Engine dying at random intervals (1987 Targa)
 

Hey all,

My car has been running flawlessly for the past year except for the alternator crapping out one Sunday along with a bad spark plug wire which our sponsor gladly exchanged for me. Now I've got a weird issue. Please bear with the long explanation, but I want to put all the "data" out there.

1987 Targa, no special mods. I do have a modern radio with Amplifier. Amp is powered by direct hook up to battery. I also have the dual Keuhl condenser setup with the electric fans powered by the fuse panel in the engine compartment. I've confirmed that they are wired correctly.

To start: All running great! AC is running perfect. Vent temps in the high 30's here in Houston. Not bad eh? Ok driving on highway in rain and engine cuts out for millisecond. Almost like a misfire. Drive another 5 minutes and it does it again. After playing around, I realize its happening when the AC compressor and condenser fans cycle on.
Car never has that issue again, but I also don't have rain event either. I search for bad connection and can't find it. I figure I have a funky ground somewhere.

Next: It starts happening more regularly in last month. or so. Finally, the car dies on Thursday nigh with no AC running. Idling rough, feels like bad spark plug wire. I get home, back onto ramps and shoot each exhaust port with temp gun. All running hot except Cyl 6. Remove spark plug and it is completely fouled with hard crust. I scrape off, clean plug well and restart car. Runs fine! Now that temps have cooled off, I remove fuse from dual Keuhl condensors. Just trying to figure out what's going on. I took photo of spark plug, but it didn't come out well enough to tell anything from it.

This morning: Sitting in driveway letting car warm up. idling at 1000, heater, defroster, windshield wipers on. Car just dies. Almost like someone turned the key off. I restart and it runs fine all the way to work.

I did notice that I can hear a relay cycling on and off when sitting in the car. I do notice the headlights give a slight flicker when the relay cycles. Is this a DME relay issue? I had actually replaced the old one with a new as preventative maintenance. Alternator was rebuilt, but only one back of diodes were replaced. Issue? I figured I would have had this issue 12 months ago when it was rebuilt.

Ok, what the hell is going on? I really want to get some ideas to troubleshoot while I'm off next week. Once I get this gremlin figured out, I'm ordering suspension parts.

Thanks in advance for any help!

Jason

Sounds like potentially a couple of issues.

Recommend you check all your engine grounds first. There are three of them I can recall off the top of my head. First is on top of driver side intake manifold at front. Second is on driver side engine compartment wall next to fuel filter. Third is under car on passenger side in front of starter next to transmission. Any of these being sketchy could cause the car to run rough or randomly die.

With regard to the issues in the rain, you are most likely getting some sort of shorting going on w/ spark. How old are your plug wires? I'd look at these carefully and replace if they are aging. Would not be a bad idea to check coil and cap/rotor while you are at it.

Is the relay cycling issue tied to when the AC compressor kicks on? Does it happen w/ all of your accessories turned off and the car is just idling? If it happens w/ accessories on, you need to just go thru them one at a time until you find the culprit. I can't ever recall hearing the DME relay making any noise ever. Even when it fails.

One other thing to test is with a volt meter at the battery when you have your accessories turned on. If you are having charging problems you would see a drop in voltage at the battery.

These issues are not fun to troubleshoot. I hope others chime in.

Check the alternator again. Sounds like when the compressor/fans kick on, the voltage drops enough to cause the cut out. When the alternator is jacked with, that seems to be the problem area. Make sure your voltage/amperage source is good and go from there.

Plug wires are less than 12 months old. They are Clewett Racing. I did notice that when fooling with plug wires I could get the car to stall if I grounded out the plug. My guess was that the coil was draining off entirely and couldn't keep it running.

Relay cycling is with AC off. Its the only way I could hear it. Its is ever so slight. Headlights were on when I noticed it. No other accessories.

Duh... I haven't checked voltage. I'll do that as soon as I get home today. I'm going to pull #6 plug again. I wonder if the plug is bad....

I'll do that! I may pull it and take it to the rebuilder down the street and get him to check it again. It has a warranty on the rebuild.

Lately, I've found several bad ignition coils. They do put out a spark of sorts, but apparently not enough. Car gets towed in, I do all the normal checks and they all check out ok. Has everything but won't run. Hmmm, I wonder if it's another coil issue. Replace it and the car fires right up. Things do seem to come in clusters.

Wow, that is disheartening. Buddy's 86 is going thru the same thing. Placed his DME into my car and it started right up. His coil ohms out fine but unfortunately can not check under load. Swap is the only real test.

These coils ohmed out fine also.

I have a sparker box for testing coils, two electrodes facing each other but on threads so one can adjust the spark gap. IIRC a good coil should spark at about an inch maybe less. John maybe you have one of these old timer testers around.

Can you ID the relay that's clicking? Put your hand on the DME relay is that the one clicking? You did not say if you hear the relay clicking with key in RUN engine stopped or key in RUN engine running, can you articulate this better please?

I agree with John on bad coils I've also seen a few lately but what I also am seeing a lot is cracked solder joints in DMEs, I fix at least 1 every month or 2. And about 1/2 of the DMEs that come in have cracked joints that are not yet causing issues but they are cracked and will certainly get worse with time.

As for alternator issue, I advise you look at charging voltage while at idle then rev it to 3000RPMs and look again. Then apply tons of electrical load like head lamps AC, ... and measure again. While running you need to be between 13.2 and 14.8vdc

Thanks guys! You're great!

I'll spend some quality time with my baby this weekend....

Finally got a chance to look at voltage. 12.8 when running. 12.0 with headlights. 10.8 with everything on (headlights, fog, heater, AC)

Think I found my problem!

I'll say !

Another reason to have a voltmeter on the dash.