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Old 02-18-2013, 13:53   #1 (permalink)
mac
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'98 Crown Vic, 4.6L SOHC - dies intermittently

Hey guys,

We have a '98 Crown Vic, 4.6L SOHC with approx 115k miles. Yesterday, sweetie left the house and it died within about 3/4 mile. It started right up again, so she drove back home.

I checked some connections, reseated fuses in the primary box near the battery, cleaned battery cables, tested battery and charging system, and all seemed well.

She left this afternoon and it died again, at about the same place. But this time it had idled for about 10 minutes before she left. And was about 15-20 minutes before it would start again (the starter spun it over just fine, and she tried it every few minutes).

I checked for ignition switch slack, but everything seems fine. So I had her drive it in a loop from the house driveway thru the shop driveway and on the road back to the house driveway. In 15-20 minutes, it died twice, but started right up again each time.

My OBD reader detects no codes whatsoever. All electricals work and the engine runs perfectly smooth with no hesitation.

It was running low speed (< 20mph) each time it died. Any ideas?
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Old 02-18-2013, 18:31   #2 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

When it stalls and won't start, check the fuel pressure. When it wouldn't start, did you hear the fuel pump run a few seconds every time the key was turned to run?
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Old 02-18-2013, 20:48   #3 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

That's the problem... it only failed to start once when the wife was away from the house, and she has no idea what went on during her attempts to start it. There's no sputtering or missing when it dies, it just acts like the key was turned off.

It's always held fuel pressure well, the pump only clicks after it's set a few minutes. If you shut it off and turn the key back on soon after, it's still pressurized and doesn't click.

I'd think the lack of error codes should narrow things down a bit, but I don't have enough experience with ECU systems to really know. And as long as it it fires back up immediately (with no OBD codes), I've no idea what to test.

Thanks.
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Old 02-19-2013, 05:26   #4 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

Sounds like your PCM power relay may be giving you issues.

http://repairguide.autozone.com/znet...52801e4c24.gif

How to Check a Car Electrical Relay and Wiring Circuit Test - 2CarPros
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Old 02-19-2013, 10:03   #5 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

Hmmm... since that relay controls most everything, wouldn't an error code show up somewhere? Or would it just think the key actually was turned off?

A semi-related question...

I've heard that if the engine dies, you should always turn the key off before trying a restart so everything in the ECU can reset properly. True? Or does it matter?

Thanks.
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Old 02-19-2013, 14:12   #6 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

An error code usually will not show up.
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Old 02-19-2013, 14:39   #7 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

Quote:
Originally Posted by mac View Post
Hmmm... since that relay controls most everything, wouldn't an error code show up somewhere? Or would it just think the key actually was turned off?

A semi-related question...

I've heard that if the engine dies, you should always turn the key off before trying a restart so everything in the ECU can reset properly. True? Or does it matter?

Thanks.
First part: If the relay opens, the PCM will look at it as the switch was turned off.


For the second part, it depends on what caused it to turn off, some diagnostics will auto reset when the condition clears. If your relay truly is the problem, it's looking at it like you turned it off which means reset not required.
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Old 02-19-2013, 15:20   #8 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

OK, so that's a place to start. Supposed to be stormy here for a couple of days, but I'll try to post back when I learn something.

Many thanks to both of you.
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Old 02-24-2013, 15:43   #9 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

And...

It seems you were right about the power relay, though it wasn't the relay itself. Finally got around to checking things this afternoon.

I had sweetie start it up, then tapped the relay assembly and various connectors with a screwdriver handle. Nothing happened.

So I unclipped the relay assembly cover, and as I slid the assembly out of the cover, the engine died. I told her to leave the key on.

The red wire going to the power relay was horribly loose. I could touch it and the relay would click on and off. I pulled the relay and popped its cover off to make sure, but everything looked pristine inside (coil connections, contacts, etc.). So I buffed the contacts with a piece of card stock for good measure and put it back together.

I then removed the other relays and diode (which tested ok), and popped off the yellow piece that allows access to the wire connectors. Removed the red wire (and yellow, since it also looked a bit wide), crimped the female spade connectors for a snug fit on the relay, and put everything back together.

It idled ok for about 1/2 hr, and ran just fine on a test drive.

I really appreciate the help guys. Best wishes.
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Old 02-24-2013, 17:35   #10 (permalink)
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Re: '98 Crown Vic, 4.6L SOHC - dies intermittently

Good to hear!
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