D-jet masters question/help needed, very low idle/stall when motor is hot Options

[DRPHIL914]

I think this has been getting slowly worse but I dont really run the car for a long drives around here and its been cold too, but yesterday during a longer drive to a PCA event, on my way back having a lot of stop and go traffic after the motor had warmed up and reached full operational temperatures, my idle was dropping below normal , about 500-600, and after stopping for gas and sitting for about 10 minutes idle was normal (1000rpm)

Motor is 2056 with d-jet, with ignition 123 distributor.
fuel pressure is perfect, timing etc all good. all sensors were put in new when this motor was built 3-4 years ago. and i have always left the idle about 1100-1200 due to the fact that when it was fully hot it would come tdownt o 850-900 but never wanted to stall.

My thought is that the CHT is acting up and the resistance must be too high hot and now is sending a signal making it just like normal d-jet would get heat sink if a hot motor sat for a short time then wouldnt start. - is that a lean or rich condition that happens i cant remember but looking for your ideas thoughts here.

Phil

[914Sixer]

I would check fuel pump first. Heat is a killer for pump.. Are fuel lines wrapped to prevent boiling off(vapor lock)? Where is fuel pump?

[DRPHIL914]

it’s a 75, fuel pump up front, it’s maybe only 2-3yeara old

and fuel pressure was good(i have an inline fuel gauge)

will check this when it gets hot and see , supposed to be doing AX this coming weekend,

[DRPHIL914]

my other thought on the cht would be to pull it and put it in some oil, check resistance when oil temp is around 300 degrees or so to see where its at.

i hate just swapping parts but i do have several other cht's but this one is not that old it was i believe one of the ones made by 914rubber.

Phil . - also could add a pot. in line, a variable resistance that could be dialed in, i ahve 2 of those in the box from 15 years ago when i was dealing with cht issues and the hot start issue on the original motor way back when i first bought the car and was sorting thru the many issues at that time.

[emerygt350]

Another possibility is that it is not running correctly when cold and the compensation for the high cold idle is causing it to run at low rpms when hot.

[emerygt350]

do you have an AFR gauge in it?

[JeffBowlsby]

Here is another thought.

Maybe the 'below normal 500-600' is actually normal - what the air bleed screw is actually calibrated to. When idle later increased to 1000, it was really reacting to a free air leak. If this is true, then you might look for a small air leak allowing free air in, somewhere in the intake system. Suggest using a smoke pencil to explore.

[DRPHIL914]

Another possibility is that it is not running correctly when cold and the compensation for the high cold idle is causing it to run at low rpms when hot.

do you have an AFR gauge in it?

Yes i have an A/F , but the O2 sensor is sometimes throwing a error code sometimes and either may need to be cleaner or replaced i believe its no longer working correctly,
-
I do need to order a new one from Summit or Dakota Digital.

[DRPHIL914]

Here is another thought.

Maybe the 'below normal 500-600' is actually normal - what the air bleed screw is actually calibrated to. When idle later increased to 1000, it was really reacting to a free air leak. If this is true, then you might look for a small air leak allowing free air in, somewhere in the intake system. Suggest using a smoke pencil to explore.

Jeff, i suppose this is a possibility, so i can recheck these areas, motor has been together for a couple years and about 5,000 miles. Tuning as you know, on a 2056 using d-jet can be a challenge but it has been running really well, It was on a dyno a few months back and at that time the AF used by them showed it pretty much where we want it for mixture until about 4800rpm then from there to 5500 it gets lean but at a cruzing rpm and part load it was perfect. hwoever certainly i can make sure i dont have a leak.

but since the beginning with this motor with all new seals etc its always required a bit more air at idle with the idle air screw partly open , it is timed correctly , no vac canister on the 123 distributor is hooked up no not having the vac retard on, but even with out this the idle would be very low. I am also going to recheck timing again but with the 123 the last 3 times i checked, it was spot on.
If i had an air leak wouldnt you suspect that the idlw would be too high not low at temp?

[iankarr]

Forgive me if thesse suggestions sound basic...they're more for anyone less experienced who comes across this thread later (IMG:style_emoticons/default/wink.gif)

Have you tried turning the adjustment screw on the CPU? Do just a notch or two at a time and wait a minute to see the effects.

Does the RPM value of your timing light agree with the RPMs shown in the 123 app? The 123 is more of a "virtual" unit, so if the dizzy isn't "synched" to the real world, there will be an offset in your timing curve. Easiest way to synch (for anyone who hasn't done it)...

– Clear out all points and set one point at 10 degrees @ 1000 rpm and one at 27 degrees @ 3500.

– Set your timing light for 27 degrees

– Rev the engine up to 3,500 as shown on the timing light and turn the dizzy until you see whatever mark you're using line up to the correct spot.

– Lock down the dizzy. It's now synched to reality. Load (or re-load) your timing curve.

[emerygt350]

You may want to try a cheapo Amazon o2. Air cooled engines from 50 years ago are hard on them. I suspect you are rich but that may not be the problem here.

[MDTerp]

My vote is for CHT sensor. I had a similar running issue on my 75. Replaced the CHT sensor and found the old one like this. New one fixed the problem. I carry several with me now.

[mgphoto]

What could be happening is your voltage regulator is cycling, after a bit of discharge the battery needs topping up and there is extra drag from the alternator.

[rfinegan]

A tight valve will show as a slight / miss fire and lower the idle speed when hot and may not be as noticeable at driving speeds.. Set your valve lash if you have not done this recently to be sure.

[DRPHIL914]

Forgive me if thesse suggestions sound basic...they're more for anyone less experienced who comes across this thread later (IMG:style_emoticons/default/wink.gif)

Have you tried turning the adjustment screw on the CPU? Do just a notch or two at a time and wait a minute to see the effects.

Does the RPM value of your timing light agree with the RPMs shown in the 123 app? The 123 is more of a "virtual" unit, so if the dizzy isn't "synched" to the real world, there will be an offset in your timing curve. Easiest way to synch (for anyone who hasn't done it)...

– Clear out all points and set one point at 10 degrees @ 1000 rpm and one at 27 degrees @ 3500.

– Set your timing light for 27 degrees

– Rev the engine up to 3,500 as shown on the timing light and turn the dizzy until you see whatever mark you're using line up to the correct spot.

– Lock down the dizzy. It's now synched to reality. Load (or re-load) your timing curve.

my 123 is a early one so no blue tooth connection.

but its set at 30 degrees advance on 3500rpm just a slight increase from stock 28 and is not changed, i did set valve clearance 2 weeks ago , the #1 both were loose at .008 and were put back to stock and was not an issue that i could see right after doing this

[DRPHIL914]

You may want to try a cheapo Amazon o2. Air cooled engines from 50 years ago are hard on them. I suspect you are rich but that may not be the problem here.

good idea i will take a look,

[DRPHIL914]

My vote is for CHT sensor. I had a similar running issue on my 75. Replaced the CHT sensor and found the old one like this. New one fixed the problem. I carry several with me now.

What could be happening is your voltage regulator is cycling, after a bit of discharge the battery needs topping up and there is extra drag from the alternator.

A tight valve will show as a slight / miss fire and lower the idle speed when hot and may not be as noticeable at driving speeds.. Set your valve lash if you have not done this recently to be sure.

- will double check the CHT sensor for sure, to see if we are having issue with this,

- will check voltage when hot next time it runs to see, i can tell you guys that upon stopping i ttried to loosen the idle screw when it was doing this and hoping that would increase idle but it had zero effect , after cooling off and restart idle was then hight due to this and had to tighten it back down and idle was right at 1000 after that but i didnt run it for long and was not heated up,

- i think im going to take a close look at the voltage and the CHT and then if nothing checks out here i might then double check the valve lash again, but it was checked 2 weeks ago when i did the valve covers seals due to leaking, and again, it has always done this slightly but was consistent that it was 1500 idle cold, 1100 warmed up but lowered to 850-900 hot not like suddenly now where its trying to stall out and drop to like 500-600.

will chase this down this week so hopefully i dont have issues driving it down to and in theAX this weekend.

PHil

[emerygt350]

I kinda suspect it is going pig rich if that idle adjustment made no difference. Could be the cht problem mentioned above. The other sensors just don't add enough fuel to cause a drop like that. Might want to check the other temp sensor just in case.

[DRPHIL914]

new O2 sensor ordered and on the way to be delivered tomorrow, getting this working will help with my tuning.

Yesterday i verified my CHT is a 012, and no wire or connection issues
-. checked for air leaks, removed the air cleaner, it was a bit loose at the throttle body, remounted and tightened down-
- checked alignment static timing then actual timing is right on.
- I might swap out the CHT or add the spacer that Brad M sells, will see.
other than that, i'm going to install the new O2 sensor tomorrow night and prep for AX,

will see how it runs this weekend. I always recheck pre-AX lug nuts, exhaust, suspension , brakes, etc etc. clutch and accel cables, but i always take extra cables, coil, fuel pump relay board, MPS, relays etc with just in case.

my gut feeling is that its the CHT and the resistance when fully hot is off making mixture rich, but the AF should tell me this if its working correctly if/when this happens again. Its supposed to be highs in mid to upper 60's so unless i get stuck in traffic driving home i will not have the car running long enough to reproduce the conditions i saw on sunday.

[DRPHIL914]

I kinda suspect it is going pig rich if that idle adjustment made no difference. Could be the cht problem mentioned above. The other sensors just don't add enough fuel to cause a drop like that. Might want to check the other temp sensor just in case.

agreed- going to bring with my usual kit and i have several extra sensors- we shall see...