1993 LT1 Intermittent Crank-No Start

[Mark E.]

Two weeks ago, I drove my new-to-me 1993 (now with 19,000 miles!) six miles to a 7AM meeting at a nearby Hilton Garden Inn. It was running great in the sunny 30 degree weather. But after the meeting an hour later, it cranked but would not start.

Although my new Chinese fuel sending unit showed empty for the past 10 miles, I was confident I had at least 7 gallons in the tank (it goes to one bar reserve with 8 gallons of fuel left). Even so, I had AAA add 3 gallons just to be sure.

It still cranked but would not start...

Because I didn't recall hearing the fuel pump the first time it cranked, I asked my bride to deliver a spare sending unit/fuel pump assembly I had in the garage along with the handful of tools needed for its R&R. An hour later the sending unit/fuel pump was replaced. When the key was turned to "on", I heard the reassuring whir of the pump for a couple of seconds... I was confident it would start.

But no! It cranked but would not start...

It's now 10AM and the temperature dropped 15 degrees as the winds of a cold front moved in. Time for a tow truck. (Getting a tow truck with a skilled operator willing to follow towing instructions took 24 hours and three attempts... a rant for another time.)

Today it finally warmed back up (70 degrees!) so I began the diagnosis. Following the "Crank-No-Start" flow chart in the service manual:

- I checked for codes (none)

- I attached a fuel pressure gauge to the fuel rail and a spark tester in-line with the #4 plug wire (the easiest to access). The idea was to check for fuel and spark while cranking.

Guess what? It started immediately. That's the good news; the bad news is I now have an intermittent start problem.

Any ideas?

[Keith B.]

Re: 1993 LT1 Intermittent Crank-No Start

was the fuel pressure within spec? and by cranking you can hear the starter turning over? if not the vats will shut down the starter for, I think ten mins

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Thanks Keith and Dave!

Fuel pressure was low 40s (I think 42-44) which I believe is normal. It held for 30 minutes until I disconnected the gauge.

I only checked the ECM codes. I will also check the CCM codes and report back. (Crossing my fingers it's not the ECM, but definitely want to run down this intermittent failure.)


P.S. I just looked at SIA's website. Not a cheap service but it's good to know there's a resource out there that repairs these ECMs.

[Edward J.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark, I have seen a few problems with coil wire corroding inside the tower of the cap or the coil, worth a look, next with car running wiggle test the wire harness connectors on the opti spark,and coil.look at the water pump weep hole for anti leak, I have seen the anti freeze leak onto the Distributor and make it way internally and cause issues, but generally will also cause misfires when running. Another issue is The computer circuit board will cause intermittent no starts as mentioned sometime can tap the metal box with your knuckle and see if the engine stumbles.

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

I went into the diagnostic mode of the CCM today. Automatic mode showed only one code in Module 1 (CCM), C12, which means "No DTCs". Module 4 (ECM) and Module 9 (ABS/ASR) had no codes. To be sure, I checked codes in manual mode too... no DTCs.

Coil wire terminal looks clean.

I was hoping to find something to explain the intermittent crank-no start. The car is running great but I'm avoiding shutting it down anywhere but home.

Ideas?

[Justin S.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark,
You can write this off as ignorance because I know nothing about C4s. Have you looked at the ignition switch? Were these fly by wire?

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark,
You can write this off as ignorance because I know nothing about C4s. Have you looked at the ignition switch? Were these fly by wire?

Engine cranks and ignition has spark so the ignition switch is doing its job. But I need to test spark and fuel pressure when it doesn't start.

C4 uses an old school throttle cable.

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Happy New Year folks!

An update about the intermittent crank-no start condition. The car has been running and starting normally since 12/28 (4 days). Trying to recreate the problem, I start it, shutdown and repeat; I start it, drive for a couple of minutes, go home, shutdown, restart it; I start it, drive for 20-30 miles, go home, shutdown, restart it; I restart it immediately after shutdown; I restart it an hour after shutdown; I wiggle the cables to the ECM then start it.

With this unresolved issue, my thought is to carry a fuel pressure gauge and spark tester then wait for the problem to happen again. And of course, keep my AAA membership.

[Edward J.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark, I think I would leave fuel pressure gauge on car, as long as it has a good seal on pressure fitting, and spark tester in line. So if it happens you can see what’s going on. Another thing I have seen in my years repairing cars is GM cars the coolant temp. Sensor going into a open situation and when looking at a scan tool data the sensor reads -41 degrees. This will not let the car start or hard start when the car is hot. And may or may not set a code. The car will have normal fuel pressure and spark. Also the coolant sensor can leak a very small amount of coolant in the electrical pins and cause corrosion.another thought is the chip on the key for anti theft system can sometimes not be read due to oil from your hand building up over the years, some contact cleaner on a rag will clean it, I don’t have a service manual but some of the systems will shut down for a few minutes when this happens.

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Thanks Edward.

Interesting tip about leaving the fuel pressure gauge and spark tester attached.

I assume you're talking about the temperature sensor for the ECM that's on the front of the engine...

I think VATS is okay because the car always cranks.

Best,

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

It happened again...

Exactly four weeks after the first crank-no start it happened again in the same scenario: Leaving the same Wednesday morning meeting, same time, same hotel parking lot, but about 20 degrees warmer. No codes (checked both the ECM and CCM codes in the parking lot), wiggled the cables to the ECM, ignition coil and module, even rocked the car. No luck. I didn't hear the fuel pump so I pressed the valve on the fuel rail and gas dribbled out. I expected it to be under pressure so maybe this is a problem? After this check I turned on the ignition but didn't hear the fuel pump which I thought was surprising.

The tow truck just delivered the car to our house. I'll check for spark and fuel pressure a bit later.

This happened after weeks of intentionally starting, stopping, again starting the engine after multiple short trips with no failures.

If spark and fuel pressure check out (like last time), and if you guys don't have any better ideas, it may be time for an experienced OBD 1 GM mechanic to trace this down.

The car is fantastic except for this serious issue... we'll figure it out.

[Edward J.]

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark, I don’t have a shop manual, and it’s been awhile since I have seen this, does the key with the chip in 93 disable the fuel and starter?

Edward,

VATS disables the starter (and probably fuel too). Since the engine cranks, I've ruled out VATS as the problem.

[Edward J.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark did you install a pressure gauge to see if it here was fuel pressure? Generally when you push down on the test port for fuel rail there should be a good squirt of fuel. Or did car start again.

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark did you install a pressure gauge to see if it here was fuel pressure? Generally when you push down on the test port for fuel rail there should be a good squirt of fuel. Or did car start again.

Edward,

I also expected greater fuel pressure than a dribble. I didn't attach the fuel pressure gauge while driving (as someone earlier suggested) because I was concerned about causing a leak. But in the next day or two, I'll check pressure and spark and report back. I'm actually hoping it won't start like nothing is wrong so I have a chance to figure this out.