Hunting idle at stops only Backfire in intake manifold on warmup DWELL reading is odd

[zimvsdib]

I took my car for a test drive yesterday for 45 minutes to my brothers house.

This car worked fine before, but has been a bit of a donor vehicle to get my time car running perfect. So it was sitting for a few months.

I put a newly rebuilt fuel distributor on here from DMCH a few days ago since i harvest this cars functioning distributor for my time car. The car stars up and i adjusted the fuel mixture to level out the idle. It achieved a smooth idle.
Then i put my dwell meter on there to tune it in.

As you can see in the video(posted in the next comment) the needle jump to 10 degrees and doesn't move at all. My other car is set perfectly as you can see from the next video. Also when i adjust the mixture the reading doesn't change. I'm connecting the multimeter clips to the wire connector not the maintenance plug.
Why do i have this reading?

So the idle sounds/responds good. But i don't have any idea where the dwell is at.


TEST DRIVE TO MY BOTHERS HOUSE
Trip there 3pm:
i start the car up to warm it up. from the bay i give it some throttle and hear a pop in the upper part of the engine. Not from the exhaust. Like a backfire in the intake manifold.
I rev the engine a bit more and it seems fine. Doesn't happen again.
The car runs and drives good except every stop light i get a hunting idle or a good 30 seconds, then it returns to normalization. This is all happening at the stop light. Here is a video of the event:


https://www.youtube.com/watch?v=X4lauB4YkTc&list=UUt3Q9J4zT0xKOOhdNODslmg

I installed headliner at my brothers place then i left about 7pm.
Trip back:
I start the car and it does the same thing. by pressing the gas i hear a "pop" and the car also feels like its not going to run well. I wait a minute. I give it some more gas and it levels off and seems fine. Running good.
The fwy is good but when i get to those stop lights i get the same hunting idle for a short time. I can even see my headlights dim as the RPMs go into the dive. But after 30 seconds it goes back to a smooth idle.

I hate that this car didn't have any issues before i replaced that distributor so i always want to point fingers that part. What could be my problem be here?

The Dwell reading and the hunting at stops…

[zimvsdib]

https://www.youtube.com/watch?v=g2wOio1kQT0&list=UUt3Q9J4zT0xKOOhdNODslmg

[zimvsdib]

https://www.youtube.com/watch?v=NKVBgLfqvYs&feature=youtu.be

[Bitsyncmaster]

My guess is your adjustment on the mixture is off. Normally takes less than a 1/4 turn for the dwell to read that 10 degrees to 80 degrees. You just need to keep turning the mixture till that dwell moves off that 10 degrees.

Maybe your O2 sensor died but my guess is just the adjustment.

[djdogbone]

It sure sounds fuel related or fuel mixture related. Maybe the new distributor is no bueno

[David T]

It sure sounds fuel related or fuel mixture related. Maybe the new distributor is no bueno

To be able to adjust the Lambda EVERYTHING on the motor needs to be working well. If the motor needs a tune-up, has vacuum leaks, bad injectors, anything, you cannot properly set the duty cycle. Just because you switched the fuel distributor is not enough to say everything else is OK.

[zimvsdib]

My guess is your adjustment on the mixture is off. Normally takes less than a 1/4 turn for the dwell to read that 10 degrees to 80 degrees. You just need to keep turning the mixture till that dwell moves off that 10 degrees.

Maybe your O2 sensor died but my guess is just the adjustment.

Well when I turn it far counterclockwise the car wants to die. And the needle won't move at all.
Is that reading correspond with an o2 sensor fail?

Is it possible that the ecu is sending a bogus signal?

[zimvsdib]

To be able to adjust the Lambda EVERYTHING on the motor needs to be working well. If the motor needs a tune-up, has vacuum leaks, bad injectors, anything, you cannot properly set the duty cycle. Just because you switched the fuel distributor is not enough to say everything else is OK.

The motor is working great.
I did a complete tune up last year. Zero vacuum leaks on this car.
Newly cleaned injectors. New dist cap and rotor, vac lines, gaskets,orings, spark plugs and wires, water pump, temp sensor. o2 sensor is a year old.

I guess I could just switch the fuel distributors again and see if I get any of these issues.
The one on the time car works perfectly.

[Bitsyncmaster]

If the dwell did not change and you turned the mixture both ways until the engine died then I would guess it is the O2 sensor that died. Just remember the O2 reads the average of all six cylinders so if one is really bad that could cause bit problems.

[Ron]

I wouldn't swap the FD back yet... Do the tests at D:04:15 in the workshop manual -- It will point you in the right direction.

[zimvsdib]

I wouldn't swap the FD back yet... Do the tests at D:04:15 in the workshop manual -- It will point you in the right direction.


If the dwell did not change and you turned the mixture both ways until the engine died then I would guess it is the O2 sensor that died. Just remember the O2 reads the average of all six cylinders so if one is really bad that could cause bit problems.


This is D:04:15
30948

Are these number for dwell readings or something?

Repair guide says the the ECU sets a default higher fuel ratio when o2 sensor is not functioning.

The car does smell rich. I just don't understand how come the needle on my dwell won't budge when i adjust.

I guess ill get a new 02 sensor put in and see what happens next. I'll also get a reading on the control pressure.


Can i get an 02 sensor from auto zone or other auto parts store?
Last time i got one it was from a delorean retailer. I'd like to just go to the store rather than order it. Any one know the part number, i get blank stares if i don't have a PN?

[Bitsyncmaster]

I did read some more of the repair guide and it says like the the ECU sets a default higher fuel ratio when o2 sensor is not functioning.

When the O2 sensor is cold it does not output any voltage. When disconnected no voltage. Not sure when they fail if the voltage goes to high or to low but I think the ECU just uses the zero volts to set that default setting.

[zimvsdib]

thanks Dave! I'm going to get another sensor in the car asap. I'll report back when i get a new one.

[zimvsdib]

I went to auto zone and got a band new o2 sensor even though mine was only a year old and still shiny.

I has the same results. The dwell needle is at 10 and not moving. I kill the car by leaning out the mixture and the needle still stays at 10 till the very end.

Here is the video of what happened. Also you can hear the pop/ backfire in the intake manifold at the beginning of the video when i rev it a little.


https://www.youtube.com/watch?v=9mO_9eV-hVo&feature=youtu.be

[Bitsyncmaster]

It may be your Lambda ECU has gone bad. It seems the ECU failures are rare which is why I guessed the O2 sensor was at fault. If you had a bad connection in the O2 sensor circuit you would get the default higher dwell reading.

[zimvsdib]

It may be your Lambda ECU has gone bad. It seems the ECU failures are rare which is why I guessed the O2 sensor was at fault. If you had a bad connection in the O2 sensor circuit you would get the default higher dwell reading.

Judging by this video would you assume that swapping this fuel distributor with another one would yield the same dwell reading?

Is there any way to test my ECU?

If the ECU was operational and the freq valve or ISM were faulty what kind of reading might someone get?

I appreciate the help!

[Bitsyncmaster]

Judging by this video would you assume that swapping this fuel distributor with another one would yield the same dwell reading?

Is there any way to test my ECU?

If the ECU was operational and the freq valve or ISM were faulty what kind of reading might someone get?

I appreciate the help!

Since your engine will die when you make adjustments, I would think the FD is working somewhat. You may want to do the injector testing with six jars. You can try swapping the Lambda ECU which is pretty easy if you have a spare. You can pull the connector off and temporarily connect the spare.

[David T]

Since your engine will die when you make adjustments, I would think the FD is working somewhat. You may want to do the injector testing with six jars. You can try swapping the Lambda ECU which is pretty easy if you have a spare. You can pull the connector off and temporarily connect the spare.

There is a test procedure in the Workshop Manual consisting of grounding the O2 sensor and seeing what happens and using a 1 1/2 volt battery in place of the O2 sensor. Bad connections can make the ECU appear to be bad so even if the ECU does not pass these tests you still must verify the wiring. The O2 sensor works on VERY small voltages so any bad connection will cause things to not function.

[zimvsdib]

You can try swapping the Lambda ECU which is pretty easy if you have a spare. You can pull the connector off and temporarily connect the spare.
Okay, I'll swap the ECU next. And preform the other 02 sensor tests.

Now i know there are 2. I want need the LAMBDA ECU, thats positioned standing up toward the front of the car.
This one?
30967



Not this..
30966

[Bitsyncmaster]

Okay, I'll swap the ECU next. And preform the other 02 sensor tests.

Now i know there are 2. I want need the LAMBDA ECU, thats positioned standing up toward the front of the car.
This one?
30967



Not this..
30966

Yes the Lambda ECU is the one standing up. Connector has one clip on one end. Pull that clip out and then the connector will lift from that end. Other end has a "U" that clears after the other end is lifted high.

[Grover]

I had an issue a couple of years ago where the dwell would not read/set correctly at all. It turned out to be one of the connectors in the valley. The wire corroded off the connector. It was the lambda switch (#25 http://store.delorean.com/c-270-1-3-0-water-pump.aspx). Once that connection was fixed I was able to tune the dwell. Might be worth checking out if you can.

[zimvsdib]

I had an issue a couple of years ago where the dwell would not read/set correctly at all. It turned out to be one of the connectors in the valley. The wire corroded off the connector. It was the lambda switch (#25 http://store.delorean.com/c-270-1-3-0-water-pump.aspx). Once that connection was fixed I was able to tune the dwell. Might be worth checking out if you can.

interesting… thanks for the tip.

[zimvsdib]

I just swapped the LAMBDA ECU unit.

The Dwell meter gave me the exact same reading.


I still haven't tried the AA battery/ ground on the 02 sensor.
How many wire connections are in the LAMBDA system? \ the ECU, the #25 LAMBDA sensor, the o2 sensor….
and any plugs in-between.

[Horsebox]

I would do the 1.5V battery test on your current ECU if I were you. That will prove if your lambda ECU is good or not.

After doing that test and assuming the ECU is good, I'd get both your system pressure and control pressure checked.

Good luck, the battery test is much easier than it reads...

[zimvsdib]

I completed both o2 sensor tests recommended to me. My DWELL meter had zero change with either test, so I started looking at other threads with this kind of symptom. There was one thread with a comment from DMCMW Dave mentioning a ground wire that connects to the back of the intake manifold. He said it could give funny readings when unplugged.


- make sure you didn't knock off the ground wire that comes off the back of the passenger intake runner, and goes about two inches to an inline connector (what were they thinking?). That's the ground reference for the ECU/O2 sensor and if disconnected it acts really strange. . .

It was unplugged on my car. After reattaching the wire. I had a real DWELL reading.
That ground wire was the problem. My FV started to buzz and i could adjust/set my dwell to 40 after that. I took it for a test drive and had no "hunting idle" issues at stops. That was solved as well.


My only issue now is my cold startups. I still have those backfires in the intake manifold and the engine sounds fuel starved when revving it. After it warms up for 2 minutes its fine. This may be the fuel distributor or possibly the fuel pump?
Also: The FV on this car is much louder than my other one. The constant buzz is almost annoyingly loud(normal?).


Here is a video showing the meter as i unplug the ground and adjusting the mixture screw to achieve a proper dwell. You can hear that loud FV turn on and off when i unplug the ground.

https://www.youtube.com/watch?v=gl1rDxKzfNA&feature=youtu.be

[zimvsdib]

here is my new idle. It still has some tiny rpm fluctuation that annoys me. My other car is pretty perfect so I'm not sure why this is.
Not terrible, but hey I'm going for perfect.

Dave (Bitsyncmaster) would your new redesigned ECU fix this issue or is this a good place?



https://www.youtube.com/watch?v=PUnWcHf2LUk&feature=youtu.be

[Rich]

My only issue now is my cold startups. I still have those backfires in the intake manifold and the engine sounds fuel starved when revving it.

After it warms up for 2 minutes its fine. This may be the fuel distributor or possibly the fuel pump?

Good description of symptoms. The problem is neither the pump nor the fuel distr.

Check the vacuum hoses/connections back from the warmup regulator (WUR, aka control pressure regulator or CPR). Until the coolant temp reaches 40deg C at the thermal vacuum switch the WUR is designed create an enrichment spike upon cold acceleration.

The WUR needs to see the correct vacuum signals at both of its ports - and be working - for the system to perform correctly. There are other components in play as well as the WUR itself but start by making sure the two WUR vac hoses are solid. The WUR is mounted on top of the left valve cover at the rear, behind the oil filler neck.

You are right to be shooting for 'perfect' and you might be pretty close to that.

[Bitsyncmaster]

Dave (Bitsyncmaster) would your new redesigned ECU fix this issue or is this a good place?

That little hunt is not to bad. Mine is a little less than that. I would not know if my ECU would reduce that or not but I would suggest you keep finding the engine problems (your cold run) and you may get that hunt reduced with those fixes.

[zimvsdib]

The WUR needs to see the correct vacuum signals at both of its ports - and be working - for the system to perform correctly. There are other components in play as well as the WUR itself but start by making sure the two WUR vac hoses are solid.

Thanks for the help Rich! I will check on this now. I put in new Vac hoses last year but i'll double check it all. I could also pull the a working WUR from my other car if needed.

I picked up a vacuum gauge with the intention of installing it in the system. I'm not sure the best point to make the in-line insertion tho. any thoughts?



That little hunt is not to bad. Mine is a little less than that. I would not know if my ECU would reduce that or not but I would suggest you keep finding the engine problems (your cold run) and you may get that hunt reduced with those fixes.

Well i may want one anyway :) Thanks Dave!

[zimvsdib]

WUR hoses are perfect and hooked up correctly.

What should i try next?

[Rich]

WUR hoses are perfect and hooked up correctly.

What should i try next?

Try verifying that you are getting a vacuum signal to the rear fitting of the WUR after cold start, engine idling.

Pull the hose off of that fitting and put a vac gauge on it before you start it. Report.

[zimvsdib]

Thanks Rich, i'll try that tomorrow and see what i get.

[alexwolf1216]

Thanks Rich, i'll try that tomorrow and see what i get.

Did you ever figure out the issue?