Well,

Replaced my computer, in hopes, that it would fix my idle problem during closed loop. After doing research, when the truck is in closed loop, it polls the crank sensor, iat sensor and coolant temp sensor.

Currenly have a NAPA ECHLIN? crank sensor in there, when running under 180, the RPMS fluncuate between 300 and 1200 irraticly.

Ordered a MOPAR crank sensor today, going to install it tommorrow, and I am hoping that it was just a cheesy aftermarket crank sensor.

Sound like I got luck?

 

when i've had fluctuating/surging rpm's at idle, my problem has always been the TPS.

 

Sounds like a TPS sensor problem. A faulty crank sensor will cause a no start or a misfire.

 

Which would also cause backfiring? My truck sounds like a shoot range until it gets to about 160. Below 160, I can't hit the gas or the unit bogs out and dies. t 160 I can finally get it to 4k, let the temp guage go to 180 and it goes away.

I've posted this before and it was the crank sensor. I don't see the TPS causing this problem. And once it is at 180, idles like a champ (734 RPM).

 

no - a TPS won't cause backfiring.

backfiring into the intake or into the exhaust manifold indicates either a timing problem, where the spark is firing when a valve is not closed, or a valve closure problem. combustion chamber is supposed to be sealed when the spark fires.

timing is generally controlled by crank and cam position sensors. i don't know much about this, but the fuel sync is also a computer controlled function. if its not right, all hell occurs. you might need to have that checked/set by someone with a scanner tool. mckenna wrote some long posts recently about the importance of checking/resetting it whenever a crank or cam sensor was replaced.

 

Agreed on the no to this statement. There is a difference between a misfire and a backfire and there is a difference in the causes of each condition. A "miss" happens when a given cylinder does'nt fire at all. A backfire happens when the cylinder fires at the wrong time.

 

I have a new crank (napa) and cam (mopar); re-synced it with my snap-on. If this crank sensor dosn't fix it, I am going to double check the sync with the DRB 3 at work.

That;s why I am thinking that the crank sensor is bad (aftermarket sucks). Wouldn't be a valve closure problem (just pulled off the valve covers, recent valves done), timing chain isn't an issue (just did, timing is dead on) and according to the engine, the fuel sync is at 0.

Here is what I have done.

When I got it, she didn't run PO said it was timing chain.

So I replaced timing chain, messed up the timing, so pulled the heads 16 new valves and 16 new pushrods. After that, wouldn't run at all; diaged it to be a bad crank sensor. Replaced, still did it, but now to 180. DRB 3 at work scanned saying bad cam sensor, replaced that. Helped it a bit, still backfiring.

Once it hits open loop, it smooths out and runs great. It's only doing this during closed loop, so I thought for giigles i would try computer, replaced that with no success.

From cmkenna's posts on this forum, I have deterined the only sensors used during warm up are the crank, the intake air and the coolant temp.

Intake air and coolant temp work as required by testing, but the crank sensor flunkuates and the spark advance by the computer is approximatly 30-50 degrees, which is the cause for the backfire; IAC will hang open too, as the PCM is telling it the rpms are 300 then 1200 then 400 then 800 then 300 then 1200 then 500, etc.

No codes except exhaust too rich (it pours gas out when its in closed loop, legit the gas steams from the exhaust) and trans temp over. o2 won't affect closed loop, so I am not too worried about that. During closed loop, ti runs on pre-set values.

 

a valve closure problem would probably remain consistent and likely not change between cold engine vs warm.

post back what you find.

what kind (and how expensive) of a scanner does it take to check/set fuel sync. i'd like to have one for the tool box...

 

You stated you had an RPM fluctation problem, that's a sure sign of a faulty TPS. AGAIN, if crankshaft sensor is not reading, you WILL have a no start/no run issue, or if your lucky you will have a miss fire. Are you throwing a CEL?

 

Once it is up to temp, it runs fine. I at home have a snap-on solus, that's about 4 grand. At work we have a DRB 3. Not sure what else will do it.

Don't quote me, but I think a Genisys can do it too (we have one at school), I think they run under $2 grand last time I checked: http://genisysotc.com/ eBay has one for $1,600 (http://cgi.ebay.com/ebaymotors/ws/eB...#ht_4647wt_732)

No, I was reading what the computer is reading for 'RPM's, the motor might have a slight give or take 100 rpm flunctiation. TPS tests fine (works within limits), P/O replaced it and I tested it as an option.

By my scanner, you an see it running like above, the computer thinks there is an RPM fluncuation but there isn't, I guess I wasn't the clearest about it The motor will run from 600-750, but when you hit the gas it stalls out. During this time, it backfires and misfires, correct does both, and it sounds like a machine gun.

What gets the RPM readings for the computer? The crank sensor; so it could be a pheasable replacement. It's already ordered, but I wanted to post here in-case I missed something.

I have to let it warm up, on average, for about 22 minutes then it runs fine and I drive it,