D-Jet problems, temp sensitivity issue Options

[mgphoto]

Hello and thank you for looking.

I have had a very stable car for the last 29 years, stock 1.7 with original D-Jet, except for the addition of a Per-Lux Ignitor (installed 20 years ago, that was the name back then).

The car is maintained and serviced by me and over the years I've replace leaky injectors, vacuum hoses and the AAR, nothing really major has gone wrong with the fuel system.

Little more than a week ago, Los Angeles got a burst of winter, temps in the mid 40's overnight and my very stable car began to have problems with warm up and running.

Starting does not seem a problem, as when cold (at ambient temperature) the engine will start and run for about 30 seconds, long enough for the AAR to begin to close and the idle to drop.

When this begins to happen, the engine begins to stall, the idle drops to 0 but bounces back up, this will happen several times until the engine stalls.


If I am lucky I can restart the engine and it will idle, (at this point if I am not so lucky I will have to restart the engine upwards of 15 to 20 times after which it will begin to idle).


At this point I can not touch the accelerator pedal, pressing the pedal will increase the RPM's but only momentarily as the engine will stall.

After the car has idled for about 10 minutes, it becomes somewhat drivable, sometimes with severe bucking, sometimes stalling.


Within 15 to 20 minutes the oil temp is starting to register on the gauge, and the car runs as it always has, very strong with any hesitation, totally repeatable every time.


I read a number of articles here on 914World about F I problems and the CHT seemed to be the culprit.

Simple enough, swap it out and see what happens.

Well I won't try the glue the washer to the sensor again, as soon as it came in contact with the head the glue broke and the washer fell into the fins on the head.

Just lucky to have another new sensor with another washer on hand.

Not to lose the last new washer I had, I decided to peen the inside of the washer with a small screwdriver and a hammer, in four opposing places, enough to cause the washer to crimp so it would catch the treads and screw onto the sensor so it could not fall off.

Replaced the CHT and found no change!

I decided to look at the temp aspect.

I have been monitoring the engine block temp, head temp and ambient temps with a laser pointer temp probe.

At this point, I believe the head temp of between 70 and 85 deg F is the point were the stalling occurs.

At head temps above 100 deg F the car will idle, at temps above 140 deg F the car will run.

Low ambient temps causes the AAR to stay open longer, the heads heat faster.

Higher ambient temps may cause the engine to stall faster.

Once the oil is warmed up to operating temp the engine runs all day without problems starting and restarting after several hours (engine temps still over 100 deg F)

I believe the problem is fuel related, if it were ignition there would be backfiring when the ignition kicked back in, fuel would still be delivered and pushed though the engine to ignite in the exhaust system.


Has anyone experienced this kind of temperature sensitivity and is there a cure?

Thanks in advance your help in the matter,
Mike

[r_towle]

For kicks, test your cht when cold and hot to verify it works.
The ambient air sensor may be out of spec.

Sounds like either the CHT or the MPS is dying.
I know you replaced the CHT, but maybe it was not the right part number??? check the resistance and match it to what your ECU needs to see...each CHT is different and must send a specific range to the ECU during warm up.

There is an idle circuit in the ECU that is driven by the position of the TPS and those do get worn out or dirty after 40 years...
TPS position, valve adjustment and timing are critical in cold weather.
You may have valves that are a bit to tight...that will cause erratic idle until they are warm..
To loose is better than too tight, especially the intakes...they cause really poor idle when cold.

FI Trigger points may also be a factor just purely based upon age.
mine were.

Here is my setup in the Northeast...and it gets darn cold here.
I drive year round...never an issue with warm up.
No AAR
No Cold Start Injector (wiring or fuel)
No Decel Valve

I have replaced everything else.
New trigger points (weird symptoms...last thing I changed, fixed all my issues)
new ignition every 6 months for me...points, cap, rotor, wires, plug
New CHT
New TPS
New injectors (as they failed)
New injector seals (twice now...long story)
New intake gaskets
All new vacuum lines.

I would suggest that you re-check your valve adjustment when cold.
Recheck your timing and dwell
Recheck your CHT for proper operation.

Rich