contacts and reduce the voltage at the fuel pump to a point where it will not run. I also learned that the contacts on relays are expected to have a life of about 100,000 cycles. Furthermore I learned that for lamps and motors, the wear and tear on relay contacts can mean having to de-rate the relay by about a factor of five due to the large initial current spikes in these.

A quick back-of-the envelope calculation assuming that for each time the truck is started the fuel pump relay is triggered once to prime the fuel system and then a second time once the motor is started, then assuming one round trip 200 times a year over 24 years, I get a total of (4 cycles/round-trip)*(200 round-trips/year)*(24 years) = 19,200 cycles. This is about a factor of 5 less than the normal life-expectancy.

Now this calculation is pretty crude, but considering the wide error bars involved, it shows to me that it is not unreasonable that a fuel pump relay could be expected to start failing at about 20-25 years.

I have replacement relays for the more critical systems to install. I'm sure GM never expected most of their Blazers to last over 15 years.

https://www.ms-motorservice.com/en/t...check-contact/

 

Once the contacts on relays start "arcing" it becomes progressively worse.

I was helping someone with a fuel injector problem and it was very apparent that they had an issue with either corrosion on the connectors under the UBEC or in the wires themselves due to the symptoms. Sure enough the terminals were corroded. He cleaned them up and all is well. A "no-parts required" fix. His issue was constant so it was a pretty easy diagnosis.

Made me think about the intermittent issue you're dealing with. You might consider unbolting the UBEC and disconnecting the connectors to see how they look. The fuel pump relay involve pins in connectors C1, C2 & C3. Or you could wait until next time it happens so you can know for certain if the fuel pump is coming on or not before you go thru that. Wouldn't want you to risk breaking any brittle connectors, etc if the pump isn't even the issue.

 

Thanks for the ideas. Just to be sure we are on the same page, is the UBEC the under-hood engine compartment fuse block?

BTW, when I pulled the relays the female connectors looked good.