can any1 plz help?! 97 ram 1500 5.9L v8,
starts & runs great in open loop, as soon as ecm goes in2 closed loop the engine randomly misfires. tap the throttle, misfiring stops until the engine is shut down & restarted. ive replaced both o2 sensor, IAT, ECT, MAP, TPS, CKP, CMP, catalytic converter, FULL tune up. all stealership parts.

 

forgot to mention, fuel pump wuz replaced too. stealership part as well.

 

whats even more messed up is that i called Star techline, explained what wuz goin on, they told me my only route to go is "replace parts until the problem is solved." NOT ACCEPTABLE! @ this rate the only thing left to do is regasket the intake, but if the gasket wuz the prob, shouldn't it continue to misfire after the rpm's come back down & vacuum builds back up?

 

Did you route the plug wires per the service bulletin? Have you fixed the plenum yet?

 

yes. per TSB on Alldata. have not regasketted the plenum yet. y would the misfiring stop completely after the throttle is tapped?

 

The vacuum leak caused by the intake could cause your issue. I almost suspect an electrical culprit as well, but only slightly. I admit, your terminology of closed loop 1 & 2 throws me off a bit. Must be a regional thing. The miss-fire after a bit of run time makes me think that something that either closes a vacuum leak when cold, or connects a molex firmly when cold, then heats up, expands & causes a vacuum leak or a bad electrical connection is to blame here. Electrically, I would suspect a coil, battery connection, or nearly any major electrical junction. As for vacuum, I would say the intake plenum as mentioned above or a vacuum hose. On older carb powered cars, I used to use a can of spray starter fluid to find a vacuum leak. I did this while the engine was running then I slowly sprayed a suspected hose or area for a few seconds, if the engine revved higher, I found the vacuum leak. Just be careful because that stuff is very flammable. I hope this helps.

 

Your coil isn't yeller is it?

 

open loop & closed loop operation are 2 modes used by the ecm. battery test good voltage/load. connections are clean and tight showing no voltage drop across contacts. the coil has been supposedly replaced by the stealership as well, its not yellow. y would the engine run normally after a throttle tap? if it wuz the gasket under the plenum, wouldnt the engine run bad period?

 

no. the coil is not an accel. ive sprayed all over the engine for poss vacuum leaks, checked all vacuum hoses/plastic lines. no external leaks.

 

Because when you step on the gas, the PCM richens the mixture to offset the additional air it sees coming in. If the miss comes back when the engine settles at some RPM.... a vacuum leak may indeed by the problem.