94 PAU - Actron 9185 readouts Question & help with misfire diagnosis

[happyreefer]

I have a 94 PA Ultra. question when reading my Short Term and Long Term Fuel trim specs with the Actron 9185 Scan tool.

The value is a 3 digit number with NO decimel points. eg. 162, I am unsure if this would represent 16.0% or 1.60%, does anyone have any information on this?

Also, I am trying to diagnose a P0300 random cylinder Misfire code.
Major hesitation when starting from stop or when in Overdrive starting to climb a slight hill. almost feels like a transmission issue, but DTC reports random misfire.

Code comes back with the Random Misfire, but when i use the data stream portion of the scan tool, Cylinder 5 seams be missfiring 90%o of the time.

-replaced plugs
-replaced wires
-cleaned MAF sensor with MAF sensor specific cleaner
-confirmed coil packs OK
-confirmed spark at end of wires.
-swapped injectector 1 & 5 and still same misfire on five.
-found vacuum leak on EGR tube between EGR and Intake. (discontinued part, fixed with JB Weld, pretty sure sealed the leak.)

Gary

[padriver]

I cannot help you on the fuel trim readouts, but regarding the misfire, I have had the exact same symptoms and it ended up being a bad EGR valve.

You should actually be able to verify this with the Scan Tool: It should show both the commanded EGR position and the actual EGR position. If you see any difference between the two, your EGR valve is bad and you have found the problem.

[maxwedge]

That scanner will not go that deep inot the diagnostics, same one I have. Can you short out #5 and check to see if the rpm drop is the same as an adjacent cylinder, sort of a power balance test. Also a non contact laser thermo pointed at each exhaust port will reveal a dead cylinder as the bad one will have a much lower temp reading., of course the rear is tough. Fuel trim is not important to pin down a misfire. Can you feel this misfire say power braking the engine? If it was lean enough to cause this condition you would get a code for that.

[Tech II]

Check compression?

[happyreefer]

thanks for the responses and ideas. agian. Code is P0300 (random Misfire) but in the data steam section on my scan tool, Cylinder 5 seems to be the culprit. I am not sure how to ground out the cyclinder as MAXWEDGE recommended. can you expand on your recommendation. Also, when you say power breaking, are you meaning, hold the break down and rev engine while in gear? as if I was going to smoke the tires? just confirming your comment.

-Compression checked: at least 145psi on all cylinders. all within 15% of the highest one.
-Changed O2 Sensor
-changed Ignition control module
-the Actron ScanTool does show the Requested EGR % and actual EGR %, both are equal

Uhgg!!!! Im done changing parts. think its gonna head to the shop soon.

[maxwedge]

Take rpm readings at idle or just above on any cylinder other than 5, then take the plug wire off see how much the rpms drop, then do the same thing on # 5 and see if the rpms drop about the same, if not that cylinder is not firing.

[happyreefer]

I have disconnected all injectors one at a time while the engine was running. each one appears to affect engine idle. when i say appears, I mean, it sounds like the engine sounds change when disconnected.

forgot to mention:
MPG are drastically lower since this has been happening.

[maxwedge]

Any misfire on an obd 1 car will cause a loss of vacuum, this can cause the engine to go rich. Seems as though from what you say the cylinders are firing evenly but that requires a lot of experience and feel to really tell the difference.

[imidazol97]

Do you get gasoline in the vacuum line for the fuel pressure regulator? After the car sits, what do you smell when you take off the line?

[happyreefer]

The test i did on the vacuum line for the fuel pressure regulator was this

with the car running, pull the vacuum line off the fuel pressure regulator and wait for 30 seconds or so, if fuel comes out that fitting, then the pressure regulator is bad. this was NOT the case in my test. also, just went out and smelled for fuel in the vacuum line with no smell of fuel either.

I think i will pull plugs again and accurately take compression readings again. will post results and get the consensus from everyone.

[happyreefer]

Ok, did another compression test. also noticed oil residue on the threads of the spark plug that came out of cylinder #6 and the same plug showed heavier wear on the white electrode portion than the other ones. these plugs maybe have 100 miles on them.

plugs (bosh platinum 2) and wires were the first items i replaced when troubleshooting this problem 2 weeks ago. car has 114K miles on it currently.

Cyl 1 169 psi
Cyl 2 175 psi
Cyl 3 159 psi
Cyl 4 170 psi
Cyl 5 162 psi
Cyl 6 165 psi

High compression 175 psi
15% of 175 is 26.25
175psi - 26.25 = 148.25 psi
- so my lowest cylinder is 159 psi well above the 148 psi threshold that would cause concern.

2012.12.16_14.41.43_23.jpg
2012-12-16_14-42-38_971.jpg

[maxwedge]

Back to basic diagnostics here, try and borrow or if possible buy a non contact temp thermo about 45.00, it will have many uses, get the engine good and hot when you are sure you can feel the miss check the temps on each exhaust port pipe, like I said the one signicantly cooler than the others is the culprit.

[happyreefer]

.:UPDATE:.

I cannot believe what i just found. after completing my compression test, I was putting the plugs back in. I noticed a small small crack on one of my ceramic portions of the plug. decided to run down and get a plug and replace it.

and everything is working as it should now. NO more Random misfire. I cannot believe i didn't notice the crack before this. I had the plugs in and out a couple of times over the last 2 weeks Ive been troubleshooting this problem.

Thank you for anyone that has posted on this.

Lesson learned.... triple check your spark plugs.