3.0 idles and runs rough, now backfiring
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06-21-2017
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Location: West Fargo, ND
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3.0 idles and runs rough, now backfiring
I have a 2000 Ranger XLT with a 3.0 that I just got last week. I knew it was running rough but other than that well taken care of and a good run around pickup for me. So I started working on it to get it going better and cant seem to figure it out. The guy I got it from said his son drove it for years. Well taken care of and no issues. One day it started to run rough, I would compare to a coil plug on a Ford V8 which led me to replacing sensors and electrical stuff. He had it in and they said it has low compression on 5 and 6, but told him the head gasket was fine. Since I got it, I replaced plugs, wires, now getting exhaust backfires, coil, IAC sensor, cleaned MAF and throttle body. It is very low on power and struggles to go from 40-70 in a couple miles getting on the highway. I finally got some codes the past couple days, all for O2 sensors. I ordered them along with injectors. It also starts hard, cold or warm. It does run pretty smooth past 1200 rpms but does have the regular backfires now. Should I keep going with this stuff or is it more than likely a valve or possibly cam.
#2
06-21-2017
Welcome to the forum
First, vehicle computers can NOT tell when a sensor is bad, in fact if you get a code and read the definition for that code and it mentions a sensor, then that sensor is GOOD or computer wouldn't know there is a problem
i.e. O2 sensor Lean Bank 1
This means O2 sensor IS WORKING, or computer wouldn't know Bank 1 was Lean
So "don't shoot the messenger"
Even though it is harder to do than throwing easy to get at parts at a rough running engine, compression test should always be first thing you do
Compression is black and white, can't be intermittent, it is either good or it isn't
So once test is done you know if it's the problem, so don't waste time and money on non-fixes
Or you can move on to spark or fuel issues
Remove all spark plugs when doing a compression test, you need fast crank speed
Cold engine is best, you can do warm engine test if cold test shows issues
3.0l Vulcan engine used 9.3:1 compression ratio so new engine should run 165-170psi
More miles 155-165psi
After testing all 6 cylinders and WRITING DOWN the results, there shouldn't be more than 16psi difference between highest and lowest, 10%
If a cylinder is low then retest to confirm
Then add a teaspoon of oil to that cylinder, use a straw in a bottle of oil to pull out oil then release it into the spark plug hole
Retest "wet"
Compression will always go up on a "wet" test, how much of a change can tell you if its Rings or valves that are leaking pressure
If you have two adjacent cylinders showing lower compression then there could be a head gasket leak between the two.
Put spark plug back in one of the cylinders then test other cylinder's compression
Then remove spark plug and test again, there should be NO change, one cylinder can't effect another unless there is a breach in gasket between them
You could just have a vacuum leak, that causes O2 codes and rough idles
After engine is warmed up and idling, about 800rpm
Unplug the IAC Valves two wire connector
IAC Valve will close and RPM should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leaks
If idle stays high then there is a leak
Coil pack wiring on Ford V6 is odd
One side is 1 2 3, the other side is 5 6 4, NOT 4 5 6
1 and 5
2 and 6
3 and 4
These are Match pairs and share the same coil in the coil pack
You also have an EGR system that opens an EGR valve to allow exhaust gases to enter the intake when accelerating, this cools the cylinders to prevent a spike in NOx gas, toxic gas
If EGR valve is opening to soon or leaking then engine will lack power, and would run rough
EGR Valve is opened by Vacuum hose attached to it, there should be NO vacuum at this hose when idling, only during acceleration
Pull off that hose when idling and see if engine smooths out, and that the hose has no vacuum present
Backfires are usually caused when a cylinder misfires and the unburned gasoline is dumped into the exhaust manifold where it is ignited by the hot exhaust from a cylinder that did fire
First, vehicle computers can NOT tell when a sensor is bad, in fact if you get a code and read the definition for that code and it mentions a sensor, then that sensor is GOOD or computer wouldn't know there is a problem
i.e. O2 sensor Lean Bank 1
This means O2 sensor IS WORKING, or computer wouldn't know Bank 1 was Lean
So "don't shoot the messenger"
Even though it is harder to do than throwing easy to get at parts at a rough running engine, compression test should always be first thing you do
Compression is black and white, can't be intermittent, it is either good or it isn't
So once test is done you know if it's the problem, so don't waste time and money on non-fixes
Or you can move on to spark or fuel issues
Remove all spark plugs when doing a compression test, you need fast crank speed
Cold engine is best, you can do warm engine test if cold test shows issues
3.0l Vulcan engine used 9.3:1 compression ratio so new engine should run 165-170psi
More miles 155-165psi
After testing all 6 cylinders and WRITING DOWN the results, there shouldn't be more than 16psi difference between highest and lowest, 10%
If a cylinder is low then retest to confirm
Then add a teaspoon of oil to that cylinder, use a straw in a bottle of oil to pull out oil then release it into the spark plug hole
Retest "wet"
Compression will always go up on a "wet" test, how much of a change can tell you if its Rings or valves that are leaking pressure
If you have two adjacent cylinders showing lower compression then there could be a head gasket leak between the two.
Put spark plug back in one of the cylinders then test other cylinder's compression
Then remove spark plug and test again, there should be NO change, one cylinder can't effect another unless there is a breach in gasket between them
You could just have a vacuum leak, that causes O2 codes and rough idles
After engine is warmed up and idling, about 800rpm
Unplug the IAC Valves two wire connector
IAC Valve will close and RPM should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leaks
If idle stays high then there is a leak
Coil pack wiring on Ford V6 is odd
One side is 1 2 3, the other side is 5 6 4, NOT 4 5 6
1 and 5
2 and 6
3 and 4
These are Match pairs and share the same coil in the coil pack
You also have an EGR system that opens an EGR valve to allow exhaust gases to enter the intake when accelerating, this cools the cylinders to prevent a spike in NOx gas, toxic gas
If EGR valve is opening to soon or leaking then engine will lack power, and would run rough
EGR Valve is opened by Vacuum hose attached to it, there should be NO vacuum at this hose when idling, only during acceleration
Pull off that hose when idling and see if engine smooths out, and that the hose has no vacuum present
Backfires are usually caused when a cylinder misfires and the unburned gasoline is dumped into the exhaust manifold where it is ignited by the hot exhaust from a cylinder that did fire
Last edited by RonD; 06-21-2017 at 10:30 AM.
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