Saturday, March 3, 2012

Dodge Dakota stalls,stumbles at idle.has low fuel flow and runs hot?

Multiple problem with dodge Dakota vehicle.

This all problem started after engine rebuild.

First it was just stalling and stumbles off at idle.The engine fault was detected.Due to this engine rebuild was done by local car mechanic.
After engine rebuild all problems started and increased.
the fuel flow got less,car started running hot and stalling and stumbling also got increased.

As per this details the troubleshooting is as follows :-----

The fact that the fuel pressure goes up 2-3 lbs, can mean something, but it's to little of an increase to condemn a component. I'll need you to do a flow test. Pull the line from the throtle body. Unplug the electrical connector for the ignition coil, so we won't have spark. Attach a fuel hose onto the end of the line, and place the hose in a suitable container. Have an assisstant crank the engine, see how much fuel you get in 15 sec. A premeasured container always works best, empty quart of oil container (although technically it is not an approved caontainer). Do the test with the engine warm. If the flow looks obviously low, pull the fuel filter out, drain the fuel from it, and blow thru it in the direction of flow. You should be able to blow thru it easily, if not it may be partially plugged. If the filter is good, and we still have low flow, the screen on the bottom of the fuel pump may be plugged or the pump is failing. This can show good on a pressure test.

Also, when the stumbling occurs, have the aircleaner removed and spray a couple squirts of carburator cleaner into the throttle body, see if the idle wants to smooth out.

One more thing causing the problem is faulty throttle position sensor.  Test throttle sensor voltage by using a volt meter.

The throttle position sensor is a potentiometer that has three wires.
One wire is the ground that goes back to the engine controller.  Another is the 5 volt reference from the engine controller.  The last one is the signal return that the engine computer uses to determine the throttle position.  Usually the voltage will range from .5 to 4.5 V depending on the actual position of the throttle plate.  If you have less that .5 volts, the engine controller will assume the circuit is shorted to ground or open.  If it is more than 4.5 V, the engine controller will assume the circuit is shorted to power.  

The BLK/LT BLUE is the 5 V reference from the ECU, the V/O is the ground, and the OR/DK BLUE is the signal going back to the ECU.
See the diagram shown below :----

Also, when it is running and warm check for vacumme leaks around the intake manifold. You can liberaly spary carb cleaner around the intake and look for an increase in idle. It may be that when the engine is warm, warped surfaces of the intake or head are opening up, creating a vacumme leak.

Now, about the running hot issue. If you put a larger cam in, along with the other upgrades the engine could be creating slightly more friction and running warmer. This is typical of building engines and an auxilary cooling fan is needed to keep the temperture down in those conditions (traffic, high ambient temperature, going up a hill, etc). To test this and the stumbling condition we can do to things. Remove the t-stat completely and see how cool the engine runs, also see if the stumbling will subside. Do you have a large industrial fan, or access to one? If so, you can put a fan in front of it and idle, look for decrease in temp, and stumbling. I'd like to know how much less the stumbling occurs with the temperature drop.

Lastly, i'm concerned that the running hot is affecting the ckp, or reluctor wheel on the flywheel. It may be reaching the perfect temp to change the shape and cause an issue. The only way to tell would be to scope the ckp signal during the problem, and scope it when cold to see the difference in waveform.

Also, I believe a scope of the ignition system may be in order. Not to identify an ignition failure, but an ignition oscilliscope can reveal a fuel problem, an internal engine fault, or ignition fault. This is thru the kv (kilivolts) the ignition spark produces in each cylinder. The spark can be viewed, and a balnce of all cylinders can be determined as well. I didn't want to recomend this, because I was hoping we wold run accross something simple, but this test may tell us what we need to know. Another issue is, most (75%) of mechanics out there, do not know how to use a ignition scope. Most shops don't carry one, and if they do it's full of dust. You'll need to research shops in your area, and talk to the technicians, see if they understant how to evaluate vehicles with ignition scope readings. A good tech will take one look at the secondary cylinders signals and can tell you what the cylinder fuel mixture is like during combustion. If the ckp is causing a fault, the primary signal will be affected. If the computer's not controling the fuel injection, or the ignition coil, the scope can reveal this too. It basically will narrow down the problem to either fuel, compression/efficiency, or computer controls, or vacumme leak/ignition system or controls. With that information, we can take the tests that we've already done and see what to conclude.

This details will help.

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