1995 Jeep 4.0 - lopes at idle - rich condition

1995 Jeep 4.0 - lopes at idle - Rich condition - High HC (1200) - won't pass emission test

- History:  1995 Jeep 4.0, 268,000 miles, started to lose fuel mileage and lope at idle.  Smelled raw fuel at tail pipe.  Will not pass emission test (high HC 1200).  I threw parts at it trying to fix ....  O2 sensor, crank sensor, MAP, IAC, throttle body (but had an air leak at shaft), coil,  wires, plug , new distributor..... nothing worked..... I finally decided it must be the low engine compression (95 psi on one cyl...110 on others) causing a poor burn and misfire, so I rebuilt engine.

Today - engine runs good.... buuuutt there is still a lope at idle and the idle is low. Does not stall.  Smell raw fuel at exhaust.  Once off idle, the engine runs fine.  I have been using a Pico Scope to try to find the culprit..... but am out of ideas.  The only thing I can come up with is that something is telling ECU that it is cold (so in a choke condition)....also, about the same time that I started to have the problem, the engine coolant temp gauge in dash quit working (note, on this engine, there are actually 2 coolant temp sensors, 1 for the ECU and 1 specifically for the gauge.... so this could just be a coincident... or maybe significant???).  My only other thought is its a CAN issue that I haven't found??

All help would be appreciated, I am out of ideas.  Any specific tests I should run?  Things to look for??

Have you checked for fuel being pulled thru the canister? Pull off the vapor line at the purge valve, is it wet with fuel? Another check, fuel pressure test, maybe a kinked, obstructed fuel return line to the tank?

What is the coolant temp sensor reading in scan data? Also maybe you have an egr valve stuck open if it has one

Thanks for responses for things for me to try....  My comment back to your responses:

Line to canister not pulling fuel.  Fuel pressure is a steady 40 psi with no drop at engine rev (within spec).  There is not a fuel return line in this system (but this was a good idea!).  

I don't think engine is getting hot.  I have used an infrared therm and it reads under 200 deg F...but I will see if my scanner reads coolant temp via the ECU.  I also purchased another aftermarket stand alone coolant temp gage and sending unit to be sure about my temp. This engine does not have an EGR in its emission system.

Any other ideas?  

I put a vac gage on it today  - reads 15-16 in at idle.  Could not detect any vac leaks.  Timing shows about 12 deg BTDC at idle...every once in an erratic jump in timing movement that bounces to about 16 deg BTDC.    RPM pickup on timing light shows 760 RPM at idle in neutral.  Still smell fuel at tail pipe.

You say this 1995 doesn't have a fuel return line?
I don't recall anything that old having a returnless system.
One way for extra fuel to get in the engine can be through a ruptured fuel pressure regulator (usually mounted on the fuel rail return side.) It can break inside and the vacuum line will end up pulling gasoline into the intake manifold.

Apparently 1995 was an oddball year for fuel pumps, 93 and 94 had a return system, but 95 is returnless. Pump is in the tank and must be regulated there too. However, I have (I think) good fuel pressure (40 psi). My fuel system has a single fuel supply line from tank (pump) and a single vac line at top of tank that goes to canister. Your ideas seem spot on, but my fuel system does not have those parts .... causing me much frustration haha.

I tend to think I have a fuel control problem, where ECU is getting bad info and triggering injection wrong... but I am guessing.

I appreciate everyone's thoughts on this... I am pulling my hair out on this one.

So..you have a transition year vehicle. A little bit of o.b.d. 1 and some o.b.d. 2, some call it o.b.d. 1.5. You mentioned you would check to see if scanner would read coolant temp., any info.? If it can't, I would get the motor up to temp., shut it off, put a jumper wire across the 2 terminals of the connector for the coolant temp. Sensor, this test will tell the e.c.m. it is up to temp. Start it back up. Give that a try and watch vacuum gauge while jumper is installed, report back with results

ok - connected my OTC 4000E - I can read ECT at 194 after warm up. I also discovered code 13 (no change) for the MAP. I know this is a new MAP! I erased code and re- ran. Code is clear for now. While playing with the Sensor tests, I discovered that if I test the MIDL (Minimum Airflow Idle speed) the RPMs will lowly drop and the engine will die. Does this mean anything?

Last, I checked the AFF (Adaptive Fuel Factor) and it is -9.3 also checked the AAF (Added Fuel Factor) and it is -204. I need to look up what those mean.... and if significant to my idle issue.

thanks for any and all help

Pull the vacuum line for the m.a.p. Sensor off, inspect it, collapsed? Clogged?

What is your MAP voltage KOEO and engine running at idle?
Those fuel trim numbers you posted are not how Chrysler displays them. I don't know what those numbers are.
You said you had 1200 ppm HC from the exhaust before the rebuilt. What are they now? And what are your other numbers? CO and O2 in particular

This returnless fuel system sounds very unlikely...
I like car-part.com to find used parts and figure out interchangeability of parts.
This 1995 Jeep Cherokee 4.0 fuel rail for sale clearly has a feed return and regulator.
According to interchange, 1993, 94 and 95 all have the same rail for a Grand Cherokee, Cherokee or Wrangler.
No where in service info for your Jeep does it refer to the the fuel system as returnless.
In fact, it mentions the regulator several times.

This returnless fuel system sounds very unlikely...
I like car-part.com to find used parts and figure out interchangeability of parts.
This 1995 Jeep Cherokee 4.0 fuel rail for sale clearly has a feed return and regulator.
According to interchange, 1993, 94 and 95 all have the same rail for a Grand Cherokee, Cherokee or Wrangler.
No where in service info for your Jeep does it refer to the the fuel system as returnless.
In fact, it mentions the regulator several times.

OK - some responses to comments:
-Map sensor line is good
- MAP voltage at KOEO - 4.6 v
- Map voltage at idle and warm - 1.9 to 2.0 v (fluctuates )
- I'm not sure about the Adaptive Fuel Factor (AFF) or Added Adaptive Fuel (AAF)...but they do show as -9.3 and -204 on my OTC 4000E....???? I'm trying to learn more about what these numbers mean
- I have not taken vehicle back in to get new exhaust data... soon
- returnless fuel system.... not much to say except, I do have a 95 and it is a returnless system...maybe it was changed? I got vehicle years ago with 75k miles from original owner.... I don't think it was changed and I have read other forum comments about returnless systems on a 95 - I do agree that 95 was a weird transition year, because I have found other oddities that are either found on 94 or 96 models...???

I made three new discoveries today: 1) I only have vent air at defroster... so must have a vacuum issue at dash switch that I need to track down - I don't think this is the idle problem culprit, since all my vent position worked before with the idle problem present...but I will track down and fix 2) if the vehicle is rolling (whether in drive or Neutral) the idle will not drop off and stumble... this is the case as I coast in neutral down to a stop... but once stopped, the idle will drop and start to stumble. 3) my tach reads low..about 400 RPM (I need to set up scanner again to get a good number)... not sure if ECU takes any data from dash tach... or if ECU feeds dash tach... but my OTC scanner shows idle fluctuating between 640 and 740 RPM at idle.

I am not sure what all these clues point to... I am relying on more experienced and brighter minds than mine... thank you all for your help.

I checked forums also, many upset people getting the wrong fuel pump for a 95. Naxja.org has some info. Here's the kicker, return line system is 39 psi, returnless is 49 psi. I think you posted 40 psi on yours,?

Hmmm 95 Model seems like lots of variations and conflicting info - I just looked at FSM for 95 model and it quotes 39 +- 2 psi for returnless system... (who knows what is correct..)

- I did disconnect vac line to the vapor cannister and plug manifold for a test - intake manifold vac went to 18 in (was 15) at idle. I watched the AFF (was at -10.3) and ran RPM up to about 1500 for about a minute..AFF started to go back up to -8.9.... I ran the RPM up a little more to around 2000 and the AFF went to a +22 !! so I took it out for a test drive. Still have the low idle and lope ..... When I got back I connected OTC 4000 again ...AFF right back at -10.3 at idle - connect vac gage to intake manifold and right back to 15 in (this is with the vac line still removed from cannister) Either this Jeep or I am cursed.... what am I missing here? my thought now is to start over and do a relative compression test... scope the O2 sensor...IDK... more research


thanks all for your help and comments

RE: 1995 Jeep 4.0 and OTC Monitor 4000E: Can anyone tell me more or explain Adaptive Fuel Factor (AFF) and Added Adaptive Fuel (AFF)? How do these relate to Long Term Fuel Trim and Short Term Fuel Trim? What values should I be seeing? I have found very little info on these on the web.

thank you

OK guys - I have some more info on this problem - I scoped the No 1 injector and a parade of secondary ignition - the ignition patterns do not look right... please comment - next I scoped the No 1 injector and the No 1 plug wire (secondary ign).... they do not align with each other. It looks like the No1 plug is firing on No 6 ????? Next I moved the scope pickup from No1 plug to No6 plug.... this looks aligned with No1 injector,,,,,?????? so is this engine either firing or injecting fuel 180 degree out of phase???? How does it even run? It starts right up, revs pretty clean but lopes at idle when in closed loop. Please comment and help.... I am at a loss

04300EXC wrote:

I scoped the No 1 injector and the No 1 plug wire (secondary ign).... they do not align with each other. It looks like the No1 plug is firing on No 6 ????? Next I moved the scope pickup from No1 plug to No6 plug.... this looks aligned with No1 injector,,,,,?????? so is this engine either firing or injecting fuel 180 degree out of phase???? How does it even run? It starts right up, revs pretty clean but lopes at idle when in closed loop. Please comment and help.... I am at a loss
 

Port injection engines do not fire the injectors at the same time as the spark plugs fire. The Injectors are, usually, fired during the intake stroke.

Direct injection engines fire injector during the compression stroke.

 

Your sample rate is too low. Set it to, at least, 1MS/s.