10 replies to this topic

[Maniac motorsports12]

I have a 1992 SM that has not been started in almost a year.  When I went to start it, it would fire, run smooth for 15 sec and then stall.  The longer I played with it the less it would fire.  Used some starting fluid and it would fire, run for a couple seconds and shut down. 

Here is what I did:

Pumped all the old fuel out of it.  Made sure the fuel pump was working.  put 5 gallons of fresh fuel in

Changed the fuel filter

put a new battery in 

no change

 

Any ideas?

Thanks

Mike

 

[callumhay]

If the car was stored outside , check the vane on the air intake box as it might have stuck partially closed...use some WD 40 on it to loosen it up. I'd work on from there if its not that...air, fuel, spark. Check connections, sensors, look for vacuum leaks, grounds loose, etc .
Cal

[Steve Scheifler]

Did you confirm that the pump actually holds pressure as it flows?

You might get a quick answer from someone but these things often end up being a series of questions with each answer narrowing the likely list.

What do the dash lights and gauges show before it dies?

Does it die smoothly? (All stop pretty much at once and quietly?)

After complete cool down does the cycle repeat with it running longer, then shorter each time?

Does it get to the point where it won’t fire at all without starter fluid?

What do the plugs look like?

What does the exhaust smell like?

Have you removed & replaced the big connectors to the air flow meter and ECU (contact corrosion can be an issue and get hot. Though I put this one low on the list with your symptoms it’s something to do occasionally and especially after sitting a long time.)

[Ron Alan]

Had a similar situation and symptoms. Narrowed it down to no fuel...no injector pulse! Mine was an early 1.8 that gets its injector pulse from the coil(ground pulse). Changed coil and it fired right up and never looked back. Not sure if the injector pulse for the 1.6 follows the same path?

[Bench Racer]

Install a fuel pressure gauge with a long hose so you can view gauge when starting/running/racing to confirm constant pressure. I have a T in the input line with a  hose traveling to a second T. At the second T is the fuel sample port and a hose traveling to the cowl outside the windshield with a pressure gauge. 

[MPR22]

I have a 1992 SM that has not been started in almost a year.  When I went to start it, it would fire, run smooth for 15 sec and then stall.  The longer I played with it the less it would fire.  Used some starting fluid and it would fire, run for a couple seconds and shut down. 

Here is what I did:

Pumped all the old fuel out of it.  Made sure the fuel pump was working.  put 5 gallons of fresh fuel in

Changed the fuel filter

put a new battery in 

no change

 

Any ideas?

Thanks

Mike

I am 90% sure your AFM is failing.  Usual problem is stuck flapper or the wires are not connected well.  

[Tom Hampton]

I am 90% sure your AFM is failing. Usual problem is stuck flapper or the wires are not connected well.

Agreed. Those wires run from the ecu across the dash to the drivers side. Then the go through the firewall and out to the afm. It's probably either the airflow signal or the temperature signal wire. Both are thicker, shielded wires. Don't remember the color codes off the top of my head.

I'd also bet that if you disconnect the battery and reconnect...it will fire once, the die...and then won't fire again until you disconnect the battery.

[Steve Scheifler]

His description is that it ran smoothly for 15 seconds then stalled. After that it kept starting but ran for less time each round. More details and a repeat from cold are necessary but based on those facts I can’t explain it with a simple mechanical flapper issue. Not that I’m betting against it, I may be reading too much into the intial description, it just isn’t my first guess. It sounds more like something overheating electrically. Maybe the coils (unlikely both sides in concert) or the injection module (or feed to it as suggested by Ron), or even connectors. But as described it sounds like a single failure point hitting all four cylinders like a light switch and progressively sooner with each attempt. Like something is heating up. All assuming that can be repeated from cold, which we don’t know, but that should narrow the possibilities a lot. If it’s completely dead now then that’s also an important clue. IF in either case the starter fuid continues to work even after it otherwise won’t start at all that narrows it even more, but that hasn’t been confirmed.

It’s always fun and tempting to guess but a few basic troubleshooting steps can zero in on it pretty fast.

[Steve Scheifler]

Memory flashback! I will contradict my own statements about the flapper. Somewhere I have a “new” reman AFM which from the first time I tried it acted similar to your scenario. It took longer before stalling but as soon as it started to physically warm up something warped or twisted slightly causing the flapper to drag on the housing and stick. Not always fully closed, but generally close, and it could got to the point where even significant force with my finger didn’t budge it. It doesn’t sound like yours ran long enough to physically warm the housing, and once stuck in a position it should either start and run or not, but there are similarities. I’ll still put my chips on a different answer but with much less conviction pending more details.

[Tom Hampton]

My understanding of 1.6 engine controls:

 

1.  ECU requires air flow input from AFM.

2.  ECU requires air temp input from AFM.

3.  ECU requires WOT switch input from throttle body.

4.  ECU requires crank angle input from the CAS in the back of the cylinder head.

 

If ECU does not sense these inputs within normal operating ranges within ~3 seconds of initial start, then it will kill the ignition pulses to the coil.  The ECU will then log this failure in internal volatile memory.  The ECU will refuse to send ignition pulses while this failure is logged.  I am not clear if there is a timeout on this failure, as I haven't tested it rigorously enough to be able to tell.  Removing unswitched power from the ECU clears this logged failure---at which point the ECU will again attempt to start the engine, and the cycle repeats. 

 

AFM has a reed switch that is in series with the fuel-pump ground.  If the flapper door is fully closed the reed switch will prevent fuel pump from flowing.  If you take the cover off the AFM there is a little metal arm that opens/closes the reed switch, this can be bent out of the way to prevent it from ever shutting off the FP. NOTE: Losing fuel PUMP will not result in an instantaneous engine shut-off.  Only once fuel pressure bleeds will engine sputter and die.  I went through this exact failure mode at Hallett back in June.  At idle, it takes quite a long time to bleed pressure away.   Even at WOT, the engine leans out and sags in power...but, doesn't "die" instantly. 

 

The fuel injectors are powered by switched power directly from the main relay.  The ECU injector "pulse" grounds each injector to energize the solenoids in pairs (1,3) or (2, 4).  There is nothing else involved electrically in the 1.6 injectors (different from the 1.8 described by Ron above). 

 

The ignition coils receive ignition pulses from the igniter, similar to the fuel injectors, these are also in pairs (1,3) and (2, 4).  These pulses are again GROUNDing of the coil.  The coils are energized by switched power from the ignition switch.  There is a capacitor across the coil, which is critical for proper ignition operation.  The igniter receives pulses directly from the ECU.

 

If you need NA scematics, you can find them in the downloads section of my "build" link below. 

 

I stand by my theory above, that it is likely a sensor input to the ECU failure (broken wire, failed sensor, etc).  To (dis)prove this, disconnect the battery for a few seconds, and then reconnect and start the car.  If you get a short "run time", followed by none...every time you disconnect the battery, then you have a bad sensor input, 1-4 listed above). 

 

If its not the ECU shutting off the ignition, then my next most likely culprit would be the igniter....its really the only other component that is COMMON to all 4 cylinders (or really the two cylinder pairs). 

 

After that, it could be the condenser capacitor that is across the coil power.  A bad capacitor could initially hold a charge, but then progressively fail to maintain that charge eventually resulting in a loss of spark.  This COULD manifest itself in a semi-random run-time depending on the time between attempts, and any progressive failure mode of the capacitor materials. 

[Tom Hampton]

You can also try reading the diagnostic codes from the ECU. 
 
1.  Recreate the failure.
2.  turn off key.
3.  Jumper the TEN terminal (diagnostic port) to GND.
4.  Turn ign key to ON (do not start).
5.  Check engine light will flash diagnostic codes.  slow flash = tens digit, 1.6 second pause, fast flash = ones digit, 4 second pause, next code.
6.  Codes are flashed from lowest to highest numerical value.  Once cycle repeats you can stop.

1 Ignition pulse (No Igf signal)
2 No Ne signal
3 No G signal
8 Airflow meter open or short circuit
9 Water thermistor open or short circuit
10 Intake air thermistor in airflow meter open or short circuit
12 Throttle position sensor open or short circuit
14 Atmospheric pressure sensor open or short circuit
15 Oxygen sensor <0.55 V 180 sec after 1500 rpm
17 Oxygen sensor unchanged after 1500 rpm
26 Solenoid valve (Evaporative canister purge)
34 ISC Valve