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]

one cure that seems to work, and at the end of the day it is a compromise, is to put in a resistor.
If you go to radio shack the resistors are fairly cheap.

to figure out which resistor you may need, in your specific circumstances, with your specific car, I would suggest putting a POT inline with the CHT.

A POT, or an anjustable potentiometer is availabe at radion shack for about 5 bucks.
get one that goes from zero to 1000 ohms, that is the range you will be testing.
Unplug the CHT and using two small wires with the proper male and female spade bits fastened to them, wire the POT inline.
Start at zero to see of the car start (this is just like it was before you put the POT in place...zero resistance)
Start the car and start turning it up .
It takes maybe 10 seconds or more to even out the idle...so go in small steps and be patient.
Once you have the idle correct, you now need to drive it.
Use tape to hold the POT at the setting you just found that works when the motor is still cold.
Then, take a ride around till it warms up.

Here is where the compromise comes into play.
You may end up turning it down a bit when warm because you will end up running richer than before...

It takes two or three times to really get it perfect...that is two or three cold starts with the know turned down a little until you find the sweet spot that is good for cold start, and good for warm running.

Once you find it, unplug the wires from the pot and using an ohm meter, check the resistance across the two poles of the POT and that is the resistor you need to install in place of the POT.

If you wanna get fancy...run wires to the CHT and place the POT in the cabin and you can adjust it anytime you want.

Most people just figure out the resistor and wire that inline and call it a day.

Using the POT, instead of trying ten different resistors, is just one approach to figuring out what it wrong.



Rich