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Sporadic dip or surge in idle


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@cruiser54 hey so I changed my thermostat today and finished eliminating my c101 today - I improved on the $#!&ty ground crimps by soldering all 6 ground wires together. I also eliminated the fuel injector power crimp and soldered that together. 

I reverified the MAP tubing - Airtight. and put a little sealant where it goes into the tb. 
 

 

overall, she feels like she has more power but it’s still running rich. 

 

here’s the weird thing. Idling in open loop, the o2 sensor reads about 1.1v. When it goes into closed loop and starts restricting how much fuel is being sent, the o2 reading actually goes down to 0.6v. I know it should be going up if it has less fuel...  I’ve attached a video and it happens at 2:20 mark. I also know it reads around 5v when fuel is cut which indicates the o2 sensor is working..., so there’s something weird going on here  Also, after driving and going into idle I see the O2 sensor reading is normally around 0.6v but creeps up to 1.2v.

 

I meant to pick up a test light to check d2-9 but haven’t yet. I know the heater element is working at some level because I can see my o2 readings change on startup quite quickly. Starts off at 5v and goes down to 1v or so over the course of 20-30 seconds while it’s heating up

 

can anyone make sense of that? Is something bad with my ECU maybe? I’m really hitting a wall here...

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2 hours ago, PhilisDiller said:

I meant to pick up a test light to check d2-9 but haven’t yet. I know the heater element is working at some level because I can see my o2 readings change on startup quite quickly. Starts off at 5v and goes down to 1v or so over the course of 20-30 seconds while it’s heating up

Sound like 02 Heater circuit is working as intended.

 

I've been staring at your MAP and VAC readings. I would think VAC should be around the 18.0"hg. Also during its attempt for CL, MAP/VAC change like the 02S voltage changes until ECU goes OL.

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5 hours ago, jdog said:

Quick question probably not relevant but what plugs are you using?

NGK ZFR5N all fresh and fresh wires too

 

4 hours ago, Ωhm said:

Sound like 02 Heater circuit is working as intended.

 

I've been staring at your MAP and VAC readings. I would think VAC should be around the 18.0"hg. Also during its attempt for CL, MAP/VAC change like the 02S voltage changes until ECU goes OL.

My RPMs also creep up from ~800 to 1100 when in CL. I figured the vacuum change was due to the rpm change, but I will try to verify what vac I read while intentionally holding 1100 RPM. The idle seems to sound better and less lumpy when it’s creeping up in CL too. 

 

Also, I forgot to mention that the thermostat I took out was a 195 thermostat. Honestly, the coolant temp is about the same with the new thermostat. Any reason why she’d be running so cool now that we know it’s not the thermostat?

 

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50 minutes ago, PhilisDiller said:

Any reason why she’d be running so cool now that we know it’s not the thermostat?

RICH is a cool burn. LEAN melts metal.

 

With KEY ON only, note the BARO reading. BARO-MAP=VAC.

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On 1/3/2021 at 9:59 PM, Ωhm said:

RICH is a cool burn. LEAN melts metal.

 

With KEY ON only, note the BARO reading. BARO-MAP=VAC.

Key on Baro reading 29.6

Right on startup it runs really rough for a couple minutes - MAP ~19 and VAC~11

after warming up MAP ~15.5 and VAC ~14.5

 

It does look like the VAC creeps from 14.5 up to 16.5 or so when in CL before fail

when i hold the throttle to keep the RPM at ~1k RPM the vacuum doesn't move much VAC ~14.8

 

I'm not really seeing any movement in my O2 sensor now between CL and OL. sitting around 0.45v, but it never got really warmed up to full operating temperature.

 

I’ve attached another video showing what I read today. I’m seeing my IAC at <105 early on warmup and seeing it around <53 after it’s warmed up a bit. I’m not sure if that helps with anything. 

 

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Engine manifold vacuum (VAC) reading at idle should be between 18-21"hg. Now if engine runs rough due to excess of fuel or weak secondary ignition (unburnt fuel) I guess your VAC readings could be possible. I know you know your running RICH so where could the fuel be coming from? I think you asked this in your 1st posting, so if your not leaking fuel from the INJ's, Fuel Pump Pressure Regulator, EGR valve or the Charcoal Canister, maybe weak spark at idle. IDK. I don't like the VAC reading so I would also check MAP wiring.


Color Codes:
C218_A - BRN W/TR
C218_B - VIO
C218_C - RED W/TR


DVOM w/MAP disconnected, harness side.
C218_A - Continuity to GND
C218_C - KEY ON; MAP supply; 5vdc


818465760_C218MAP.jpg.718286a6e943dc85da0f923928529314.jpg

 

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Alright, so I verified the MAP harness and get the following

C218_A - 0.2 Ohm

C218_C 5.08V

 

looks like my c101 elimination dropped the resistance down from 0.8 Ohms 👍

 

I just tested the EGR and it completely dies when I depress the valve. I haven’t checked the open functionality, but because I’m having this issue at idle, I doubt that’s the issue. 
 

also, I adjusted my TPS to 16 by loosening the screws and adjusting the sensor. No difference in idle conditions. I will say my TPS only goes up to 87 according to the REM readout. 

 

I’ve run propane by every vacuum connection and near the intake/EGR. No fluctuations in idle. 
 

i reverified the fuel injectors by double checking unplugging the connection on each one of them while idling. Every one has the exact same level of rough idle response. 

 

the REM is throwing a code for fuel pump relay, but the previous owner already bypassed the relay. It’s normal to throw that code after removal right?

When I checked the throttle body valve, everything seemed to be working fine and everything seated nicely. Air filter looked to be clean enough too and there’s no leaves blocking flow through the intake within the grill.

 

coolant temp runs a bit low. New thermostat didn’t chant anything, but rich burn should be less heat. Intake air temp is really low. I should give this guy a replacing. Adding that to my list. 

 

okay so where I’m at, it seems like fuel should be good, air should be good. beginning to think this could be weak spark too. I have new plugs and new lightning wires. I have a new cap and rotor, but haven’t installed that yet and reindex it. I’ll give that a go and cross my fingers. 
 

It would be nice to try another ECU to see if it changes anything. I haven’t had any luck with renix XJ or MJ at my local junkyards in Durham NC. Anyone have one they’d be willing to loan me 😬
 

losing my mind with this thing. 

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58 minutes ago, PhilisDiller said:

the REM is throwing a code for fuel pump relay, but the previous owner already bypassed the relay. It’s normal to throw that code after removal right?

I don't get REM "throwing a code".

 

59 minutes ago, PhilisDiller said:

Intake air temp is really low. I should give this guy a replacing. Adding that to my list.

Keep this high on your list.

 

1 hour ago, PhilisDiller said:

It would be nice to try another ECU to see if it changes anything.

Yes it would be.

 

 

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I’ve attached a photo of the REM code. 
 

I cleaned the IAT sensor with electric contact cleaner. It looked spotless in the first place and made no difference. It looks like the PO changed out the sensor style at some point. Maybe this sensor doesn’t have the same temperature band output as the OEM one. See attached picture.

 

I also wanted to make sure my butterfly valve was adjusted properly and noticed that the adjustment bolt was snapped! Looks like I’m going to have to find a way to get that out and hopefully find one at a junkyard. 
 

1A92B4C8-569F-488E-A2AA-6F71FDF5AF71.jpeg.e23dbaae701b109d619a313d7a6dbd27.jpeg
 

 

439C3C56-6675-4287-80C3-12EF9FD6D074.jpeg

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Took a visit to NickInTimeDesign and sure enough "ECU CODES". No listing for "Fuel Pump Relay", but that could be just Website needs updating. Arrow down might mean LOW whereas arrow up might mean HIGH. Thank for opening up these new headaches for me. :laugh:

 

On 1/11/2021 at 6:07 PM, PhilisDiller said:

the REM is throwing a code for fuel pump relay, but the previous owner already bypassed the relay. It’s normal to throw that code after removal right?

When you say "bypassed the relay" do you mean that there's a jumper wire in place of the relay?

 

Also found this under RENIX PARTS SUGGESTION:

Intake Manifold Air Temp Sensor (IAT)
The stock IAT sensor has been long discontinued so we will need to adapt a similar sensor instead.

 

– GM part 213-190 will replace it but requires the intake manifold port to be retapped to 3/8″NPT (stock is 1/4″NPT) and replacing the pigtail connector as well. This will update the sensor to a currently used part with the correct resistance range.

 

@eaglescout526 Is this true, no NOS IAT sensors?

@PhilisDiller  1987 MJ 4x4 Shortbed 4.0 5 speed manual 

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oh sorry, I should have been more specific. You can go down one more row but it’s blank.

 

i believe it’s a red wire that’s had a little connector installed. There’s no fuel pump relay there. I’ve attached a picture of what I believe is the connection. 
 

thanks for hunting that down! Yeah, it doesn’t look like there are any renix sensors anymore. I believe mines already been tapped to 3/8”. What size thread does the HO IAT use? 
 

 

9938A1DB-4B69-40BA-838F-4686B52AEB6C.jpeg

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17 minutes ago, PhilisDiller said:

oh sorry, I should have been more specific. You can go down one more row but it’s blank.

Okay thanks. I'll forget LOW/HIGH.

 

18 minutes ago, PhilisDiller said:

i believe it’s a red wire that’s had a little connector installed. There’s no fuel pump relay there. I’ve attached a picture of what I believe is the connection.

RED usually means BATTERY FEED (Hot at all times).

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13 minutes ago, cruiser54 said:

They rarely fail and are easily tested. 

 

I've got a bunch of them. Used

what’ll you let one go for? 
I just double checked and it is a 1/4” NPT. 
 


It was actually a pink wire. Anyone know what color the fuel pump relay wire is?

1 minute ago, Ωhm said:

Okay thanks. I'll forget LOW/HIGH.

 

RED usually means BATTERY FEED (Hot at all times).

 

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I am looking for an orange with black wire. I see one in the harness where I elminated the c101. I also see a orange with black wire going into the EGR solenoid. I can’t find another one.

 

on the passenger side of the engine bay I see another one but none of them are single wire connectors. This is the photo I’m using for reference. My wires should be the color right?

 

 

386EA98C-677E-44D1-8171-AEDDA9404F73.png

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