Engine Cuts Out

[Jetaway]

Hi,

I have a 240Z modified with a 280ZX dizzy. In retrospect, the problem may have been showing over the last 2 months, but it has only become acute within the last 10 days.

The problem isn't reproducible, but is predictable. The engine will cut out, completely, not just a power fade, for between 1/2 second (maybe less) to at least 20 seconds. When cutting out for 1/2 second, the engine fires back up if I'm moving because of a compression start. Feels like a stutter, which may have thrown me off on the diagnosis. These short cut-outs usually occur in clusters of 3 to 4 times and have possibly been occurring sporadically for a couple of months. Within the last week and a half, in addition to episodes of stutter-cuts, I've been unable to restart the engine for up to 20 seconds using the starter. (I stop trying after 20 seconds, no sense beating a dead horse.) A minute later, it fires right up and I'm on my way. I've driven, probably for anywhere from five to ninety minutes after a cut-out and it may or may not occur again.

The problem appears to be heat-related, specifically under-hood temperature and not just operating temperature related. I say this because: 1) summer is finally arriving here in the Great Central Valley with highs pushing 90 (still, unusually mild for July) and 2) the problem has, so far, only occurred after the classic heat stress scenario of 30+ miles of highway driving followed by stop and go urban driving. It is definitely increasing in frequency, however.

My Z also has an electric fuel pump installed with wiring of somewhat dubious expertise. When the problem started, I suspected it may be the cause, but I've checked and rewired where necessary and also replaced the fuel filter, if only for good luck. I've also ruled out a fuel supply problem because the cut-out is so abrupt and total.

The distributor cap and rotor were worn after 30k miles, so I replaced them. I've checked and tightened connections to the battery, distributor, and coil. Still getting the cut-outs, in fact they are becoming increasingly common.

Other than the total loss of power (other than!, that's funny) the car runs fine. Power may be off a trifle, but that could be anything from my imagination to a change to summer gasoline to normal aging through a tune-up cycle.

I'm close to 100% positive that the problem is electrical and strongly leaning towards either the coil or electronic ignition module. It would seem awfully odd to me for the coil to fail with these symptoms. But since in 30+ years of owning used cars, I've never had a coil fail on me, I really wouldn't know how a bad coil would manifest itself. Nonetheless, the symptoms seem more typical of a transistorized unit. The module is marked E12-80, which I've seen as the part number in a couple of posts. Before biting the bullet and running down what appears to be a difficult to find and somewhat pricey part, I'd thought I'd ask those who know far more about cars and Z's than me if I've overlooked something. Something, hopefully, cheaper and easier to locate than an E12-80.

Chris Hebert

[stevef1972z]

Somebody help this guy, I dont have the update on my 240 so I cant really help.

[bigoak]

Ummm...taking a flier here...but given that the problem occurs with heat, any chance you might be looking at vapor lock?

[Nigel1943]

Jetaway, have you ever had the gas tank cleaned out? Could be some crud floating about in the tank and occasionly blocking the outlet.

Edited July 12, 2009 by Nigel1943

[peterc]

My first guess would be something electrical as well Chris. If I understand correctly this seems to be an either/or situation. Runs normal or not at all. Power on, power off. Does it ever cut out on you when stopped or at idle, or only when you're moving? If only when moving, could be bad connection that's affected by vibration. Next time it happens, pull over and see if there are any extra hot wires. If its a bad electrical connection you'll know by the heat. When it cuts out, can you still hear the fuel pump running, assuming you have an electrical pump?

Any other electricals affected when it cuts out? Radio, guages, lights, etc still work? Have you tried (CAREFULLY) wiggling any accessible wiring under the hood while the car is idling to see if you can reproduce the symptions?

Edited July 12, 2009 by peterc

[Jetaway]

My first guess would be something electrical as well Chris. If I understand correctly this seems to be an either/or situation. Runs normal or not at all. Power on, power off. Does it ever cut out on you when stopped or at idle, or only when you're moving? If only when moving, could be bad connection that's affected by vibration. Next time it happens, pull over and see if there are any extra hot wires. If its a bad electrical connection you'll know by the heat. When it cuts out, can you still hear the fuel pump running, assuming you have an electrical pump?

Has cut out both when moving and sitting still. Haven't felt up the wires, but will do so. Fuel pump is annoyingly loud and yes, it keeps running.

Any other electricals affected when it cuts out? Radio, guages, lights, etc still work? Have you tried (CAREFULLY) wiggling any accessible wiring under the hood while the car is idling to see if you can reproduce the symptions?

Everything else seems to work, though now that I think about it, it hasn't happened at night, so it's possible lights cut out. Done a bit of wiggling, haven't been able to kill the engine.

I saw a reference on classic z cars to using a GM HEI (LX-301) ignitor that costs $16.00. Eventually came across the following instructions:

http://www.dimequarterly.tierranet.com/articles/tech_hei.html

I figured what the heck, if it works, great, if not, $16.00 is pretty cheap for a diagnostic flyer. I patched it in so that I could quickly revert to E12-80 without much in the way of tools. Happy to say that it does work. Unfortunately we are experiencing an unusually cool stretch of weather and am unwilling to make a declaration whether or not the problem has been solved. It is supposed to hit triple figures and stay there by mid-week, so I should be able to make a call on whether the problem has been solved by Friday.

Chris Hebert

P.S. The referenced article mentions making a plate to cover up the space in the distributor normally occupied by the E12-80. If the GM ignitor is a keeper, I think its possible to kill two birds with one stone by mounting it on a heat sink in such a manner as to also cover up the open space on the distributor. Sure would make for a neater installation.

[Jetaway]

Jetaway, have you ever had the gas tank cleaned out? Could be some crud floating about in the tank and occasionly blocking the outlet.

No, but pulling the gas tank to figure out why it is so difficult to fuel up and eliminate an overpowering gasoline smell when filled and especially after spirited driving has been on my to-do list for a couple of months. Just haven't been able to coordinate help, a reasonably empty tank, and not having a more pressing problem to solve to get it done.

Have made some headway on the gas tank problem. The vapor? line that makes a 180 degree turn was pinched off during an installation at some time. Figure that can't be good.

Chris

[Nigel1943]

Could be the pump is "annoyingly loud" because it's sucking air.

[260zCaliCar]

When my fuel pump became "extra loud", I started getting vapor lock with similar symptoms to yours. Replaced the fuel pump, never happened again.

FWIW

Mike

[Jetaway]

When my fuel pump became "extra loud", I started getting vapor lock with similar symptoms to yours. Replaced the fuel pump, never happened again.

FWIW

Mike

Interesting, I assume an electric pump.

Drove around a bit yesterday with the temps in the mid-90s. No cut-outs.

Today, it will be even warmer,, currently 83 degrees en route to a predicted high of 103. Getting ready to take a long drive to the nearest Fry's electronics (child looking for a PS3 game unavailable in town). If the trip is uneventful, I'll be willing to call the problem solved by replaced the ignition module. If not, I'll investigate the fuel supply, including the pump, again.

Chris

[bigoak]

Yeah, I still think you're looking at something fuel related. I can't think of pieces of the electrical system that are that sensitive to ambient air temperature...and Z's of a certain period were notorious for vapor lock...

Hey, you should move to Canada...no vapor lock and free health care to boot (note the Canadian accent when I said boot...)

[Jetaway]

I wrote:

Hi,

I have a 240Z modified with a 280ZX dizzy. In retrospect, the problem may have been showing over the last 2 months, but it has only become acute within the last 10 days.

The problem isn't reproducible, but is predictable. The engine will cut out, completely, not just a power fade, for between 1/2 second (maybe less) to at least 20 seconds. When cutting out for 1/2 second, the engine fires back up if I'm moving because of a compression start. Feels like a stutter, which may have thrown me off on the diagnosis. These short cut-outs usually occur in clusters of 3 to 4 times and have possibly been occurring sporadically for a couple of months. Within the last week and a half, in addition to episodes of stutter-cuts, I've been unable to restart the engine for up to 20 seconds using the starter. (I stop trying after 20 seconds, no sense beating a dead horse.) A minute later, it fires right up and I'm on my way. I've driven, probably for anywhere from five to ninety minutes after a cut-out and it may or may not occur again.

The problem appears to be heat-related, specifically under-hood temperature and not just operating temperature related. I say this because: 1) summer is finally arriving here in the Great Central Valley with highs pushing 90 (still, unusually mild for July) and 2) the problem has, so far, only occurred after the classic heat stress scenario of 30+ miles of highway driving followed by stop and go urban driving. It is definitely increasing in frequency, however.

Chris Hebert

I am going to have to call this one solved. Since replacing the E12-80 ignition module with a GM LX-101 ($15.00) a couple of days ago I've put 350 -- 400 miles on "Smiling Jack," with outdoor temperatures poking into the low triple digits, and I haven't experienced one instance of the engine cutting out.

I used "Using a HEI Ignition Module with a Factory Electronic Distributor" by Brendan Parrot as a basic guide:

http://www.dimequarterly.tierranet.com/articles/tech_hei.html

One difference was I mounted the GM HEI directly on the distributor in the place of the old E12-80. I mounted the GM HEI on an aluminum plate 3 7/8ths by 2 3/8ths. Dimensions aren't real critical, though you'll run into clearance problems with a much bigger plate. I always have a bit ... bit of fun, that's it, a bit of fun getting drilled holes to line up exactly, but I think for mounting the plate to the distributor, 2 3/8ths will do. Though you may want to take your own measure. You'll want to replace the existing screws with M4X10 (or M4X8) pitch = .7 because the E12-80 is considerably thicker than the aluminum plate and it won't snug up if you use the original bolts. Mount the LX-101 on the aluminum plate using whatever works, though you'll need to keep the bolts short for clearance. Make some new electrical connectors however you feel fit and you're pretty much done.

I'll probably splurge and buy the heavy-duty LX 101 ignition module ($35.00) and keep the original one around as a spare.

Chris Hebert