Really hard electrical problem

[Xenn]

So im here again, i only ever show up when i have a problem I cannot solve, this one i have been racking my brain on for most of a year.

The car: 1978 280z, mostly stock, lots of new parts and a spart car to check parts against.

The problem: Occasionally the car will have an extremely rich running condition, it will barely run, idles around 400, has no power and giving it any throttle usually kills it. Rarely this will happen when i am driving. Usually it is after i run it then stop (such as to run in a store) come out and this manifests. It acts somewhat like as if the ECU is running in a worst case senario, and as the car gets hotter it runs worse until it dies and wont start.

Its not fuel pressure, new sparkplugs and wires, ignition coil, cleaned distributor cap and basically every ground in the whole car, new AFM, injecters, TPS, basically you name it, ive swapped it out, next on the list is ECU just to see if it helps (since i have a spare).

 

Heres the kicker(s) whoever owned it before me A sucked with electrial systems to the point where the heater didnt work because he plugged the harness (the power side of the switch to motor to harness 3 way connecter) upside down, like crammed it in backwards then sold it as a broken blower motor, so who knows what else they screwed up elsewhere (fuse box is a mess too) and then B at some point an aftermarker alarm was installed, then disconnected, but looking at part A, who knows well.

 

So here are my questions, if it is electrical, what could cause it, and if its the alarm, how do i go about looking up what type it is and finding instalation instuctions? (I could only ever find a patent # never a buisness, even with google.)

[Dave WM]

next time out try opening the hood after stopping, then see if restarting gives you the same issues.

You say is seems rich, how do the plugs look.

Have you replaced the temp sensor? have you cleaned the electrical connections esp around the temp sensor including the bullet connectors.

If the plugs show rich check the function of the cold start injector.

Check the FSM for these symptoms.

 

[Zed Head]

12 hours ago, Xenn said:

Usually it is after i run it then stop (such as to run in a store) come out and this manifests. It acts somewhat like as if the ECU is running in a worst case senario, and as the car gets hotter it runs worse until it dies and wont start.

Might be the old "hot start" issue.  We collected some stories and solutions a short while ago.

http://www.classiczcars.com/forums/topic/48810-hot-start-issue-with-efi-who-has-it-who-doesnt/

 

[Xenn]

Its not that, it can manifest as soon as i turn it off, and occasionally while driving, and it only gets better after the car has been turned off.

I say it runs rich because i can see the carbon in the exhaust coming out, until i adjusted the TPS the car actually generally ran lean.

All new injecters, including cold start, and i really did clean every connector i could find in the engine bay (as well as label all the wiring on the ecu harness.

New temp sensor, temp gauge sensor, and thermotime.

Oh and ive ran it with the hood up with it doing it before, and recently, wiggled connections and played with the throttle, made sure coolant was circulating all of that. Nothing helps.

 

Worst is sometimes it will go a month or two without doing it, sometimes twice in a week, usually worse when there is a lot of rain, and i live in Washington. 

[Zed Head]

The guesses can only be as good as the facts.  Actual times would help,  Occasionally, after, after the car has been turned off...kind of vague.

Random problems are difficult to solve.  The ECU is one thing that seems to go bad on a random basis, and running rich is a symptom.  It's an uncommon problem though.  Try thumping the side of the ECU and/or wiggling the cable next time it happens.  Or try another ECU if you can borrow one.  Worse when it's rainy could be a humidity thing, which can affect electronics.  My other car's radio craps out in the rainy weather.  And these ECU's don't have a limp-mode.  They always do exactly the same thing based on inputs, when they're working correctly.

Did you problem happen before you adjusted the TPS?  

[Xenn]

Hmm, i thought i replied over the weekend...

Anyway, usually the worst times are after I stop, it can be as short as turning off the car, getting out, checking mail, and getting back in. It is usually worse the sooner I try and restart the car.

It can also happen while driving, ive been stranded in a few intersections becsuse of it, ususally the RPMs will jump from 700 or so to 900-1000 for a split second then fall to 4-600 and barely run with no power, gassing it kills it, black exhaust (not nearly to the point of coalstacking, but black exhaust, not clear). It starts and stops as fast as someone flipping a switch.

Occasionally ill get a little hickup while driving, a split second lack of power like the engine died for a moment or had really bad fuel/spark issues.

I thought the ECUs had a fail mode that could run the car until it started to get up to temperature where it would die because it was treating it like a cold engine, am I wrong?

And i replaced the TPS the day i posted this thread, it hasnt had a no start condition yet since, but has still had the "hickups".

[SteveJ]

No "Limp Mode" in the early FI. With these ECUs it usually runs or it doesn't from everything I've read.

[Zed Head]

31 minutes ago, Xenn said:

ive been stranded in a few intersections becsuse of it, ususally the RPMs will jump from 700 or so to 900-1000 for a split second then fall to 4-600 and barely run with no power, gassing it kills it, black exhaust (not nearly to the point of coalstacking, but black exhaust, not clear). It starts and stops as fast as someone flipping a switch.

The tach behavior is a sign that the igniton module might be going bad.  You might try the GM HEI swap.  It's cheap and you can actually do a temporary install by the coil to check it out.  If you want to do a clean permanent install, check this thread out.

 

[Zed Head]

Forgot to say, one sign is that the tach needle doesn't follow engine speed exactly.  So if you see that needle jump but don't hear the engine speed up...not good.

[Xenn]

Ive been waiting to do the distributor upgrade until the atlantic z car club tech tips website was back up, and by damn its finally back. Ill swap out the distributor/ignition module this weekend.

 

[siteunseen]

3 hours ago, Xenn said:

Ive been waiting to do the distributor upgrade until the atlantic z car club tech tips website was back up, and by damn its finally back. Ill swap out the distributor/ignition module this weekend.

 

Thank you!  Good news for us that like to do our own work on a budget.  Way to go @Blue 

[stanfurfiord]

A problem I discovered a few years back and thought it was the airflow meter, turned out to be voltage regulator, it would get warm and voltage would drop below what air flow meter needed to function. Went to Bosch regulator and also replaced alternator because they work together. Problem solved, now have spare airflow meter.