'76 D-Jet Hard Start After Hot, Used to Flood

[Brian Mifsud]

Still working out bugs in my '76 2.0

Car was flooding (like 1/4" fuel in intake manifold) before I disconnected the cold start valve. I have yet to test the valve to see if it is faulty by removing it and sticking it in a jar (per Dave Darlings recommendations). Questions:

Are there any conditions inwhich a GOOD cold start valve would still flood intake manifold (i.e. it is "told" to stay open??)

My ECU has no numbers identifying it on the exterior that I can find (although someone went nuts with a rattle can of black paint all over the engine at some time in its history) Are the numbers identifying the ECU stamped into the housing? Are they inside on the mother board? I'm pretty sure its the WRONG ECU becuase the mounting brackets don't match up with the firewall mounts.

Also, once hot, the engine doesn't want to maintain idle and becomes exceedingly hard to restart after it eventually quits (like after 10 minutes of driving). Am I barking down the wrong tree checking my head temp gauge?

thanks

Brian

[bd1308]

There is a THERMO TIME sensor under the plenum with a heating element installed. Its a dual circuit, meaning that when you start the car two things Happens.

But lets look at the reason why this sensor is needed.

In cold weather when the engine is started, the ECU sends a signal to the thermotime switch to heat up the internal element.

That's the THERMO part of the switch.

Now the time switch comes into play the instant the engine is starting. The switch is being heated at a certain degree, and depending on how COLD it is when first started, there is a mathematical function that relates the OUTSIDE temperature to the amount of TIME the sensor stays on. Basically, the colder it is outside, the longer it takes for the sensor to heat itself to some precalibrated value, and therefore the longer it stays on.

In essense, with this circuit somehow broken and the 2nd part always connected, the sensor stays on, therefore flooding out the plenum in short order. Usually there is either some corrosion at one of the crimped terminals or there could br a break in the wires going to the thermotime switch.

What I would do first is to take the connector off of the CSV and verify that thsi in fact the cause, next I would test the connections at the connector for the thermotime switch (located UNDER the plenum--2 pin connector) and look for 12V on one side, that should be the heater, and then by grounding out the OTHER side, you should be able to control the CSV.

Inside of the thermotime switch is an internal heater, which was mentioned before, and then there also is a set of bimetallic flaps that open the circuit when the temperature inside the sensor reaches the precalibrated value.

Lemme know if you need more help

b

[Brian Mifsud]

b

I'll check out the Thermo Time Switch to establish whether the cold start valve is getting the wrong signal.

thanks

Still curious about the head temp sensor for those of you who are knowledgeable.

[bd1308]

what do you need to know about the head temp sensor?

I know about that too

b

[Brian Mifsud]

Also, once hot, the engine doesn't want to maintain idle and becomes exceedingly hard to restart after it eventually quits (like after 10 minutes of driving). Am I barking down the wrong tree checking my head temp gauge?

[bd1308]

I would check HOT idle (remember 1500 RPM idle when cold is normal) then check at your timing and dwell (48-55 degree dwell, 27 BTDC timing at 3500 RPM)

Then look at your head temp sensor, along with just the general condition of your harness. Corrsion = raised resistance, which as you may or may not know actually is the main method of operation of D-Jet.

On my car, the trigger point connections were loose, I had one HUGE lag at the 1000-1700RPM level, and when hot there were extra pulses, which made it hard to run.

Three crimp connectors and problem solved, for some time.

b

[Dave at Pelican Parts]

Note that the TTS only provides the ground for the CSV. The power is actually taken from the yellow wire going to the starter, so the CSV is only powered when the starter is actually cranking!

--DD

[bd1308]

then why have the time function in the sensor at all?

[hardflex]

a bad MPS would make it run very rich. Fuel System always thinks it's at full throttle......

[ptravnic]

You could chase your tail for years posting symptoms & getting numerous "answers" here on the board. There's one sure fire way to chase the gremlins away...

Make sure all the mechanicals are sound - do not pass go, do not collect $200, go directly to valves, points, condensor, timing. ONLY THEN start reading through the bible of D-Jet:

http://members.rennlist.com/pbanders/

godspeed bother.

-pt

[Dave at Pelican Parts]

Originally posted by bd1308
then why have the time function in the sensor at all?

I don't know. For people who have to crank the starter for a long time? Or for start-shut down-restart cycles that are very quick, e.g. backing the car out of the garage or some such?

The "time" function was not added until the 75-76 model year, BTW. Earlier cars just have a thermoswitch, with no heating element.

--DD

[Bleyseng]

Originally posted by Brian Mifsud
Still working out bugs in my '76 2.0

Car was flooding (like 1/4" fuel in intake manifold) before I disconnected the cold start valve. I have yet to test the valve to see if it is faulty by removing it and sticking it in a jar (per Dave Darlings recommendations). Questions:

#1.Are there any conditions inwhich a GOOD cold start valve would still flood intake manifold (i.e. it is "told" to stay open??)

#2. My ECU has no numbers identifying it on the exterior that I can find (although someone went nuts with a rattle can of black paint all over the engine at some time in its history) Are the numbers identifying the ECU stamped into the housing? Are they inside on the mother board? I'm pretty sure its the WRONG ECU becuase the mounting brackets don't match up with the firewall mounts.

#3. Also, once hot, the engine doesn't want to maintain idle and becomes exceedingly hard to restart after it eventually quits (like after 10 minutes of driving). Am I barking down the wrong tree checking my head temp gauge?

thanks

Brian

#1. No, unless like BD1308 stated the TTS is bad.
#2. The ECU doesn't mount to the firewall it mounts to the edge of the batterytray with a special mount so you can pull it out. (see pic) UNLESS you have AC which means the Dealer mounted it to the firewall anywhich way they could. There are stamped numbers inside the ECU.
#3. The idle needs to be adjusted "HOT" as the engine needs to be fully warmed up or else the AAR valve is still open or the CHT is still richening up the AFR. A slumping idle when hot usually means its too rich! So after the engine is hot, adjust the idle mix via the ECU knob and the airbypass on the TB using a CO meter or by ear.

[Brian Mifsud]

Bleyseng,

Thanks for marching through each of my questions so directly. Nice engine bay!


I used to have all the correct parts in my 76 so I recognize the bracket you have in the photo.. .the one I have now is most certainly NOT the stock ECU.

I'll post back with my findings tomorrow evening.

thanks

[hardflex]

#1.Are there any conditions inwhich a GOOD cold start valve would still flood intake manifold (i.e. it is "told" to stay open??)


if it was "told to stay open" simply unplugging it would have fixed the problem. if it didn't, then it's stuck open.

[pbanders]

Originally posted by bd1308
then why have the time function in the sensor at all?

Someone else may have answered this already...

The "time" part of the function was to prevent flooding when cranking for a long time. This may be related to the "hot start flooding" problem that's the topic of the thread.

The "hot start flooding" problem seems to be fairly common with D-Jet 914's. As best as I can tell, the problem is due to either a leaky CSV, or more likely, leaky injectors. What I think happens is that after the engine is run to operating temperature, then shut off briefly (e.g. go into the store for 10 minutes), the fuel loop remains pressurized. This is intentional, to enable rapid restarting. However, if you have one or more leaky injectors, the fuel in the loop dribbles out into the cylinders, and you have a very rich condition on start.

Note that the problem may also be due to an ECU design flaw, though I've never figured out how it happens.

The "fix" for the problem is to check everything out, find the flooding source and replace it. If that doesn't help, and the problem happens again, there's another thing to try. Before turning the key, depress the pedal to the floor, and hold it there. Now, turn the key, keep the pedal on the floor, and crank until it starts. By depressing the pedal before turning the key, you avoid injecting additional fuel into the intake ports (from the action of the throttle switch), and by holding pedal down you increase the amount of air available for the flooded engine to start with. Old trick you learn with a flooded carb (and sticking a screwdriver handle into the automatic choke to hold it open, too).

[pbanders]

One more thing to check - make sure the TTS is seeing 12V ONLY when cranking. It may be miswired - a fairly common problem on 30-year-old cars.

[Dave at Pelican Parts]

If the wire to the TTS breaks off or falls off, and touches the crankcase, you can dump a whole lot of fuel into the manifold while trying to start. (Band-aided that one at the autoX with some electrical tape...)

--DD