Slight misfire, hesitation at moderate speed.

[TheRoger]

Hello.  Having a slight misfire/hesitation when travelling around 45-55 mph and i try to accelerate. It is intermittent and happens most often going uphill, though not always.  had the same probelm before, changed the plugs and wires, fixed no problem for about 6 months.  Same thing came back now.  swapped wires 4 and 4, still did it.  Swapping coil packs from a running parts car i have, still does it.  No codes at all on pcm.  Tried cleaning EGR, which was not too dirty and moving freely, still the same. Just wish i could troubleshoot right now so i can fix it, anyone have anything similar? Dont want to start throwing parts at it.      

[BodybyFisher]

No codes....hmmm

this sounds like a torque convertor clutch shudder, but that is not a common complaint, nor do you have a P0741 code that would indicate excessive slippage.  

Have you changed the tranny fluid?, is the fluid burned how does it smell?

this could be a fuel pressure problem also, if you can get a fuel pressure gauge with a long enough hose, tape it to the windshield and watch it when the problem occurs.  If you cant reach the windshield, check the fuel pressure with the key on, engine off, then idling, then at 2000 rpm, record pressure and let us know. 

Next time it happens drop the tranny down to 3rd out of drive to keep it from going into OD and see what happens

Another test, put the selector in 2, and take it up to 60 and see what happens.  

[TheRoger]

I changed the trans fluid about a year ago when i bought the car.  fluid is clean and at correct level.   I dont think its trans, will do it occasionally when not in OD, Have done a WOT about once a month, works fine, no issues.   Will check spark plug gaps later today after work, then fuel pressure.  

[TheRoger]

also it will take the odd misfire at idle, or very low speed, so its not isolated to cruising at moderate speed, just most frequent and sustained.

[BodybyFisher]

You really should not regap plugs and reinstall them.  They are encapsulated with an anti-seize that is not effective after they are removed and if you reinstall them you risk them seizing.  I hate to say it but you need new plugs now if you remove them.  What did you gap them at?  Did you have oil or water in the spark plug ports?  I doubt that you have a bad plug.  You do not have a misfire code.

One possible problem that I see is possible is that its tricky to get the spark plug cable snapped onto the plug, be sure each plug wire snaps onto the plug. But again no misfire code.

Now that you supplied more info it looks less like the tranny, you initially said 45 to 55 mph, like a shudder.    Now that it happens at idle that changes the diagnosis.

Keep in mind that if you are not getting codes like misfire or lean codes, and that complicates the problem.  Any misfire should set a code.  A bad fuel pump or restricted fuel delivery would set a lean code as the engine would be starved.

Does the check engine light ever flash while the misfire happens?

Are you sure you dont have ANY P codes?  You know you can check them through the dash?

[BodybyFisher]

I just remembered something.  We had a member who had a similar problem.  It drove him crazy.  When he found the problem it was shocking that this part could cause it.  I think I got your problem nailed.  He described it as a "fish bite".....  see the link below, we focused on TCC, but after extensive diagnosis it was the EGR pipe.  The EGR pipe is an aluminum pipe that cracks easily, I had one crack when I did an engine swap back in October.  Check it carefully, it screws into the rear exhaust manifold down below the EGR valve.

********************

Here is the thread by Kens96 that I was thinking about, he and I went through a LOT of diagnosis finding a stumble in overdrive. This would be a good thread to review, the key posts begin at #45 but a full read will be informational

http://caddyinfo.ipb...showtopic=18568

Here is another thread that I looped back to Kens fish bite problem.  I dont think the owner really dug into the problem and at the time I didnt know how easily these pipes crack.  The fact that you dont show codes is important

 

[TheRoger]

Hey great thinking!!! I checked and cleaned my EGR vlave clean but not the pipe.  I also get an occasional exhaust odor in the cabin when i pin the gas, could all be related.  A fishbite senstation would describe it well, Just got home now will check her out and report back.  I was just thinking ignition parts because the symptoms were identical when i had a bad wire previously. 

[BodybyFisher]

11 minutes ago, TheRoger said:

Hey great thinking!!! I checked and cleaned my EGR vlave clean but not the pipe.  I also get an occasional exhaust odor in the cabin when i pin the gas, could all be related.  A fishbite senstation would describe it well, Just got home now will check her out and report back.  I was just thinking ignition parts because the symptoms were identical when i had a bad wire previously. 

Fantastic!!!!  If you are getting exhaust smells in the cabin, check that pipe.  

Idle the engine and put your head down there when you gun the engine and listen for exhaust leakage sound.  

I may have the pipe in my Northstar part box because I wanted to save it for something like this, Ill look

Keep in mind that any exhaust leak, even the manifold gaskets can cause problems but that pipe being cracked or leaking is a good start

[TheRoger]

hey i just checked it out, seemed ok but theres no way to tell, the pipe appears to be brass, has a stainless or aluminum heat shield around it that moves.  Runs from back of EGR down to the manifold.  I have another higher mileage running parts car, could use that for a donor.  How in the hell can somebody chage that part it looks like a very diffcult job.  heading back out to listen for leaks there now.

[BodybyFisher]

Put your hand down there when you gun it, not close so you get burned but see if you feel exhaust.

I am not 100% certain, but an air leak by the O2 sensor will cause air/fuel problems also because the O2 sensor detects oxygen, I just dont know if it would cause a fishbite.  If you watch the O2 sensor output however in real time, it constantly changes and I can only imagine that a burst of oxygen could cause the air/fuel ratio to react on a short term basis.

[TheRoger]

hey i just checked it out.  Pipe appears to be in good shape, no sound or noticable feel of exhaust.  get a bit of a sucking air sound from the intake manifold area, could it be a vac or manifold leak?  I actaully dont mind working on these cars so much, but troubleshooting them is a pain.

[TheRoger]

could it be a failed EGR valve?  I am going to head to my shop and grap the other vlave and replace see if thats it.

[BodybyFisher]

Check all hoses for cracks and listen carefully foe vacuum leaks.  Take the beauty cover off to see.  

My guess however is that its not a vacuum leak as you would have a ranging or high idle along with lean codes.

I also doubt its the egr, it would set code.  If air leaked at its gasket, you would get a lean code, but did you replace the gasket?

You should check that egr pipe carefully, it may suck air in better than exhausting exhaust out.  There is a bolt at the top, back that bolt and and gently pull that pipe back and feel it for looseness or cracks.

[TheRoger]

no i didnt replace gasket it was in good shape and seals up fine.  The 'puff of air' noise is happening when i pull the throttle and appears to be comming from the area below tha black cylinder bank toward the area where that EGR pipe is, after listening for it.  Cant locate and exact source but its in that region.  Where does the black plastic hose that attaches just below the EGR hose go to? 

[TheRoger]

just read back that post you copied that is the EXACT symptoms im having so it must be related.  Any idea of a good way of changing that pipe?  I tried crawling underneath to see the bottom portion, nearly impossible to see anyhitng.  From the top it appears ok cant see any sign of damage or wear even but you never know.  "air puff' soound appears to be coming from that area.  

[BodybyFisher]

Beautiful explore that!!

I can not think of any black vacuum hose other than those that attach to the cruise control, if yours has vacuum hoses, that might have changed, the 95 I just worked on had 2 vacuum connections

[BodybyFisher]

Take photos with the beauty cover off

[TheRoger]

Sorry my mistake those are the heater hoses from the water pump.  This is the hose in question the silver shrouded hosethat runs to the exhaust manifold.

[TheRoger]

this hose appears to be in good condition.

[TheRoger]

beauty cover's been in the trunk for a week now lol

 

[BodybyFisher]

I am not sure what the braided hose is.  Is it connected?  Is this connected to the fuel rail?, either feed or return? 

It looks like someone replaced the 2 heater pipes that wrap around the back of the engine with hose.  

That silver flexi pipe is the pipe that cracks, check it close.  Remove that bolt and pull that pipe back and see if its cracked.  

[BodybyFisher]

Reread my prior post, I edited it a lot

[TheRoger]

hey pulled it back it isnt cracked at all its in perfect shape

[TheRoger]

seems solid as can be down below

[BodybyFisher]

Hmmm

Track down that air puff sound

What year is this car?