77 280 cold start vs main injectors

[rosaluma]

After 18 months of father/son restoration, we are finally looking to get this thing running.  Took it all the way down to rolling chassis, we rebuilt the engine, rings, bearings, timing sprokets, chains, valve seals.  Put it all back together, with new coil, cap, rotor, wires, plugs, injectors, fuel pump, filter.  Car will start, but not fire.  Plenty of good spark to each plug.  36 psi fuel pressure to the rail. Used both the factory service manual and fuel injection bible troubleshooting guide. Traced it down to the injectors not receiving signal to fire. However, the cold start valve does.  How is this possible?  We've worn the battery down, and recharge it, each session that we attempt to troubleshoot.  Is it possible for low voltate, 11.8, to prevent the injectors from firing?  Are both the cold start injector and the main six injectors on the same relay?  Bad relay?  Upon inspection, the relay looks fine.

[Zed Head]

Car will start, but not fire. 

 

Traced it down to the injectors not receiving signal to fire. However, the cold start valve does.  How is this possible? 

The cold start injector opens when the key is turned to Start.  The cylinder injectors open when the ECU grounds them after receiving the signal from the blue wire at the coil negative terminal.

 

For most of us, "fire" and "start" are the same thing.  So "will start, but not fire" doesn't make sense.  Maybe you mean that it will start but not stay running?  That might be the fuel pump contact in the AFM.  It's bypassed at Start but comes in to play on Run.  If it opens, the fuel pump will lose power and the engine will only run for a few seconds.

 

Or maybe you mean it will start with starting fluid but won't stay running.  That would be an injection problem.

 

What year car?  Not all have the AFM fuel pump switch.

[S30Driver]

When you went thru the troubleshooting, did the test between the coil negative terminal & pin 1 of the ecu connector shown good continuity?  This is the all important pulse signal that fires the injectors.

 

When you rebuilt the car, did you make any changes, upgrades or modifications to the ignition system, etc.?  What year is the car, from the hood looks like 77 or 78?  (oops, just re-read the title - 77)

Edited December 7, 2015 by S30Driver

[rosaluma]

Thanks for the quick replies.  Yes, continuity between coil negative & pin 1 per the bible.  No modifications to the 77 during restoration.  Yes, cold start kicks in when key is start.  However, injectors are not getting a signal.  I plugged in a test light to the harness at each injector...no light.  But, when I plug in the same light to the cold start, it lights up.

 

Zed, it will not start, even with starter fluid.

 

Just charged the battery back to good....red herring. 

 

HLS30-350228

Edited December 7, 2015 by rosaluma

[Zed Head]

So it will "crank" but not fire.  It should still start though, for a few revolutions, from cold start fuel.  Bad gas, maybe?

 

Way back, a friend and I spent some time trying to get an old 1963 Bonneville to start after sitting for just one year.  It just wouldn't fire even though we could see and smell the fuel in the carburetor throat.  A farmer happened by on his tractor and told us to squirt some oil in the spark plug holes, the cylinders were probably dry.  A few squirts in each hole and it fired right up.  Ran great.

 

Anyway, short version, a new engine might not have the rings sealing well.  Try some oil in the cylinders.  It will burn off.  

 

Or some starter fluid.  The starter fluid will tell you if the timing, both cam and igntion, is right and if the engine will even run if it gets fuel.

[Patcon]

I believe he has it fixed. Low battery...

[Zed Head]

Thanks.  I missed that last part.  And the part about starter fluid.  Odd though, that strong spark was observed.

[rosaluma]

Wish it were true, Patcon, but alas...no start. Will research the AFM.

Edited December 7, 2015 by rosaluma

[Zed Head]

 

Just charged the battery back to good....red herring. 

 

Red herring meaning you thought the low battery was the problem.  Alrighty.

 

You're on the edge of following random things without knowing the sequence of events that happens when you turn the key.  If the AFM switch is misadjusted or has dirty contacts, the engine will start and run for a few seconds, until fuel pressure drops.  The engine should also try to start, combustion events while cranking, from the cold start valve fuel.

 

And, finally, most importantly, you said that you have strong spark.  So it should definitely start with starting fluid.  

 

You might have a timing problem or some other odd problem like valves not opening.  I would run through the basics.  Measure cylinder pressure if you can, make sure the valves are opening and closing.  Make sure spark is happening on the compression stroke and not the exhaust stroke.  The ignition timing mark is in the right spot twice.  Check the weird things that happen when people put their engines back together.  Spark and starting fluid should at least get a few spins from "fire".

[rosaluma]

Compression is 110, 90, 125, 110, 110, 110. Found TDC and checked/reset the destributor multiple times, to be sure.

[gwri8]

SteveJ humbled me when we had a similar problem with redwing.  I had pulled the distributor and when I had replaced it, it was 180 degrees out. Something very simple to check.

[rosaluma]

Thanks, gwri8.  I've checked it, and rechecked it a couple of times.  Found when 1 is at TDC, pulled distributor, reset, etc.  Still no fire.  I believe Zed is onto something with AFM.  Will check this tomorrow.  Here is what I found in other forums...

 

The fuel pump control for the 75 - 77 N/A.

When the engine is not running the flap in the AFM is closed and the fuel pump control switch in the AFM is OPEN. When the key is turned from "OFF" to "RUN" there is no continuity through the fuel pump switch in the AFM and the fuel pump should not run. When the key is turned to "START" the engine turns over AND the fuel pump relay closes which starts the fuel pump. As air is sucked past the flap in the AFM it opens and the FUEL PUMP contacts in the AFM close. When the engine starts the air flow through the AFM keeps the fuel pump running because the switch is closed. If the engine stops / stalls the flap in the AFM closes and the fuel pump control switch in the AFM opens thereby shutting off the fuel pump.

 

Still doesn't explain why the injectors are not receiving any signal from the ECU but, as you can tell, I am chasing anything. 

 

I truly appreciate all of your input.  I make no bones that I am not very qualified, as a mechanic.  Just very eager to have my son proudly driving his first car, very soon.  

Edited December 7, 2015 by rosaluma