86 2.5 Running rough/ stalling issue

[I_s2k]

Hey guys, so I’ve been battling a rough idle, situation on an 86 2.5/4 speed I acquired a little over a month ago. So far what’s been done…..

-new gas

-new fuel filter

-new map sensor

-rebuild throttle body

-cleaned off CPS at bellhousing

-cleaned all connectors and relays

-new cap/rotor/plugs/wires

-4 little vacuum lines have be replaced at the bottom of the TB

-cleaned all grounds bumper to bumper
-vacuum soft line to MAP replaced(was missing)

-New TPS

 

Id like to just throw money at it and replace everything but for now, this drivetrain isn’t staying and I’m wanting to swap eventually. I really just want to get it running with bare minimum put into it. The problem:

The Jeep will startup everytime no problem but will only stay running with MAP vacuum unplugged(very poorly obviously). It will even drive with it unplugged but starts to hesitate/sputter/bog when any hard acceleration is put down. When the MAP vacuum is plugged in, the Jeep will start and immediately stall unless I have the throttle depressed pretty far and even then it surges(no rpm guage but the the rpm will audibly go up and down slightly). With the vac line unplugged and the Jeep running, I can plug the hose and it’ll stay running but as soon as I plug it into the MAP it dies(it does this with both the new MAP and OEM MAP sensors). I’ve traced every vacuum hose and some are dry rotted a bit but aren’t leaking, the Jeep is relatively all OE still and I still have the OEM MAP sensor as well. My question is, the grommet on the brake booster is shot and I plan I replacing tomorrow but is this enough to cause this issue? Also, for the “EGR Solenoid” or whatever it’s called on the passenger fender that has the two relays for the fuel system, is that supposed to have 1 or 2 vacuum hoses attached? Mine currently has one but I can’t find any unplugged hoses. Any tips or insight would be appreciated. Thanks! PS: I apologize if any of my terminology is bad, I’ve had 6 XJ’s, all of which are 96+ and all were 4.0’s so the renix and 2.5 deals are new to me haha.

[eaglescout526]

12 minutes ago, I_s2k said:

My question is, the grommet on the brake booster is shot and I plan I replacing tomorrow but is this enough to cause this issue?

That unplugged would cause a high idle, course it’s an 86 so it’s an odd duck already because of how vastly different it is in the way the vacuum lines are run. So it could be but it won’t hurt to solve all the bad leaks and issues. 
 

 

13 minutes ago, I_s2k said:

EGR Solenoid” or whatever it’s called on the passenger fender that has the two relays for the fuel system, is that supposed to have 1

1. 
 

Have you done a compression test on the cylinders to rule out a bad head gasket?

 

How about the the front CCV? Is it plugged or does the little ball inside rattle freely?

 

I thought of another one. Have you tested the TPS and made sure it’s adjusted properly? 

[I_s2k]

3 minutes ago, eaglescout526 said:

That unplugged would cause a high idle, course it’s an 86 so it’s an odd duck already because of how vastly different it is in the way the vacuum lines are run. So it could be but it won’t hurt to solve all the bad leaks and issues. 
 

 

1. 
 

Have you done a compression test on the cylinders to rule out a bad head gasket?

 

How about the the front CCV? Is it plugged or does the little ball inside rattle freely?

 

I thought of another one. Have you tested the TPS and made sure it’s adjusted properly? 

I have not done a compression test but I can say that the oil is coolant free and vise versa for the coolant.

I have not checked either the front or rear CCV’s, they’re the weird canister deals. Do they just pull out like the plastic elbows thatre on the 4.0’s? Wouldn’t hurt to attempt in cleaning them regardless.

I forgot to mention that I also replaced the TPS and added that to the list of things done. How do you adjust them?

[eaglescout526]

16 minutes ago, I_s2k said:

have not done a compression test but I can say that the oil is coolant free and vise versa for the coolant

I had oil free coolant and coolant free oil but I didn’t have exhaust free coolant. I’d still check it just to be on the safe side as mine did the same thing as yours and it was due to a bad head gasket. 
 

Rear is hard to replace. I think there was some NOS around but i dont know anymore. I dont work at a mopar dealer anymore. Yes they do pull straight out and the grommets can be replaced. 
 

There’s a write up somewhere on adjusting them. I can post how later from my TBI manual. 

[I_s2k]

Just now, eaglescout526 said:

I had oil free coolant and coolant free oil but I didn’t have exhaust free coolant. I’d still check it just to be on the safe side as mine did the same thing as yours and it was due to a bad head gasket. 
 

Rear is hard to replace. I think there was some NOS around but i don't know anymore. I don't work at a mopar dealer anymore. Yes they do pull straight out and the grommets can be replaced. 
 

There’s a write up somewhere on adjusting them. I can post how later from my TBI manual. 

Okay I’ll look into it! Thanks and that’d be appreciated!

[I_s2k]

16 hours ago, eaglescout526 said:

That unplugged would cause a high idle, course it’s an 86 so it’s an odd duck already because of how vastly different it is in the way the vacuum lines are run. So it could be but it won’t hurt to solve all the bad leaks and issues. 
 

 

1. 
 

Have you done a compression test on the cylinders to rule out a bad head gasket?

 

How about the the front CCV? Is it plugged or does the little ball inside rattle freely?

 

I thought of another one. Have you tested the TPS and made sure it’s adjusted properly? 

Alrighty so I tested the TPS just now. B to C I’m getting 5v, I saw two different write ups on how to test but this one made the most sense to me since the readings were closer to what I’m getting. But anyways, B to C is 5v, moving throttle does not change this value and A to B is 4.91v WOT and 1.05v closed. I saw that WOT should be 4.6-4.7v for M/T. Gonna attempt to adjust it but I feel like this wouldn’t be enough to cause the Jeep to not stay running.

[I_s2k]

10 minutes ago, I_s2k said:

Alrighty so I tested the TPS just now. B to C I’m getting 5v, I saw two different write ups on how to test but this one made the most sense to me since the readings were closer to what I’m getting. But anyways, B to C is 5v, moving throttle does not change this value and A to B is 4.91v WOT and 1.05v closed. I saw that WOT should be 4.6-4.7v for M/T. Gonna attempt to adjust it but I feel like this wouldn’t be enough to cause the Jeep to not stay running.

Little update, got it adjusted to 4.65v WOT going from + at A and - at B. With probes is same terminals it’s also at 0.86 closed.

[eaglescout526]

15 minutes ago, I_s2k said:

Little update, got it adjusted to 4.65v WOT going from + at A and - at B. With probes is same terminals it’s also at 0.86 closed.

That sounds very correct. I got mine to fall in between the 4.63 and 4.65 just to be in the middle but its preference really. Your TPS was out of spec by a bit. The 5V being rock solid is good, ECU is outputting the correct voltage to the TPS. 

Now it shouldnt be getting more fuel than it needs to.

 

I once had a TPS do some funny stuff to me while driving. Idle would be either crap or not and driving would be great and then slow down and pick back up for no reason. Changed out the TPS and its been fantastic since.

[I_s2k]

1 minute ago, eaglescout526 said:

That sounds very correct. I got mine to fall in between the 4.63 and 4.65 just to be in the middle but its preference really. Your TPS was out of spec by a bit. The 5V being rock solid is good, ECU is outputting the correct voltage to the TPS. 

Now it shouldnt be getting more fuel than it needs to.

Sweet, like I’ve said before, these are all firsts for me but now I know for that’s not my issue. Jeep still won’t stay running unless MAP Vacuum is unplugged. Gonna start testing other sensors and seeing what I get as well as just once overing vacuum lines etc.

[I_s2k]

7 minutes ago, I_s2k said:

Sweet, like I’ve said before, these are all firsts for me but now I know for that’s not my issue. Jeep still won’t stay running unless MAP Vacuum is unplugged. Gonna start testing other sensors and seeing what I get as well as just once overing vacuum lines etc.

So testing the connector for the MAP, I’m getting 0.05ohms when connecting + to B and - to - battery terminal. The ground for this sensor(dipstick) has been cleaned and wire brushed as well.

[eaglescout526]

How about the block to the firewall? Bat to block?

[I_s2k]

2 minutes ago, eaglescout526 said:

How about the block to the firewall? Bat to block?

Wire brushed the nut, threads and block for the block connection as well as cleaned the strap. Also cleaned, wire brushed both ends of the strap and the bolt/firewall connection. Also just looked the front PCV. Cleaned it up a little bit and the little check in it moves freely. The rear one looks pretty nasty but I didn’t wanna spray anything up into it.

[I_s2k]

Anyone happen to know what this is? Seems like it’s broken or missing a spring.

[eaglescout526]

2 minutes ago, I_s2k said:

Anyone happen to know what this is? Seems like it’s broken or missing a spring.

Wide Open Throttle switch. This was phased out in 87 and used the power steering pressure switch to get the same reading to the ECU when it is in WOT.

I dont know what else used this switch, YJs had it from 87-90 but that still doesnt make it common to find. 

[I_s2k]

Just now, eaglescout526 said:

Wide Open Throttle switch. This was phased out in 87 and used the power steering pressure switch to get the same reading to the ECU when it is in WOT.

I don't know what else used this switch, YJs had it from 87-90 but that still doesnt make it common to find. 

Ah okay i figured it had something to do with something along the lines considering it’s placement, I'm not worried about it haha.

[eaglescout526]

That cannister on the rear of the valve cover appears to be a filter of some sort. I looked inside and I saw a bunch of wires that were in similar size to what you find on a wire brush. I sprayed some carb cleaner in it and the liquid came out brown.

[I_s2k]

9 minutes ago, eaglescout526 said:

That cannister on the rear of the valve cover appears to be a filter of some sort. I looked inside and I saw a bunch of wires that were in similar size to what you find on a wire brush. I sprayed some carb cleaner in it and the liquid came out brown.

Okay I’ll have give it a snort. Currently testing the MAP voltage. Now the engine is warm to the touch, like you can lay your hand on the valve cover and be comfortable with it. It’s currently reading 3.89 with + to B and - to A. I read it’s supposed to be 4-5v and between 1.5-2.1v hot. Is this MAP bad then?

[I_s2k]

Just now, I_s2k said:

Okay I’ll have give it a snort. Currently testing the MAP voltage. Now the engine is warm to the touch, like you can lay your hand on the valve cover and be comfortable with it. It’s currently reading 3.89 with + to B and - to A. I read it’s supposed to be 4-5v and between 1.5-2.1v hot. Is this MAP bad then?

Supply voltage to it is 5.05v with - to A and + to C.

[I_s2k]

Would also like to add that these are also unplugged and I have no idea what they are for. The 3 and the square one are all by the blower motor. The one by itself is below the alternator.

[eaglescout526]

First pic is hood light(red), second is the bullet connector for the 4wd light, third is the cruise control ground

Not familar with the second pic, I have the same plug on my XJ but it is for the automatic leveling system which the MJ never got. 

Third is unknown. I have it too and not sure where it goes. 

 

Not sure about the MAP voltage.

[I_s2k]

1 minute ago, eaglescout526 said:

First pic is hood light(red), second is the bullet connector for the 4wd light, third is the cruise control ground

Not familar with the second pic, I have the same plug on my XJ but it is for the automatic leveling system which the MJ never got. 

Third is unknown. I have it too and not sure where it goes. 

 

Not sure about the MAP voltage.

Ah okay gotcha, well if this thing had a good light it’s long gone and it’s a 2wd so that makes sense. This does have the load sensing brakes, is that what mean?

[eaglescout526]

Not all MJs and XJs came with a hood light. Chances are higher that it never left the factory with one. They were an accessory. I still have two left I am selling if you want to put one on.

 

2 minutes ago, I_s2k said:

This does have the load sensing brakes, is that what mean?

No. The XJ got a really cool accessory exactly like what GM put on their cars. Its an air compressor system that raised and lowered shocks based on the weight of the rear of the vehicle. Has nothin to do with the MJ brake adjustor in the rear.

[I_s2k]

2 minutes ago, eaglescout526 said:

Not all MJs and XJs came with a hood light. Chances are higher that it never left the factory with one. They were an accessory. I still have two left I am selling if you want to put one on.

 

No. The XJ got a really cool accessory exactly like what GM put on their cars. Its an air compressor system that raised and lowered shocks based on the weight of the rear of the vehicle. Has nothin to do with the MJ brake adjustor in the rear.

Oh wow I had no idea that was a thing. Cool to know thanks and I’m good, I don’t think I’ve had a vehicle that’s ever had one working or there haha. Gonna try and warranty that MAP sensor and get some gasket material and see if I can’t make the two gaskets for the EGR as those both look like they’re smoked.

[eaglescout526]

My XJ will have that accessory. Hopefully in a functional state and not just for looks haha. 

 

[I_s2k]

9 minutes ago, eaglescout526 said:

My XJ will have that accessory. Hopefully in a functional state and not just for looks haha. 

 

That’s awesome man! Ima look into that.