5.9 magnum issues

Lee

Lee

ECGS
Joined
Mar 20, 2005
Location
Louisburg NC
I just recently replaced the engine in my 1995 Dodge Ram. Having a few problems with the new motor that are stumping me.

It runs like a scalded dog down low when on the throttle heavy, starts cutting out at around 4500 RPM's like it has hit the rev limmiter (rev limiter is at 5200)
-If you are easy on it around town it runs fine untill it goes into overdrive and then it will start missing
-Seems to be the most of the problems seem to come from light throttle under heavy load
-when you put the truck in reverse it surges and runs like ass, only in reverse, not in nuetral or in any forward gears.
-cruising out on the inerstate if you let it go into overdrive it surges and bucks like crazy occasionally, not always, but maybe every 2-3 miles.
Occassionly when pulling up to a light the RPM's will surge and then the truck will die

A little info

Motor built by Poteats Engines in Kannapolis NC
.030 over bore with magnum R/T cam and Heads
Mopar M1 Intake manifold
Ported throttle body
New ignition coil
New plug wires
new plugs
New ECT (temp sensor)
new distributor cap
new rotor
new fuel pump
Grounds are all good
Fuel Sync has been set to 0/1
Only code it has thrown was for the temp sensor and after replacement it has not thrown the code since (old sensor was broken)

Any idea's?

Gonna take a friend truck that is the same here pretty soon and try swapping some sensors and see if it makes any difference before I dump any more $$ into that does not seem to cure the problem
 
Im no dodge engine expert by any means so take my suggestion as a grain of salt but sounds like something in the air/fuel metering - mass air or a bad TPS sensor. Does it surge on idle?
 
I recently replaced the motor in my 99 and replaced the 5.2 with a 5.9...

It would idle great til i hooked up all the vecuumlines, then ran like crap.

EVERY time I put it into gear it would stall, or if it DID actually run, it backfired and ran REALLY poorly.

Looking underneath with a VERY qualified friend of mine we noticedthe Crank sensor wasnt bolted down tight....

It sits on the rear of the block on the passenge side and reads the flywheel when it comes around.... If the sensor is bad or the gap between it and hte flywheel is messed up anywhere, it can cause it to lose spark.

I had to replace mine, Auto Zone had them for $40.

Just a thought...

Pete
 
My first thought was also TPS... but looking at the list of mods.... I'm wondering if the computer can't figure out how to run it reliably. Is that a mass air motor? Does it do datalogging?

While I'm throwing around ideas... how's it shift? Like you'd expect, or harder than normal, at higher RPM (like it's in limp)? Just thinking about the closed-throttle decel stalling... I've seen that with bad speed sensors. The computer sees closed throttle on the TPS, doesn't know how fast the vehicle is going, and surges a couple of times before stalling.

Then again, that also suggests that the computer doesn't know how to manage the A/F on closed-throttle decel, because it's pulling more air than the maps say it should, etc.
 
It is a multiport engine, but not mass air, has a Map sensor. The map, IAC and TPS are all attached to the thottle body, gonna try swapping my friends throttle body onto my truck and see if it helps out.

Saf-t, shift same as always, hard as hell, but it has a Transgo shift kit and a tweaked valve body, so it does not help me much there, Problem is this is an OBD 1 engine, so having good diagnostics from trouble codes seems to be slim to none

Checked TPS voltage the other night, At WOT I had 3.6v and it did vary the voltage through the throttle range
 
CrayolaCJ said:
I recently replaced the motor in my 99 and replaced the 5.2 with a 5.9...
It would idle great til i hooked up all the vecuumlines, then ran like crap.
EVERY time I put it into gear it would stall, or if it DID actually run, it backfired and ran REALLY poorly.
Looking underneath with a VERY qualified friend of mine we noticedthe Crank sensor wasnt bolted down tight....
It sits on the rear of the block on the passenge side and reads the flywheel when it comes around.... If the sensor is bad or the gap between it and hte flywheel is messed up anywhere, it can cause it to lose spark.
I had to replace mine, Auto Zone had them for $40.
Just a thought...
Pete
Click to expand...

Not the CPS, would have never been able to set the fuel sync if it was the TPS
 
Drove around some today with the scan tool hooked up and watched the data stream, everything seems normal except for when the truck starts cutting out the 02 sensor flatlines to 0 v. Tried unplugging the 02 sensor to run the computer in open loop and see what the truck would do then, It still shows some readings and of course when unplugged the o2 sensor readings were all wacky and it threw a code, but when it would start acting up it still shows 0 volts on the 02.

Line of thinking was the 02 sensor was going to 0 volts to show a lean condition in order to get the computer to add more fuel (maybe bad fuel pump not allowing enough fuel?) So I hooked up the fuel pressure gauge and the thing stayed on 40 PSI even when the truck would start running rough and surging.

This thing has me baffled, MAP, TPS, ECT, IAC, all of them are showing normal readings, and the O2 is also untill it starts runnign rough and flatlines.
Pretty sure its not the 02 sensor though because unplugged it made no difference in open loop, truck still acting the exact same :confused:
 
Sounds like the computer. Usually when you unplug something the computer has a preset value that it uses. If it's still showing the o2 sensor is varying voltage, it shouldn't.
 
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