Cranks, no start

[charliekwin]

My 78 was starting and running...until yesterday. I just passed smog on Friday afternoon, but have an occasional misfire and slightly high idle that I was trying to track down. I took off the AAR, and when I tried to start the car again it cranks, but won't start. Not even a sputter. So far I have:

Pulled the plugs; they look good

Checked for spark at one of the plugs; that also looked good.

Ran the voltage and continuity checks at the ECU connector; also good.

Fusible links are good.

Fuel pump runs. I haven't checked the pressure yet. But:

This morning I shot starting fluid into the manifold. Did nothing at all. That makes me think the problem is spark, but I have a spark when the plug is out and grounded.

Any suggestions on where to go from here?

ETA: I just pulled out all plugs again and a couple are a bit wet now. Going to leave them out and let everything sit for a while to dry out and see if that helps.

Edited January 27, 2019 by charliekwin

[240260280]

I had intermittent on ignition switch.  It would not start when turned all the way (100%) to the mechanical stop when starting. If I only turned it ~80% of the way it would start. I guess the contact wiper was carboned-up at 100% but not at ~80%.

[Zed Head]

1 hour ago, charliekwin said:

Any suggestions on where to go from here?

ETA: I just pulled out all plugs again and a couple are a bit wet now. Going to leave them out and let everything sit for a while to dry out and see if that helps.

You might check your coolant temperature sensor circuit.  There are two bullet connectors in the harness in the vicinity of the AAR.  If it gets disconnected the ECU will think you're in the Arctic, or Minnesota today, and add tons of extra fuel.

[charliekwin]

An update/renewed call for help.

• Earlier in the week, after letting things sit for a couple days without the plugs, on the first crank it tried --very briefly-- to fire one time. That was it, then back to cranking only.
• The resistance on the coolant temp sensor circuit is right where it should be. I have a potentiometer wired in, and it's set to zero.
• This afternoon I put a pressure gauge back in. I don't have the right sized hoses, but it read about 30 PSI before it started to leak, so I don't think that's my problem.
• I could also hear injectors clicking when my wife cranked it.
• Bought a new set of plugs today. After installing those, it did the same thing as earlier in the week: tried to fire once on the first crank, then nothing.

Haven't had any real hard-start or no-start problems before; all this came after taking off the AAR and heating plate under it. I've tried putting them back too (excluding the coolant lines on the plate), but it doesn't make a difference.

[Zed Head]

18 minutes ago, charliekwin said:

• The resistance on the coolant temp sensor circuit is right where it should be. I have a potentiometer wired in, and it's set to zero.
•  
• Bought a new set of plugs today. After installing those, it did the same thing as earlier in the week: tried to fire once on the first crank, then nothing.

Were the old plugs wet when you took them out?  Or dry?  And did you measure sensor resistance at the ECU connector?  You said that you have up above but you didn't say specifically here.

You haven't really confirmed good spark either.  I had weak spark once that looked decent but wouldn't start the engine.  My bad ignition module would start with starting fluid but not with gasoline.  Did you use real starting fluid or some other fluid like carb cleaner?  Starting fluid is pretty potent if spark is present.  If you have spark and dry plugs you should get a few pops with starting fluid.  You could wire up a GM HEI module pretty quick for about $25.  A fairly inexpensive test, and then you'll have a spare.

If all else fails the last suggestion is another ECU, according to the FSM.  What you're describing is typical of how ECU's fail.  

One last thought is bad gasoline.  

 

[charliekwin]

A couple of the plugs were wet earlier in the week, others dry. The new ones are dry, but I only tried cranking a couple times. Plenty of gas smell in the garage too, FWIW. (I doubt the gas is bad; I filled up after getting the car back on the road a couple weeks back.)

Resistance measured at the ECU connector, yes. The other EFI bible checks were good, but that doesn't mean the ECU isn't bad. Are there any tests that can be performed on the ECU itself? It's hard for me to imagine that I did something to kill it dead by removing the AAR, but I'm not in a position to be ignoring possibilities right now.

Used real starting fluid, didn't get even a pop out of it. I'll be honest, I'm not really sure what the spark should look like, so I'll shoot a video this weekend. 

[Zed Head]

1978 has the "high energy" ignition system so you should get a strong blue spark.  I damaged my GM HEI module by leaving two spark plugs disconnected by accident and starting the engine.  Ignition modules are kind of sensitive.  Yours is old too.

Any chance you've created a big vacuum leak by accident?  Damaged the hose from the AFM or knocked off a PCV hose?  That would lean things out a lot.  All hoses must be intact.

[Dave WM]

You need to get an exact fuel pressure reading. disconnect the small wire from the starter solenoid, engine will not crank but pump will come on. Should be 36 psi. One step at a time.

[charliekwin]

Well. My fuel pump just puked gas all over the floor. Guess I'll deal with that first, once the weather improves.

[Dave WM]

the details of what happened may help with the diagnosis of the original issue. Generally speaking you want to go thru all the major systems, make sure wear items are dealt with considering age.

ALL rubber lines (fuel/vacuum) are way past due if original to car.

Electrical, suspect every connection  and ground. check and refurb as needed. This includes rubber covers etc.. need to keep moisture out.

Battery, often overlooked, good cables (not clamp on quick fix, think OE style).

fuse links and connections to same, make sure in good condition, better still replace with new fuse links and make sure all blade type connectors are in good clean condition.

Grounds, make sure ALL grounds (there are a lot) are solid and contact clean metal. look for "green wire corrosion" you will see it creep up copper wires. if it there you must cut back to good copper and make solid repairs.

It would be best to address one of the above with a working car, but if you have a situation where you have tried the FSM trouble shooting procedures, then the above may solve an issue that the FSM was not written to address (like a 40+ year old car with wiring and other age related problems).

The reason being you "could" introduce a new problem by a botched repair attempt. Multiple failures are rare on there own, but easy to introduce by addressing multiple systems with no way to confirm if they worked after the repair. An example, replacing fuel injector harness connections making poor connections resulting in a non functioning injector where as before it worked but was just ratty of the plastic parts were falling apart. A few of those, and a botched ground fix etc... could result in a major hassle in trying to find them in a non working car. Can't say it enough, its almost always going to be a single point of failure that stops a running car, so diagnosis is the way to go vs shot gun repairs of multiple systems.

 

 

Edited February 3, 2019 by Dave WM

[charliekwin]

Thanks Dave, that's all good advice. While I've replaced some things in the past (2-3 years ago, before doing body and paint) that either looked especially dodgy or gave out on me, I was lucky enough to buy a car that's always started and run reliably. Right until I pulled off the AAR last week, anyway. That point of failure is what I'm trying to find. It might not be related to the AAR, but the timing is hard to overlook. The new fuel pump leak might (or might not -- it was no-starting for a week before the leak) be related to the no-start issue, but I obviously can't look at anything until I fix it.

[Dave WM]

That AAR  just does not seem possible to be a problem, unless its not open and there is not enough air bleeding thru. If you remove it, too much air bypassing the throttle, would make for way high idle.

Just keep at it. Right to get the fuel leak fixed (obviously you don't want a fire). Looks like you will just have to double check the reg stuff. I agree, its hard to overlook the timing, but sure does not seem like the AAR could cause you so much problem.