[SOLVED] Idle RPM too low, stall, loss of power

[perpetualslack]

Hello all, I have a 1995 4.0 2WD with an odd set of three issues, it is my only vehicle since I my DD got hit on the highway last week.


SEE THE SOLUTION RUNDOWN HERE.

1)There is a loss of power at highway speeds, and when idling the truck will die cold, but not always die hot. Engine idles rough and bounces between 200-1000 (usually 200-400) rpm and has a signifigant loss of power above 2000. This issue occured very recently after I replaced an air filter
I have not be able to locate a vacumn leek yet, but I am hearing a loud woooommmm sound at highway speeds/ hum. Sounds like the upper intake is leaking air almost but I cannot pin down the location. Sometimes if the vents are on I hear a hum.

No error codes, runs extremely rich (I can smell the fuel out the tailpipe). There is a sound of a spark wire shorting (wires are good on another truck) at high rpms but can't track it down as a single person.

Clear flooded engine does not return a start, so no fuel leaking into chambers when off.

Things tested/replaced/repaired/id'd as an issue:
MAF - Replaced since original was bad, new one ok,stalls if unplugged
IAT - ???? Replaced due to age and snapped connector.
IAC - cleaned, stalls if unplugged
PCM/ECU does not show bad caps or damage
Bank 1 lean appears. The Sparks look fuel wet (replaced ~20k ago, copper sparks)
Wires have been replaced and are good
PCV passes shake test
PCV hose replaced
EGR line had hole sealed
Fuel pressure return vacumn return is not leaking
Fuel filter replaced (I think the fuel line connector side to tank is damaged - the plastic connector inside the line fitting is gone. No leak visible with UV dye.)
Fuel pump has issues (?see next major issue) of some sort, I think pump is old AND there is eletrical issue Replaced fuel pump
The fuel tank internal "gate" which blocks the nozzle entry is damaged (bent).
Breather hose to oil fill missing.
Exaust leak
Serpetine belt/tensioner has been replaced
All fluids drained and replaced (including differential)

2) There's an odd eletrical issue going on where the alternator voltage is unsteady (in part do to #1 issue), I think it is a bad connection somewhere but I cannot locate the issue. Previous alt had voltage regulator issues, replaced with new one which had the same issues (burned out). I am reading up to 19V on batteries at rpms >1000. The fuel pump also has a bad connection somewhere, sometimes it will refuse to crank and if I hit the relay box with a rubber mallet or bang on it starts just fine. No blown fuses.

3) I am having a blinking ABS and partially functional speedo. Tachometer (dash replaced with exploder) and live data on speedo read just fine. ABS is code 11 for low wire resistance detected. No unitentional ABS activations.

Minor, less important issues (if they might influence above):
A/C not cold when low rpm
Very slow coolant loss. Like I'm talking it'll slowly drain over 5+ months to empty but that feels relatively minor. Last cap was bad so replaced
Door chime intermittent
Power mirror driver side limited in adjustment (seems like someone forcibly moved it by hand)
dome light disabled due to shorting (fuse pulled)
Rear output shaft seal refuses to stay on since previous owner chipped it off with a flathead (the mating surface looks like a turbine fan)
Transmission is throwing up trans fluid to the cab floor via the shifter seal.
Tranny seeping out DRAIN plug.

 

[Bgunner]

"Breather hose to oil fill missing."

This will create unmetered air to be introduced after the mass air flow sensor (MAF). This will make the AFR to lean and cause idle issues among other things. Please find one and install as a first step and continue on with diagnostics. Also check the Air Filter Tube, goes from MAF to intake, these crack and let in unmetered air also.

"A/C not cold when low rpm"

This is normal and nothing to worry about in normal conditions, it is caused by the orifice tube size. Yes this can be changed to get good cooling at idle but raises the pressure in the system.

Sorry I can't be more help but this breather hose missing will screw up how the engine runs and a necessary piece for this engine.

 

[perpetualslack]

"Breather hose to oil fill missing."

This will create unmetered air to be introduced after the mass air flow sensor (MAF). This will make the AFR to lean and cause idle issues among other things. Please find one and install as a first step and continue on with diagnostics. Also check the Air Filter Tube, goes from MAF to intake, these crack and let in unmetered air also.

"A/C not cold when low rpm"

This is normal and nothing to worry about in normal conditions, it is caused by the orifice tube size. Yes this can be changed to get good cooling at idle but raises the pressure in the system.

Sorry I can't be more help but this breather hose missing will screw up how the engine runs and a necessary piece for this engine.

Bgunner,

I don't think, or at least I don't feel like the missing hose is the root issue, it was a gonner before this issue started occuring. I have it capped off/sealed right now after you brought this up since I could not find a good hose. All of them in the junkyard are toast. I tried getting a regular hose cut for it but the "lip" to the engine oil fill is too large.

Startup today is producing a new symptom. It feels like the exaust is missing/misifring? The beat of the exaust has about a quarter second missing in the puffs of exaust I get. Blocked cat possibly?

 

[Bgunner]

If you blocked off the opening to the intake tube and left the other open you will not have issues but if you block off the end of the oil fill neck it will cause issues with the PCV system.

To test for bad CAT remove O2 sensor before cat, use a compression tester hose as this will screw in and hook up a vacuum Gauge that can read up to 10lbs of pressure. If you get more than 2lbs to 3lbs of pressure the cat is getting plugged and needs replacement.

 

[perpetualslack]

If you blocked off the opening to the intake tube and left the other open you will not have issues but if you block off the end of the oil fill neck it will cause issues with the PCV system.

To test for bad CAT remove O2 sensor before cat, use a compression tester hose as this will screw in and hook up a vacuum Gauge that can read up to 10lbs of pressure. If you get more than 2lbs to 3lbs of pressure the cat is getting plugged and needs replacement.

I appreciate the help so far, I'll probably try and get that exaust leak fixed and see if it helps a bit, I can smell the fuel/exaust on startup and hot air blows in via the trans shift hole moving, so the leak is not minor.

EDIT: SHOP SAYS NO EXHAUST LEAK.
Also threw a bank 1 too lean code with breather hose plugged. Here's the data on hot idle ...idling about 600.

 

[Bgunner]

LT fuel trims are way off. Since the ecm is trying to give it more fuel but out of range to be able to it is throwing the lean code.

This could be caused by unmerered air entering the engine or fuel delivery issues. Most commonly it is unmetered air due to the intake tube being cracked. Did you check the tube I mentioned before?

Sometimes intake gaskets go bad and allow unmetered air in that way. Safest way to check that is use propane around the intake gaskets to see if the idle speed changes. If it does then there is a leak there.

Have you changed the fuel filter since purchasing? Could be clogged from bad fuel. Also do you have a fuel pressure tester? What does it have for fuel pressure with key on engine off, engine idle and lowest it dips to when cracking the throttle/reving the engine?

A bad O2 sensors can cause this also but it is far more likely unmetered air is the issue.

 

[perpetualslack]

LT fuel trims are way off. Since the ecm is trying to give it more fuel but out of range to be able to it is throwing the lean code.

This could be caused by unmerered air entering the engine or fuel delivery issues. Most commonly it is unmetered air due to the intake tube being cracked. Did you check the tube I mentioned before?

Sometimes intake gaskets go bad and allow unmetered air in that way. Safest way to check that is use propane around the intake gaskets to see if the idle speed changes. If it does then there is a leak there.

Have you changed the fuel filter since purchasing? Could be clogged from bad fuel. Also do you have a fuel pressure tester? What does it have for fuel pressure with key on engine off, engine idle and lowest it dips to when cracking the throttle/reving the engine?

A bad O2 sensors can cause this also but it is far more likely unmetered air is the issue.

Thank you for your help so far.

Intake tube is fine (aside from the plug I put in earlier). I am going to try and grab one from a junkyard to swap out and test.

I strongly suspect an intake leak. It was much colder where I worked in the winter (like -20F), it is now around 80F+ where I am now. Earlier today I hear a loud woooshing noise at high speeds and a loud hisssing noise at idle coming from center of the vallery of the block below the intake manifold. Unknown if intake manifold or intake plenum. I spray and spray, no response to idle. This is also circumstanical in that the rough idle gets better after warming up (a fuel delivery issue would be consistent).

Fuel filter has been changed recently, however I noticed the connector to the fuel pump from tank is missing a plastic piece in the center, but no visible leaks to the eye.

There is a visible fuel pressure issue on cold start. I am replacing fuel pump soon as it is appears to be failing, not holding pressure after about 1 hr. FPR is fine.
Edit: Low gas sensor is also no longer indicating for some odd reason.

To conclude:
1) There is likely a leak of either the intake plenium or the lower intake gasket
2) The fuel line from tank to filter is damaged
3) The Fuel pump is not holding pressure.
4) O2 sensors need a change since it's been 20 years.

Is there a test to determine the lower intake vs the plenium?

 

[86_FX4]

LT fuel trims are way off. Since the ecm is trying to give it more fuel but out of range to be able to it is throwing the lean code.

This could be caused by unmerered air entering the engine or fuel delivery issues. Most commonly it is unmetered air due to the intake tube being cracked. Did you check the tube I mentioned before?

Sometimes intake gaskets go bad and allow unmetered air in that way. Safest way to check that is use propane around the intake gaskets to see if the idle speed changes. If it does then there is a leak there.

Have you changed the fuel filter since purchasing? Could be clogged from bad fuel. Also do you have a fuel pressure tester? What does it have for fuel pressure with key on engine off, engine idle and lowest it dips to when cracking the throttle/reving the engine?

A bad O2 sensors can cause this also but it is far more likely unmetered air is the issue.

If you don't mind, (not trying to hijack a thread), could you drop some basic knowledge about what trims we should see/expect if you're experienced in it? I made a new post in 4.0 forum to avoid hijacking and would appreciate you chiming in. I understand exactly what you're saying but don't know how to relate it to my live data/scan tool.

 

[perpetualslack]

If you don't mind, (not trying to hijack a thread), could you drop some basic knowledge about what trims we should see/expect if you're experienced in it? I made a new post in 4.0 forum to avoid hijacking and would appreciate you chiming in. I understand exactly what you're saying but don't know how to relate it to my live data/scan tool.

I don't mind. It would help with isolating my issues.

Hello folks, what is this line called circled in yellow-orange? I have a leak somewhere on this line, I suspect the 90 degree rubber boot is faulty. Anyone know a fix or where I can find a new boot? Unplugging and blocking this makes the engine without a visible bad idle (you can still see it bouncing on the OBD scanner). Previously the line to the EGR broke and threw a EGR insufficent flow error on the GREEN line, I patched it with sillicone hose as you can see.

 

[SenorNoob]

You should be able to get an assortment of the little rubber fittings and even the plastic line at any parts store in the HELP section.

 

[perpetualslack]

You should be able to get an assortment of the little rubber fittings and even the plastic line at any parts store in the HELP section.

No luck on those fittings in my area (neither advanced, O Riley, Autozone, NAPAetc), there are two lines that run from them. I tested the boots for leaks and pressure test the vacumn lines and patched the lines.

I have been unable to replace the fuel pump due to rusted out bed bolts so far. I will update back with pressure test once the pump is replaced. Fuel pump and the FPR (Still no fuel in vacumn line) are my two biggest guesses right now.

EDIT: Fuel pump replaced and the low fuel pressure is gone. FPR is likely bad, plugging the FPR vaacumn line prevents rough idle. Maybe a intake leak?

 

[perpetualslack]

Solved!!!
Thank you for everyone's help (especially @Bgunner) . I have located the source of this tricky issue. Now I have a high idle There were five problems causing this:

1) Fuel pump check valve was going bad causing pressure loss and insufficent pressure.
2) Transmission fluid incorrect fill capacity*
3) Intake plenum leak (to be resolved soon) - High idle related
4) Vacumn/fuel leak on the Fuel pressure dampener hose. - Fuel was leaking out the oring on the FP dampener and into the intake valley.
5) Bad breather hose causing extra air and lean idle.

*I am having a possible transmission issue (see thread here). After replacing the fuel pump, I noticed a leak on the slave clutch, a drain and fill of transmission fluid solved the issue. The transmission had about 4.25 quarts (3.25 quarts is max for drain and fill).