So the CEL keeps flashing and throwing a redundant P0305 cylinder 5 misfire. It's a 2000 XJ that had a cracked head when I got it. Put a new clearwater head on it, cranked right up, but been having this problem.

It seems to idle better after the exhaust is fixed, but now it will surge and buck/sputter when just cruising down the road under load keeping enough throttle to keep going with the speed limit / traffic but if i give it more throttle (say 50% to WOT) it runs pretty damn good. i'm stumped.

- got the exhaust manifold flanges fixed and tight so no more leaks and replaced midpipe and muffler where there were holes

- new spark plugs

- tried some 4 hole taurus injectors, misfire stayed on cylinder 5 (got some rebuilt ones coming from Programbo)

- cleaned IAC

- voltage on injector wiring reads the same as the others when firing

- coil pack seems to be firing from injector 5 boot


Theres a coil capacitor that bolts near the oil dipstick mount on the passenger side, does that affect anything?

 

possible TPS?

 

Not too familiar with the OBD systems but I think the motor relies on just O2 after 50% throttle. Might be something to check into. If it's running great from 50%-WOT then whatever sensors the ECU uses data from to gauge fuel and air at 0%-49% throttle is where your problem lies. TPS is also a very good suggestion.

Again I have no familiarity with the system on your Jeep but I seem to remember something like that and it might help you diagnose your issue.

 

hmmm if someone could confirm that, that would be nice

thanks for the suggestion!

 

Whats the fuel pressure?

 

I was wrong...It's MAF readings (see below)


Open Loop Fueling

When you apply full throttle the ECU will transition to Open Loop Fueling where the injector pulse duration is calculated solely from MAF readings,the Fuel Enrichment table (desired AFR), and the LTFT value that has been stored for the last flow range (i.e. >40 or 50g/s). The Oxygen sensor data is no longer used (because it is not accurate under these conditions) as a feedback mechanism to correct for errors in the final AFR. If the value of LTFT is -10% then the injector pulse width calculated from MAF and desired AFR is further reduced by 10%.

 

ahhh. hmm, still got some troubleshooting to do then

 

Start with the basics:

1) Check compression. Could be a valve hanging up or a lifter stuck over-pumped. You should see that with a compression test.

2) Checked fuel supply by swapping injectors around. That's good.

3) Spark. Could be weak spark on that cylinder. Could be funky crank position sensor or cam position sensor. Swap plug wires. Swap coils if individuals.

4) Vacuum leaks. Maybe that runner didnt seal at the head? Or that runner has a vacuum connector running a hose to something with a leak. (I had this prob on a V8 where 1 runner fed vacuum to pwr brakes and the booster was leaking)

 

well. found the problem. cylinder 5 intake lifter has collapsed. head comes back off

 

Deep - what kind of vehicle are you talking about?

Jeeps don't use a MAF - MASS AIRFLOW SENSOR.

They use a MAP SENSOR - MANIFOLD AIR PRESSURE (Speed/density.)

All inputs are always used except at WOT, then it just gives max fuel pulse length..

 

yea, i knew we didnt have a MAF, i figured he was talkin generally though.