77 dies while running

[n2deep]

Hi Guys,

I rebuilt/restored my 77 in 2002. The car will start easily but will die 5 minutes later. It dies idling, driving, or even full out. At full out it can bog out and come back. The car will start again a few minutes later. Searching suggests there may be rust from the tank temporarily blocking fuel or the coil is dying. My truck had a similar problem and turned out the power supply to the computer was loose. Can someone tell me where to start testing based on these conditions? Thanks.

[IdahoKidd]

Hello. I see this is your first post so welcome aboard! You say you have used the search, that is a great start. How long has this been a problem? From first time out after restoration or did it work for a while? Have you changed the fuel filter? Did you clean out the tank during the restoration? These cars build a lot of gunk in the tank. Do you have a fuel pressure gauge so that you can see if you loose pressure during the fail? Does it fail faster during WOT? Obviously I am thinking fuel supply, plugged line, trash in the tank, even bad fuel pressure regulator. Member Fastwoman will likely find this thread and can offer advice on searching for connections. Lots of corrosion issues with the Z's in the wiring.

Give a little more of the symptoms, how they come on, how they go away (you say it recovers, does it stay recovered or fail again in 5 minutes?), some history of what you may have already done (how long was it apart, what all did you take apart, etc) When you do find the solution, be sure to post it so the next guy searching can find a possible solution to his problem.

[n2deep]

Hi, thanks for the welcome. I'll try to address your questions without too much rhetoric.

How long has this been a problem?

It just started last spring the last time i drove it.

From first time out after restoration or did it work for a while?

The car has worked great for many years.

Have you changed the fuel filter? No.

Did you clean out the tank during the restoration? No. This car was and is amazingly clean. Imported from CA.

These cars build a lot of gunk in the tank. Do you have a fuel pressure gauge so that you can see if you loose pressure during the fail? No added fuel pressure gauge.

Does it fail faster during WOT?

I have to say not really. I can start it up. Let it idle in the driveway and it will die 5 min. later. It won't restart immediately but will 5 min. later. At WOT the engine stops for a second or two and comes back in.

Yeah I'm thinking fuel supply as well. But I thought the same thing with my truck believing it was the fuel pump, then the distributor, after $600+ it turned out to be a loose power block. So I'm a little gun shy.

One interesting sympton that pushes me toward fuel supply is that rpm's went up and down while idling. Does that help?

[EverRude]

If it was your coil it would probably get hot stop working then cool off and start working again. Did you check and see if it got hot. However coil shouldn't react differently to WOT than idle so that sorts rules it out anyways.

Guess you could add a clear fuel filter to the fuel line temporarily to see if rust is in the system. Or drain tank straining with a clean white towel. I'd shake car a bunch before opening the drain plug to get rust floating around.

The thing that gets me is the 5 min regularity. That says electrical. But the WOT bogging changes that. Well this is an injected car so my troubleshooting ability is nil to none. That ECU and all the supporting sensors screw everything up for me. Gimme carbs.

[Zed Head]

Hi Guys,

I rebuilt/restored my 77 in 2002. The car will start easily but will die 5 minutes later. It dies idling, driving, or even full out. At full out it can bog out and come back. The car will start again a few minutes later. Searching suggests there may be rust from the tank temporarily blocking fuel or the coil is dying. My truck had a similar problem and turned out the power supply to the computer was loose. Can someone tell me where to start testing based on these conditions? Thanks.

You might measure your fuel pressure while the engine is running. If it drops steadily before the engine dies you have a fuel supply problem. If it stays up, around 30 psi, but dies anyway, you probably have an electrical, ignition, or fuel enrichment problem.

[n2deep]

Thanks. The coil was not hot when I retightened its connections. I'm checking the screen inside the fuel pump now and I'll get back to you.

[jazfe]

I had a similar problem with a different car, it would go fine in town traffic but would only last about 5 minutes on the highway. The problem was the points gap in the distributor.

Doesn't sound like a fuel problem to me unless the fuel pump is overheating and shutting off. I would have a look at all the grounds and check all the electrical connections if you haven't already done so.

Edited March 18, 2011 by jazfe
spelling

[n2deep]

OK there is no debris at the inlet screen. So I assume I should install a fuel pressue gauge and confiirm its not fuel?

Regarding electrical/ground testing... I have a volt meter and test light but I'm not sure where/how to begin. Key on start position? Test while it's running? after it dies? and what circuits should I test?

[FastWoman]

I suspect it's electrical. I bet when you run the engine for 5 min, either the coil or the ignition module overheats and/or fails. The WOT thing might be related more to engine RPMs than throttle. For instance, if you were to climb a long hill slowly at WOT and a high gear (lugging the engine a bit), would it happen then? How about if you're sitting in the driveway and running the engine pretty fast at much less throttle. Would it happen then? I'm betting it's more RPM related than throttle related. Just a hunch.

Oh, welcome!

[n2deep]

I suspect it's electrical. I bet when you run the engine for 5 min, either the coil or the ignition module overheats and/or fails. The WOT thing might be related more to engine RPMs than throttle. For instance, if you were to climb a long hill slowly at WOT and a high gear (lugging the engine a bit), would it happen then? How about if you're sitting in the driveway and running the engine pretty fast at much less throttle. Would it happen then? I'm betting it's more RPM related than throttle related. Just a hunch.

Oh, welcome!

Hi FastWoman, IdahoKidd said you would probably chime in. I suspect it's electrical too from my truck experience above. Here are the conditions when it fails.

1. A drive to work, about a 12 minute trip with a few mild hills. It died halfway there about 5 min. from the house without any heavy WOT action. No start. Wait a few minutes and it starts.

2. Start it up and back it into the driveway. Let it set there and idle and it dies in 5-10 minutes. No start. Wait a few minutes and it starts. Repeat and it dies 5 min. later. Repeat and take a test drive and it dies and comes back while moving at WOT 2 blocks from the house.

3. Last Spring when it started I drove it to a meeting about an hour away. Very fast very fun. 2 days later after the meeting, about five minutes on the road toward the freeway I was at WOT going up a slight hill (overpass) and it died and came back a second or two later. I thought I blew the engine.

Does that help the diagnosis? There is one other thing I noticed lately. The thermostat is getting a little sticky. It will go up to 220 before it opens.

[FastWoman]

Well, I think you need a more controlled test. Try this:

Start your car, cold. Let it idle until it dies, and note how long that took.

Then start your car, cold, at the same temperature (maybe the next day). Hold your foot on the accelerator and keep it it a very high idle, perhaps 2500 RPM. Does it die faster now? If it dies faster, it's nothing to do with the WOT. Rather, I bet it would have to do with the firing rate of the ignition system. The ignition is under higher load with higher engine RPMs. In that case I would suspect an ignition overheating problem. I'd first replace the coil. If that doesn't work, then replace the ignition module.

But to be clear, when you say WOT, I'm thinking high revs.

Edited March 19, 2011 by FastWoman

[Zed Head]

A fuel pressure check would be cheap assurance that your fuel pressure is good and constant, before you start replacing parts. I have heard that you can borrow them from the local auto parts stores for free. You said it dies at idle so you should be able to watch the gauge as it dies.

It's always good to know what you have before you start guessing at what you don't have. You can spend a lot of money replacing perfectly good parts, not to mention the time.

An overheating fuel pump or fuel pump relay fits the symptoms, for example. Doesn't care what the engine is doing, just keeps pumping fuel, so would fit the 5 minute factor.