1984 32 cuts out under power 108k miles

[198491132]

Good day. Been trying to solve this for sometime now. At various Rpms, engine cuts out completely until gas pedal is left up, then Rpms return. Upon acceleration, starting at 2k. Can be full gas or partial, hot or cold engine. Intermittent but happens 90% of the time.

Replaced :

O2 sensor 90k
both flywheel sensors at 90k
Checked cap, rotor, wires and plugs 107k
Replaced full throttle switch 107k
Checked and repaired vacuum leak (smoke test)107k
Replaced air flow meter 107k
Replaced gas pump and filter 105k

All work done at the 107k mark, car ran great for a single 50 mile run, then next drive after two weeks sitting, failed again.

Appreciate any thoughts, Dave

[mnez]

Check for loose pins in the 4 pin connector on the firewall. These control the fuel injectors and can feel like a random rev limiter if there is an intermittent bad connection, as it did on my car.

[johnman001]

Check and clean the bundle of grounds that bolt to the intake manifold. They terminate in (3) ring terminals. Sometimes the wires entering the ring terminals can break causing intermittent grounding.

Good luck!

[198491132]

mnez, yes...feels just like a rev limiter .......passanger side or drivers side firewall.? Not sure I follow which connection you are thinking of. Will also pull and clean the brown ground wires ..........

[Joe Bob]

When was the last fuel filter change?

[198491132]

Hi joe, fuel filter was changed with fuel pump....only 1000 miles ago.

[DRACO A5OG]

Originally Posted by 198491132

mnez, yes...feels just like a rev limiter .......passanger side or drivers side firewall.? Not sure I follow which connection you are thinking of. Will also pull and clean the brown ground wires ..........

Driver side, can't miss it. Be very careful when lifting the cap the contacts may have corroded. Get a cotton swap and clean the sockets well. +1 check all grounds

[scarceller]

Possible bad DME, do you have another 3.2L car in the area that you could possibly put your DME into? I've seen this exact behavior from cracked solder joints in the DME. I fix a lot of DMEs these days, more and more are failing.

Other possibility is a faulty carbon track in the Air Flow Meter, you need to measure the out put voltage at the AFM output pin. Put the key in ignition then turn to 'RUN' but don't start the engine. Then remove the air filter so you can push the AFM door with a pencil, (eraser side) while measuring voltage across the ground and output pins as seen here:


The output voltage should read below 1vdc with door closed and as you push the door voltages goes up to about 4.7vdc with door fully open. You are looking for a clean sweep with no dead spots in voltage. If as you open the door you get to a spot that vdc drops or goes erratic you have a bad Air Meter.

[Tronicsworld]

CHT Sensor

[scarceller]

When it cuts out does the tach drop to 0 RPMs?
And is it a dead cut out like loss of spark or does it sputter like loss of fuel?
Also, did you have air fuel mixture checked? You need a WBO2 meter for this, but a cutout issue usually is not mixture related.

I already mentioned having your DME tested in another car, if you can do that test the DME and the DME Relay in the other test car. This will rule out those major components.

[198491132]

Hi All, much appreciated feedback. Today I cleaned the four pin connector going through the fire wall. Did get a slight amount of black on qtip, but no corrosion. Also pulled the 12 grounds off the motor by cyl. 1, cleaned them to a bright polish.

Tested the car for 7 miles, all good. BUT, this has happened in the past. Will drive more later today. DME changed out 12k to 15k ago. Hoping it still is good.

Air flow meter changed out 75 miles ago with a used, guaranteed for a year. Ran great for 75 miles, then issue returned, causing me to post this for help.

Let me get some more miles on tonight.......will report back.
When problem occurs , Cut out drops RPM to zero, not like a mixture issue.

Dave

[scarceller]

So engine is turning but the tach drops to 0RPM, is this correct?

Just because the engine cuts out does not mean it stopped turning, if it's still in gear it's turning. This is important because if you are 100% certain the tach drops to 0RPMs then it means the DME lost power or the seed sensor pulses dropped.

Pay very close attention to what the tach does. If indeed it drops like a rock we have a hint on what to look at. You could have a faulty ignition switch, with engine running at idle reach under the dash and tap on the ign switch with handle of a screw driver. You could also have a alarm module that's acting up, the alarm is directly involved in activating the DME relay and if it acts up it COULD cause the relay to power down. You can place a 12vdc test light at DME relay pin #87b (FuelPump feed) and leave the test light in the cabin so you can visibly see it, if the engine cuts out and the light goes out you have lost DME power at the relay.

[scarceller]

Does it cut out and then catch on it's own? or does it totally die and you need to restart it? If it cuts out for a few seconds and then catches again it could be idle speed related. Have you properly set idle speed following factory procedure that has you jumper B&C pins at the connecter on the rear fuse panel? If you have not properly verified idle speed and adjusted it properly per factory procedure you need to do that. I won't go into great details but if the Idle Control Valve pulses get way to short because someone tried to up (force) the idle speed higher than 800RPM for the 84 DME then the DME could be rebooting it self.

First idle speed is baked into the DME program and the early 84-85 cars had idle speed at 800RPMs then 86-89 cars changed it to 880RPMs. You CAN not simply try and force the idle higher, people do this often thinking they just turn the idle bypass screw way out and the idle goes up. The idle does go up but you totally mucked up the IdleControlValve logic in the DME. What does the car idle at?

[198491132]

Hi Sal, more data.....

Tach drops to zero., engine remains turning, whenI I let off the gas pedal, rpm will return.

Idle speed is 800. I have not verified with b/c jumper procedure. Just looking at the tach.

Tapped ignition switch, no change. Ignition switch was replaced awhile back, at 65k miles.

I do have an alarm circuit ...simple on/off pull switch, rarely used.

Will be driving it in the next hour. Great points........

Standbye , thanks !

[mnez]

Originally Posted by 198491132

Hi All, much appreciated feedback. Today I cleaned the four pin connector going through the fire wall. Did get a slight amount of black on qtip, but no corrosion. Also pulled the 12 grounds off the motor by cyl. 1, cleaned them to a bright polish.

Tested the car for 7 miles, all good. BUT, this has happened in the past. Will drive more later today. DME changed out 12k to 15k ago. Hoping it still is good.

Air flow meter changed out 75 miles ago with a used, guaranteed for a year. Ran great for 75 miles, then issue returned, causing me to post this for help.

Let me get some more miles on tonight.......will report back.
When problem occurs , Cut out drops RPM to zero, not like a mixture issue.

Dave

With a thin blade you can spread the pins slightly to be sure the contacts are tight.
We went through all kinds of things before servicing this connector, which finally solved the problem. But my tach didn't drop to zero, so it sounds like you have a different problem.

[198491132]

Update: have taken 2 - 10 mile drives since cleaning grounds and cleaning four pin connector by firewall. Also found possible sensor connection slightly loose ( top of the three) connectors above cyl #3. No issue, still not convinced This was a fix, time will tell.

Thanks! Dave

[DRACO A5OG]

Was it the either two black ones or the white one?

[scarceller]

Originally Posted by DRACO A5OG

Was it the either two black ones or the white one?

The top connector would be the white CHT connector and if that connector was loose it certainly would screw with mixture but would not result in tach drop to 0rpm.

[scarceller]

Grounds are critical, you already cleaned the main ground point at intake runner #1.
Have you inspected and cleaned the braided ground strap that connects the drivetrain to the body? It's located at the front of the trany, near the body mount.
Also inspect and clean the main battery gnd strap at the battery as well.

Those 3 items need to be tight and clean.

[198491132]

Thanks Sal, I just checked the battery ground, looks tight and surprisingly clean. I can not get a good eye on the tranny strap without lifting the car, will do so this weekend. Bentley manual shows many ground points, my as well check them all. Can I use CRC electric spray to help prevent any corrosion, etc?