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

[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.

[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?

[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?