Idle / Lean running - 87 Head Scratcher

[almostordinary]

Hey gang,

Thought I finally found my lean horrible low RPM issue and took the car out and it's still stumbling all of this happened after a very wet wash (especially water in the engine bay):



Laundry List:
- Clean IAC
- Clean AFM (Didnt open the internals this time)
- Smoke Test (No leaks)
- New Plugs
- Replaced #6 wire as it had green corrosion (likely from water sitting as the plug sits upward)
- New Cap
- New Rotor
- New Fuel Pump
- New Fuel Filter
- Additional Ground to block
- New O2 Wideband
- New Alternator Pulley
- New Alternator Belt
- Replaced Focus 9 DME with Stock new Porsche DME
- New Cylinder Head Temp Sensor

When I start the motor everything sounds great, AFRs are around 13.8 - 14.2

Once load is put on the car is begins to buck a bit, then at a stop idle is all over the place and the motor leans out.

When I get on it, up to and before ~4000RPM it runs like crap, then at 4k it pulls like normal.

Wondering if it may be time to look at a new AFM? I did the sweeper clean a while back.
Anyone have a spare 3.2 AFM sitting on a shelf I can try out?

Looking for Cooler heads prevail. picked a hell of a time to do a dry June/July... I need a drink.

Any help appreciated.

Thanks,
Ian

[917_Langheck]

Make sure the idle closed switch is set correctly, and is working. Open the full throttle switch to see if it engages at the correct time. Check how many turns out the idle air bypass screw is turned out - should be between 2 and 4 - this is one air leak that is necessary and controllable.

[almostordinary]

Thank you!

I will check this out this morning.

Another thing I will also look at are my plugs. I was just going through receipts...

I went from WR-7-DC+ to NGK BPR6ES, since they were available at O'reileys in a pinch.

Dropping down that heat range.

I am going to do the above tests and look at the plugs that have been driven ~30miles and compare them to the pics I took of the plugs I took out that were maybe 6 months old... wish I didn't toss them.

I'll head to O'Reileys and pick up the BPR7ES and take it out for a spin and see if that gets to the bottom of my engine's hesitation. Maybe the pre-ignition is all due to the heat range.... although I was having symptoms similar to what I am facing now, but with all the fresh parts, it could be that the plugs are exacerbating the symptoms.

Will report back.

Thanks,
Ian

[almostordinary]

Ok.

Interesting series of events.

I checked the Throttle switch, everything within spec. At 1mm of engagement it loses continuity. Per Bentley.

I checked the resistance in the IACV, all within spec, with the keyed ignition on, I can hear it whiring up. All good.

I decided to pull the plugs to give a visual inspection and they were toast. White on the lead and blued on the top... way too hot.

I swapped in some maybe 700 mile Bosch WR-7-DC+ that I cleaned up.

Took the car for a spin... pulled hard at all RPM ranges... thought I was in the clear.

Got on a bumpy road.. par for the course in LA... hit a couple of bumps and bam... it's searching for idle. Running rich and exhibiting all the symptoms from before.

The plugs definitely brought the car back to life.

Now I have to find out if I have a short somewhere?

Going to do some research, as I think I had a similar problem on my actual build thread... but that turned out to be a bad CHT sensor and a cracked hose on my FPR vaccuum port.

Any other suggestions welcomed... getting close. Want to keep documenting for prosperity and anyone else coming across this issue.

Thanks,
Ian

[wazzz]

You did mention you checked the throttle switch, but that is the idle switch. Fine, did you also check the WOT switch? Should close at around 70% of throttle range. Try to wiggle it while testing continuity on the full range. It should not close on lower range.

[almostordinary]

Just checked the WOT switch. ~75/80% it gets continuity. Checked at the throttle plate and with pedal. Same outcome. Even took a small mallet to it to recreate "bumps" nothing. Continuity only at 75/80% throttle to WOT. Was really hoping to find a smoking gun.

Im going to get under the car later and look at the speed sensor. I replaced one a little over a year ago... it must have been the engine's original, as it was super worn.


Still scratching my noggin on this one.

[almostordinary]

Also did the AFM test, all continuity and voltage sweeps were in the correct ranges. I took the AFM apart over a year ago and changed the sweep angle, so that all seems good to go.

I ordered two new crankshaft sensors, as I just realized I only replaced one on my last go round, so to save myself time I am going to replace both now. When I get to that I will check for any additional loose wiring/etc that may be the culprit.

[scarceller]

You must have a WBO2 gauge? You mentioned that at initial startup AFR is 13.8? That's far to lean for dead cold.

Dead cold initial startup should be in the 12s or lower.

Also, test cold start as follows to be sure ICV and idle switch are doing the job correctly.

- Dead cold engine
- Do NOT touch the gas pedal during any of these next steps!
- Start engine, should idle around 1100RM or more at initial cold start
- Observer initial behavior, if it sputters it's lean if it hunts for idle up and down it's rich
- Over next 3-5 minutes the idle speed MUST slowly come down on it's own till it lands in the 850-900 RPM range 86-89 cars or 800-850 for 84-85 cars.

If initial idle speed was above 1100 and after 3-5 minutes of idling it came down on it's own to spec 850-900 then we know ICV and idle switch are functioning properly.

Initial AFR cold should be in the 12s and fully warm idle in the 13.8 to 14.5 range with O2 sensor unplugged.

If you have a stock O2 sensor still and it's plugged in, unplug it to see if problems clear up. You could have a faulty O2 sensor.

To diagnose further you really need a WBO2 gauge. If you have one, what the AFR at idle fully warm?

And what's the AFR in 3rd gear 3000RPM, stead state cruising on level road? Needs to be in the 14s.

Originally Posted by almostordinary

Hey gang,

Thought I finally found my lean horrible low RPM issue and took the car out and it's still stumbling all of this happened after a very wet wash (especially water in the engine bay):



Laundry List:
- Clean IAC
- Clean AFM (Didnt open the internals this time)
- Smoke Test (No leaks)
- New Plugs
- Replaced #6 wire as it had green corrosion (likely from water sitting as the plug sits upward)
- New Cap
- New Rotor
- New Fuel Pump
- New Fuel Filter
- Additional Ground to block
- New O2 Wideband
- New Alternator Pulley
- New Alternator Belt
- Replaced Focus 9 DME with Stock new Porsche DME
- New Cylinder Head Temp Sensor

When I start the motor everything sounds great, AFRs are around 13.8 - 14.2

Once load is put on the car is begins to buck a bit, then at a stop idle is all over the place and the motor leans out.

When I get on it, up to and before ~4000RPM it runs like crap, then at 4k it pulls like normal.

Wondering if it may be time to look at a new AFM? I did the sweeper clean a while back.
Anyone have a spare 3.2 AFM sitting on a shelf I can try out?

Looking for Cooler heads prevail. picked a hell of a time to do a dry June/July... I need a drink.

Any help appreciated.

Thanks,
Ian

[scarceller]

Save few $$ and order BMW sensors, they are perfect match just few inch longer harness. Our host has these.
Bosch # 0-261-210-002

https://www.pelicanparts.com/More_Info/0261210002.htm?pn=0-261-210-002-INT&bc=c&SVSVSI=0579

Originally Posted by almostordinary

Also did the AFM test, all continuity and voltage sweeps were in the correct ranges. I took the AFM apart over a year ago and changed the sweep angle, so that all seems good to go.

I ordered two new crankshaft sensors, as I just realized I only replaced one on my last go round, so to save myself time I am going to replace both now. When I get to that I will check for any additional loose wiring/etc that may be the culprit.

[scarceller]

Un-bolt the DME from under the seat, then start engine with it un bolted. Now lift the DME few inches and drop it with engine running. The engine should not stumble, if it does you likely have bad DME solder joints. I fix these often and have correct methods and process to repair these.
Common failure is the ignition circuit goes bad with failed solder joints.

Other common failure is the ignition switch, with engine running tap on front side of ignition switch with screw driver handle and also wiggle key.

Finally, test battery voltage! Engine off better than 12vdc
At idle above 13.0 vdc
At free rev 2500 should be high 13s low 14s
A bad battery or charge voltage can cause all sorts of issues in the DME.

[scarceller]

Best spark plugs for the 84-89 3.2 are, but gap them at 0.7 to 0.8mm (no wider)

NGK 6637 BPR6EIX Single Iridium Spark Plug

Post pics of plugs please.

[almostordinary]

Thanks for the input, have a 2hr board meeting call then will get back to all of these.

Already purcha$ed the sensors so that money is gone!

I will do the tests as suggested scarceller.

Didn't even think the DME would be the culprit, but would be a great spot to do a slight drop test.

I bought it newly reconditioned from Steve W along w his tune when I was building the car up. but definitely worth the test to rule everything out.

Thank you

[almostordinary]

.. and yes I do have an AEM wideband. I replaced the Bosch sensor.

[76FJ55]

Originally Posted by almostordinary

.. and yes I do have an AEM wideband. I replaced the Bosch sensor.

If you replaced the stock O2 with the WBO2, are you running open loop or are you feeding the DME a simulated narrowband signal from the AEM?

[almostordinary]

I had to look at my older posts... it looks like I did the following:

"I'm going to do the white wire to the green stock wire setup, since my car has a CAT and I want to have the DME know it's not in open loop."

https://forums.pelicanparts.com/12130536-post113.html

But I need to check... this car's been perfect aside from it now taking a nose dive.

[scarceller]

Be aware that the AEM gauge has a little rotary switch inside that MUST be changed to position 4 if you want the white wire to output a narrow band signal. You must change the switch.

So, for now just leave the stock O2 harness disconnected, this will put the DME in 'Rest Of World' open loop mode. Actually best to do this while diagnosing issue.

If you did not change the switch then the signal going out the white wire is 0-5vdc signal and this will saturate the DME O2 input signal well above 1vdc. If that happens the DME sees a false rich condition and will lean the crap out of your mixture!

[almostordinary]

Yup I changed the switch to position 4, which i will also re-check, on install for the correct reading.

Thanks Sal,

I will be back at the car in an hour or so and take all these suggestions to work.

[almostordinary]

Ok so just hopped back on the car.

Below are pics of the NGKs vs the Bosch that did quite a bit of mileage.

I just put everything back together. Still waiting on the crank sensors.

I readjusted the AFR to be a bit richer at start up and they are hovering around 13.8 to 14.5 in ROW open loop (stock O2 no longer sending a loop back to the computer).

I also tapped on everything while the car was idling and nothing including the DME / Computer had any effect. I went as far as to lift the car and check the trans/body ground and all is good.

I'm going to take it on a brisk run and see how things are getting along.






The NGK Copper Core Plug BPR6ES got extremely hot, as you can see in the actual discoloration of the portion above the threads and the white tip.

Sal, I may check out the plugs you recommend after I do a few more shake downs if this next drive goes to plan.

I'll report back.

[mysocal911]

Originally Posted by scarceller

Un-bolt the DME from under the seat, then start engine with it un bolted. Now lift the DME few inches and drop it with engine running. The engine should not stumble, if it does you likely have bad DME solder joints. I fix these often and have correct methods and process to repair these.
Common failure is the ignition circuit goes bad with failed solder joints.

Other common failure is the ignition switch, with engine running tap on front side of ignition switch with screw driver handle and also wiggle key.

Finally, test battery voltage! Engine off better than 12vdc
At idle above 13.0 vdc
At free rev 2500 should be high 13s low 14s
A bad battery or charge voltage can cause all sorts of issues in the DME.

Here's the typical failure;

It's a 10 minute effort once the ECM is unbolted!

[almostordinary]

Hey gang, didn't want to leave another post on Pelican at a dead end.

Finally found the issue.

I decided to go after the rest of the fuel system over the last two weeks.

Everything at this point is new or less than a year old, so I decided to drain the tank.

And found what was clogging the strainer when I hit bumps or at intermittent intervals.

There was a lot of sediment inside, the tank isn't rusty, just somehow got contanminated with dirt/gravel.

Flushed it four times with old gas after draining the good gas, put a Bosch FPR that I had as a spare and cleaned the injectors.

Took it for a run, adjusted the AFR after a couple of runs and she is purring.