At idle RPM drop and feels like its about to stall

[TurboedMJ]

I will check. 

[OldSch88L]

On 8/10/2023 at 10:50 PM, TurboedMJ said:

How does it do at 2k rpm steady? Same issues?

It seems OK off idle through the rev range, maybe on the weak side... I keep comparing to my 2wd 2.5 Ranger, which has give or take the same power, and the Ranger is way peppier. Then again, it is SOHC and not pushrod, multi point injection, dual coils/8 spark plug head, less driveline parasitics losses, and smaller tires and super light Alcoa wheels. The Ranger runs 4.10 gears, while my 2.5 4x4 Comanche runs 4.56s and 31's. So I guess the lack of power feeling is normal. What I find suspect on the Jeep's EGR is its random opening and closing, compared to the info I found online...

[Ωhm]

Off Topic:

 

On 8/10/2023 at 10:07 PM, OldSch88L said:

Haven't found a vacuum leak yet, and all that data is from a 1988 MJ, 2.5L manual, with a 1986 manual 2.5 ECU

 

ECU pin C200_8 served two different purposes for different years, 1986 used it as a Wide-Open Throttle SW (WOT) while 1988 use it as a Power Steering Pressure SW (PSPS). I would hope the ECUs have different part numbers. Could affect drivability.

[OldSch88L]

7 hours ago, Ωhm said:

Off Topic:

 

 

ECU pin C200_B served two different purposes for different years, 1986 used it as a Wide-Open Throttle SW (WOT) while 1988 use it as a Power Steering Pressure SW (PSPS). I would hope the ECUs have different part numbers. Could affect drivability.

The ECUs DID have different part numbers, but couldn't find any info about differences between the two. And since the truck seemed to run fine at first with the 1986 ECU, that was the end of it. But I always felt like the truck ran better with the 1988 ECU, but I thought it was in my mind, as many weeks went by from the moment I fried the original ECU until I found the 1986 one and started driving the truck again.... What you're saying is really interesting, since using the REM, I set up my TPS on the dot according to procedure. The REM will tell me when it's closed throttle, part throttle, but never full throttle even with my foot almost denting the floor pushing on the gas pedal... I'll sure look into it!!!

[TurboedMJ]

On 8/11/2023 at 8:40 PM, cruiser54 said:

Is the EGR installed on the intake manifold?

Is there a plug in the intake manifold where the other end of the EGR tube would thread in? 

It has a '99+ plenum style intake manifold and a pacesetter 6-2-1 header. So no provisions for egr were made. 

[TurboedMJ]

Was just checking for a vacuum leak... This is my MAP hose. Think it has anything to do with the problem?

[cruiser54]

without a doubt.

[TurboedMJ]

I believe it fixed my issue? I'll have to put some miles on it and follow up. 

[tdtony]

I've been out of town the last few weeks, but I finally got a chance to work on the truck again.

 

Bought this EGR valve 

https://www.autozone.com/emission-control-and-exhaust/egr-valve/p/duralast-egr-valve-egr4458/28785_0_0

Blew air into it and it seems good. Installed it and I didn't notice a change.

 

I did tip 14, and adjusted the throttle body butterfly to .003" and it's seems to be idling worse.

 

I'll order the the REM some time next month and check the O2 sensor. Any other suggestions in the mean time?

[TurboedMJ]

Put some miles on it and my fuel economy is worse not better. The idle issue seems to have improved, although it still sometimes almost dies. What next? 

[TurboedMJ]

Only weak point now is injectors. I'm going to go with some of Trevor's injectors and see what happens. 

[tdtony]

Just got my REM in and I'm getting a "no injector 12v" error code.

 

Not really sure where to start trouble shooting that. Not sure if this means it's an issue with the injectors themselves, wiring, or something else.

 

Is there a way to back probe the injectors? Or should I check voltage some where else?

 

I recently replaced the injectors, they're refurbished Volvo 746. 

 

 

[Ωhm]

Taken from REM Codes Description on NICKs website.

 

ECU Codes
These codes come from the 4.0L ECU’s internal Power On Self Test mode. They only run once when the key is turned from Off to Run and can be a little unreliable.

 

No Injector 12V
ECU did not detect 12V on Injector feed wire.
-TIP: If this code shows with “KO Tests Not Run,” it can be ignored.

[cruiser54]

Closely inspect the harness from firewall to engine. 

[TurboedMJ]

If I still have the EGR relay, could that affect runability?

[cruiser54]

No

[tdtony]

On 9/2/2023 at 12:31 PM, Ωhm said:

Taken from REM Codes Description on NICKs website.

 

ECU Codes
These codes come from the 4.0L ECU’s internal Power On Self Test mode. They only run once when the key is turned from Off to Run and can be a little unreliable.

 

No Injector 12V
ECU did not detect 12V on Injector feed wire.
-TIP: If this code shows with “KO Tests Not Run,” it can be ignored.

 

Thanks Ωhm,

 

I don't know how I missed that page. That's exactly what I was looking for!

 

 

 

https://nickintimedesign.com/rem-codes-description/

Just putting the link for anyone else who might need it.

[tdtony]

I talked with Nick and he confirmed that I can ignore that combination of error codes 

 

"The 12v code means nothing since the KO test didn't run to even test the 12v circuit. If your jeep starts, you don't have an injector feed problem."

 

So back to the drawing board.

 

Using the REM to look at vacuum and RPM side by side, RPMs start off around 700, with 16"Hg of vacuum, after a few seconds RPMs drop to the high 400s and vacuum drops to 12"Hg. Then they both go back up to the starting numbers. 

 

what would cause the vacuum to drop intermittently like that?

[TurboedMJ]

Refurbished injectors from Trevor at skankfoot racing fixed my idle issue completely. Pretty sure I am getting better fuel mileage as well

[cruiser54]

NICE!!

[TurboedMJ]

@tdtony 

Where did you get your injectors from? Have you figured out your issues yet? 

[tdtony]

@TurboedMJ

 I got my injectors from CS Performance Fuel Injectors. Still haven't got the idle issue fixed.

 

I know you said new injectors fixed you're issue, but what else did you try? Maybe I missed something obvious

[tdtony]

I still haven't made any progress on fixing this, so I though Id post all the information I have and see if anyone has any insight or suggestions.

I'm new to working on cars so these are all assumptions I've made, and things I've read about on this forum and NAXJ

 

spark
    new spark plugs
    new wires

fuel
    pressure at fuel rail: 31psi
    new Volvo 0280155746  injectors from CS Performance flow rate matched

 

Let me know if there something else I should check with either the fuel system or spark plugs, but I assume its an air issue.

 

 

Air

    MAP Sensor is good

    I have replaced all the vacuum lines coming off the intake manifold, and capped them off individual to see if they were leaking

    replaced the EGR valve and tested it

    Adjusted the throttle body butterfly to  .003"

    tightened manifold bolts 

    replaced the IAC

    replace the O2 sensor

 

Looking at the REM, the ECU keeps sending a signal to close the IAC. This could be  because the IAC is not working correctly. I have replaced the IAC, but the new part could be faulty. I'm not sure what the proper IAC behavior should be. When I remove the air intake hose from the throttle body when the engine is off, I cannot see the IAC pintle and when the engine is idling I can see the tip of the pintle. Its at an awkward angle so I can't really tell if there's any movement at idle.

Assuming the IAC is good makes me think it could be a vacuum leak, because I've replaced and checked the vacuum lines and the EGR valve, I'm left thinking that the leak could be the manifold or throttle body gasket. I replaced the throttle body gasket when I cleaned the throttle body.

Please let me know if I've made a dumb assumption, or if there is something I am missing. I can get videos If that would help, let me know if there are any readings from the REM that would be helpful and I can provide those.

 

Thanks,

TDTony