D-Jet issues, Hot start idle problem, and stumble @ 3k rpm Options

[DRPHIL914]

I have been fighting an issue for a while but it seemed to be intermittant.
- when car had been running and is good and warm but gets shut off. If i restart lets say in 5 minutes or so, say for gas or something, upon starting it the idle wants to drop out and die if i dont keep idle up with pedal- this lasts for about a minute or so, then it seems it will level off and idle normally.
- i had read about issues with the CHT - the one i have was new a about a year ago, - tested as correct at that time-
- this issue appears to be worse recently- did happen to a lesser degree when on the octeenerfest trip.
- i have also noticed that watching the AF meter, that over the past month or so it seems my start up and warm running ratio has been slowly changing- getting more lean, could that be from the CHT? would the CHT resistance slowly change over time?
MPS tests out o.k, and that usually defaults to rich right?
- so i had read about adding some resistance inline to the CHT( i did this a few years ago, so i have a couple rheostats in my bag- yesterday after driving hme i stopped at lowe's, came back out and startedthe car, idle was so upand down, wanting to kill, it was hard to keep running. - so i stopped it and put the variable resistor in line to the CHT, set @ 250 ohms,, the restarted the car and rather than die out or have to keep the idle up with accelerator pedal, it started smooth and ran just fine, - BTW if i tried to change the idle richness iwth the ECU idle knob it didnt matter -

Testing over the past 2 days i have seen this: the CHT when warm, upon stopping and restarting the car, seems to have the wrong value, getting warmer maybe while sitting- sending a bad signal to the ECU - adding the additional resistance has gotten rid of the bad restart idle when warm, AND now rather than running lean at hwy speeds- 2800rpm,@ 60-65(was getting up around 14-16, and in past had been @12.8-13.5 at most, now is running more around 12.5, and cold idle, start up about 10-11.

Conclusion: bad CHT ? or something else - it was beginning to happen sometimes even when warm and sitting in traffic, idle wouuld be fine and then all of a sudden being to drop and vary, even try to die. .

Now the stumble- Probably the TPS - but that board is new just a year ago, and less than 2500 miles using it. I will try to do a cleaning on it and see if that matters but should not be worn already! Got the board from dave sprinkle. r

with the additional resistance in line my warm ide is right around 950-1000rpm and a bit more rich than it was before but this seems much better. - car seems to now be running a bit cooler at highway speeds

i think i need to get and test ad different CHT and a new TPS board!!

any suggestions from other D-jet users would be great -

[BeatNavy]

Hi Phil -

So the situation I THINK you're describing about the car wanting to die after restarting when warmed up is, I believe, a normal one. I think it's called something like "warm start over-enrichment" or something (it's on the Anders site). Basically what's happening is that the heads cool faster than the block when you stop the car. Because of that, the CHT is over-enriching the fuel/air mixture resulting in a low idle (mixture too rich). Once the head/block reaches operating temp again it should level off. Adding any mod that further enriches the mixture would make the situation worse, I would think, so I'm surprised what you did actually seemed to help, unless maybe the CHT is going bad (or the wiring to it).

rc

[DRPHIL914]

Hi Phil -

So the situation I THINK you're describing about the car wanting to die after restarting when warmed up is, I believe, a normal one. I think it's called something like "warm start over-enrichment" or something (it's on the Anders site). Basically what's happening is that the heads cool faster than the block when you stop the car. Because of that, the CHT is over-enriching the fuel/air mixture resulting in a low idle (mixture too rich). Once the head/block reaches operating temp again it should level off. Adding any mod that further enriches the mixture would make the situation worse, I would think, so I'm surprised what you did actually seemed to help, unless maybe the CHT is going bad (or the wiring to it).

rc

Thats what i was thinking, but based on input from the A/F meter it seemed more lean, not rich, and again, it was also ahppening when sitting in traffic sometimes as well.
Mywiring the F.I. harness was an new one from Jeff B. last year. so i think that is good, I have had issues with the grounds working loose but that results in a rough running and is easily checkd and taken care of. So i think i will pull the CHt this weekend and test it to see where the values are now vs when installed . This seems like the most likely problem. THe mps is not leaking, but i have another that will be rebuilt soon and i might give it a test to see if it changes the outcome as well. .
Phil

[BeatNavy]

So you are getting conflicting signals. Wow. (IMG:style_emoticons/default/screwy.gif)

Didn't see if you said in the post, but has the CHT ever been replaced?

Good luck. The nice thing about 40+ year old D-Jet: keeps you on your toes! (IMG:style_emoticons/default/smile.gif)

[DRPHIL914]

So you are getting conflicting signals. Wow. (IMG:style_emoticons/default/screwy.gif)

Didn't see if you said in the post, but has the CHT ever been replaced?

Good luck. The nice thing about 40+ year old D-Jet: keeps you on your toes! (IMG:style_emoticons/default/smile.gif)

yes, i replaced it when i did the FI harness , injectors, vac lines, new throttle body and intake runner seals etc all about the same time. other than the ECU, i think i have replaced most everything.

- really its not horrible, kind of anoying. and the stumble issue is maybe more aggrivating than anything. I have heard of the air temp sensor being an issue too, but that was replace new as well.

- this weekend i am putting in the new oil pressure relief valve from Tangernie, i had been rnnng a bit hot on the highway but i really think since it seems i was running more and more lean that thismighthave been part of it as well.

[BeatNavy]

So you are getting conflicting signals. Wow. (IMG:style_emoticons/default/screwy.gif)

Didn't see if you said in the post, but has the CHT ever been replaced?

Good luck. The nice thing about 40+ year old D-Jet: keeps you on your toes! (IMG:style_emoticons/default/smile.gif)

- really its not horrible, kind of anoying. and the stumble issue is maybe more aggrivating than anything. I have heard of the air temp sensor being an issue too, but that was replace new as well.

I get funny results sometimes that I think are related to the air temp sensor, but it generally has a "weak" influence on mixture (at least relative to CHT or MPS). When running cold I sometimes get wild fluctuations in idle, and others who experienced that who had a Air Fuel meter said that it normally happened when their mixture suddenly went lean tracing it back to faulty air temperature sensor. In my case I think the sensor is ok (the readings test out okay with an ohmmeter) but I think I have a short in the leads that surfaces periodically. But you have a new wiring harness, so....stumped.

[Chris Pincetich]

(IMG:style_emoticons/default/popcorn[1].gif)
I'm dealing with a slight 2600-3000 RPM intermittent "stumble" as well. Sucks when it's time to move, and the car "hiccups."

I disconnected the TPS and it "mostly" went away. You could try that...
Since my early TPS board is not available easily to easily replace, I bent the little contact arms and that really helped for about a week, but the stumble is starting to manifest again.

I am eager to learn what you find and others advise (IMG:style_emoticons/default/beerchug.gif)

[dknechtly]

What kind of ignition do you have? Points? Pertronix?

[DRPHIL914]

What kind of ignition do you have? Points? Pertronix?

Hot - spark , which cam recommended from a long time porsche mechanic here. I don't think that's the issue but I could replace it with another. Also thought about the advance plate and ground strap in the distributor. So I will vet those tomorrow. I have a nice like new 2nd distributor with new everything in it. I could swap it out as another test but then I'll have to go back and reset timing dwell etc.
I will keep you posted on the results. I have a new one of everything but a cht and mps (I have one it has vac but someone messed with its setting) so I have a line on a tps replacement and will order a cht from automotion .

Thing is that stumble is not exactly at the same time always and it's not every time. Sometimes I accelerate strong right thru that point no issue..
It could be my mps has decided to cap out. I have 2 rebuild kits and will tackle this on one of the spares I picked up a while back.

[914_teener]

My thoughts side with the TPS for what it is worth.

I would check your distributor like you are going to do and see what happens.

Setting dwell and timing is not that big a deal.

Doesn't sound like a MPS problem at all.

[DRPHIL914]

My thoughts side with the TPS for what it is worth.

I would check your distributor like you are going to do and see what happens.

Setting dwell and timing is not that big a deal.

Doesn't sound like a MPS problem at all.

- getting a TPS to test with, - but over the weekend even at idle it gets this sudden stumble like its going to die, - not an up and down idle hunt like with a vac leak or in a really lean running condition. does not seem like the TPS could cause that- it does not happen when cold or warming up, only after hot. - thought id get at it yeterday and check the distributor closer-but never got time due to lawn work ) driving to work today running about 60-65, never hesitated or stumbled when driving at a constant speed.

[r_towle]

Just get a nice simple set of webers, they are much better.

[DRPHIL914]

Just get a nice simple set of webers, they are much better.

(IMG:style_emoticons/default/lol-2.gif) (IMG:style_emoticons/default/chair.gif)
ive been down that road before (IMG:style_emoticons/default/slap.gif)
my trip to octeenerfest and back my avereage MPG was almost 34,
ive never heard of carbs doing that (IMG:style_emoticons/default/poke.gif)
seriously, rich, unless its the TPS, i dont think its injection related, - it could be the distributor ground strap , coil, points, and those would still be factors with carbs.
I'll get it figured out.

(IMG:style_emoticons/default/evilgrin.gif)

[r_towle]

It was a joke

[DRPHIL914]

It was a joke

I know (IMG:style_emoticons/default/drunk.gif)