'07 Ranger 3.0L stumble on WOT, backfire, random misfire

Derf_the_Mule · Dec 13, 2014

I checked the O2 data per the article suggested by TxGasRacer. The O2 sensors respond just as they should when I spray Gumout into the intake.

I discovered that previously the 2nd bank O2 sensors were not working because they were not warmed up yet. All the O2 sensors appear to be working fine.

Using this method (carb cleaner sends O2 sensors rich) I sprayed Gumout carb cleaner around the manifold and found a very small vacuum leak on my IAC valve. Will be repairing that now and rechecking. This is a very small leak on the manifold/ plenum side of the IAC. It is hard to believe it could cause this much problem.

Derf_the_Mule · Dec 13, 2014

Things I've noticed on the scanner watching values graphed while running:

The TPS tends to read 0-0.4% at closed throttle. Does this indicate a bad TPS?
Short term fuel trim jumps to very positive when I snap to WOT.
MAF reading shows the stumble on snap to WOT as a down spike on the curve.
O2 reading show a similar dip on snap to WOT.
The 2nd bank O2 sensors responded in a dampened fashion from the carb cleaner.

If I haven't mentioned before the truck has 81,900 miles on it.

I put HondaBond HT in the IAC gasket (rubber figure 8 type) as a temp fix. No change in random misfire or stumble on snap to WOT. I haven't been able to get it to backfire this morning.

Not sure what else to check or how to use the short term trim and MAF reading to determine bad sensors. As far as I can tells right now everything is working.

When I did the last compression test after getting the engine to full operating temp (driving for 20+ min) I noticed some white smoke or vapor coming from cyl 2+3 out through the tester when I relieved the pressure.

Derf_the_Mule · Dec 13, 2014

I finally pulled off the right side O2 sensor to check backpressure. The needle didn't move on my 100 psi gauge. If it was more than 5 psi it would have shown something. I am pretty sure it is not plugged cats. I couldn't get the left O2 sensor off. Freezing it didn't help even.

I removed the MAF sensor unit from the housing and cleaned it again with CRC MAF cleaner. I took the neg bat terminal off to reset the tables. There was no change that I could tell. I need to drive it some to be certain.

I did notice that when I snap to WOT that the O2 sensors go rich for several seconds after. I also was able to get my hand under the plenum and pull the connector off the #4 fuel injector. I pulled the connectors off all the FI's one at a time to see if the rough idle goes away with any particular injector. The idle becomes consistently rough with any one cylinder misfiring, but I could not point to one that didn't have the roughness of the random misfire in it. I am pretty sure it is not the injectors.

I did a test a few days ago to see if any of the injectors were leaking. I turn on the fuel pump and let it run for more than 5 min. I disconnected the connector from the coil pack to prevent spark. I then cranked the engine over several revolutions to dump any leaked fuel into the cylinders. I then pulled all the plugs one at a time to look and smell for gas. All were dry with no smell of gas.

I cleaned up a ground between the engine block and body at the body. Nothing major, but it had some resistance when I continuity checked it. Made no difference.

Derf_the_Mule · Dec 14, 2014

Is there anyone out the that works for or has worked for a Ford dealer? I need to know if I go into the dealership with the KOEO fuel pressure out of spec that they will clearly recommend having the sending unit replaced.

My mechanical repair coverage through my credit union will cover the fuel pump, but I have to pay the diagnosis fee upfront. I don't have $100 to waste on an "don't have a clue" response. I also don't want to waste a morning at the local dealer for an unsure response. I have not been able to get an intelligent response from a "service adviser" over the phone.

hopster · Dec 15, 2014

Unfortunately without physically looking at the truck I don't think anybody can offer you any real solid yes or no answers. but if it were to come to me I would definitely check the synchro with the ford tool and do fuel pressure and ethanol tests depending on the pid data info. also have you checked for slop in the timing chain.

Derf_the_Mule · Dec 15, 2014

I am looking locally to find someone that can do a fuel test.

Is there a way to check the timing chain for slop without removing the timing chain cover and partially disassembling the engine? Last time I did that was on a late 70's Ford 302 V8 about 20 years ago. This engine is smaller, but has a lot more stuff in the way.

Derf_the_Mule · Dec 16, 2014

I was able to drive some today after resetting the PCM yesterday. I don't know if I drove enough to reset the tables in the PCM.

I did notice it is harder to get it to stumble on acceleration while driving. It did stumble on snap to WOT when I got home. I didn't do anything today as I was dealing with the family car (2001 Honda Odyssey) getting its tranny #2 rebuilt.

I got my hands on a 2007 Powertrain Control/ Emissions Diagnostic Workshop Manual. I will be following the diagnostic directions in it to see what I can come up with. It will take me awhile and my code reader does not appear to read all the PID's I may need it to read.

Derf_the_Mule · Dec 17, 2014

hopster said:
I didn't see any mention or a fuel quality test. if there is excessive ethanol or water in the fuel there can be some pretty goofy symptoms. also I would verify the cam synchronizer alignment. it's easy to get that wrong. also you have a mechanical returnless style fuel system on that truck. any pressure concerns should be rectified by replacing the pump assembly.

Is the low KOEO pressure (10-30 psi on startup, 60 psi pump on to max then off) enough to justify replacing the fuel pump assembly? I followed the PC/ED Manual method for testing the fuel pump (accelerate from stop to 55mph 3x, if pressure above 35 psi not the problem) and that says no. However, I have learned the hard way to trust actual experience over a book written for general use and many engine configs. The low KOEO pressure is the only symptom I have to point to.

Derf_the_Mule · Dec 17, 2014

I haven't found a fuel quality test locally yet. I will have some time tomorrow to do more searching.

I drove more today and tested a few more components. I checked the resistance of the camshaft position sensor and AC voltage (connector off) at 2500 rpm. Spec says 250-1000 ohm, and >0.25 VAC respectively. Passed both tests. I am pretty sure I can rule out the CMP as a problem.

Have not checked the wiring harness per PC/ED. Have not had the gumption to go that route yet. I tried to check power and ground to the fuel pump, but the connector is near the body such that it cannot be removed without lowering the gas tank (what jerk missed that one). I don't like using wire piercing probes either.

Noticed while backing up it runs very rough at idle, but didn't throw any DTC's. It has done this to me several times (runs like crap in reverse on level and un-level ground). Overall, it is running better since I gapped the plugs to 0.043", but the random misfire is still there and the hesitation on snap to WOT. I recorded the PIDs when testing 0-55 WOT acceleration. If it will help anyone let me know and I will post them. Power feels low in 1st and second gear.

I noticed the PID for TPS% only goes to 74% at WOT. Does that mean anything? I have purchased a new TPS anyway and will replace it when it gets here next week. I had a problem with my '98 Ranger 4.0L TPS showing good but driving terrible (don't get carb cleaner or throttle body cleaner anywhere near a TPS). We'll see if this is the same issue.

hassanov · Dec 18, 2014

Thanks for suggestions and tips

Derf_the_Mule · Dec 18, 2014

I was able to do some research on fuel testing today. After reading several websites I thought I would have to order and wait for a test kit ranging from $9-$40. I discovered all I needed to test ethanol content was a graduated cylinder. I don't have a graduated cylinder, but I do have several syringes for dosing liquid medication.

Method: I used a 10 mL syringe (pharmacies may give them to you for giving childrens meds). I filled it almost full of water then squirted it out until the 2 mL line. I then pulled in as much gas as I could get in and squirted it out (use an appropriate container) until it hit the 10 mL mark. That is 2 mL water 8 mL gas. Shake it and let it sit for a few minutes with the tip up. Read the line between the 2 liquids (should go up) at 7.2 mL. 1 - (7.2/8)= 10% ethanol/water. FYI the smaller the test sample the larger your chance for error.

Resolution of excess ethanol concern. I do not have excess ethanol in my gas. I don't have access to expensive gas chromatagraph or any other lab equipment. So fuel contamination with other things is still possible, however unlikely.

I ran the battery dead last night when I left the ignition on. I am charging the battery right now. I did notice that my fuel pump pressure at 11.9V (tested at 12.3 V with another battery, same results) would only go to 66 psi. That is 1 psi above spec and the pressure now drops quickly to 55 psi in about 1 minute then drops to 45 psi in 15 minutes. This tells me the fuel pump is marginal and the pressure regulator (on the fuel pump/ sending unit assembly in the gas tank) is bad and getting worse.

This is something I have to take to a dealer or mechanic because it is covered by the mechanical insurance plan I bought from my credit union. I will update when repaired and update on the TPS replacement as well.

Derf_the_Mule · Dec 18, 2014

I need to clarify what the test I described above tells. It does not tell the amount of ethanol in the gas. It tells the amount of miscible liquid in the gas. The miscible liquid that separates when more water is added can be a combination of alcohols (ethanol, methanol, isopropyl), water, and any other detergent that can dissolve in water or petroleum. The idea is to add more water and overwhelm the non-fuel stuff so the fuel will separate out.

It is assumed that it is ethanol because that is added to fuel. It is likely ethanol because of the EPA ethanol fuel mandate and possibly other alcohols and/or detergents that will dissolve in water.

Since, I don't have access to expensive lab equipment and I don't have budget to pay a lab this test is sufficient to tell me I have less than 10±1.5% ethanol/ water mixed into my fuel. Since the gas station I use is busy I am assuming the fuel is not contaminated enough to cause the problems I've been having.

FYI: Seafoam has Isopropyl alcohol in it. Iso-Heet is mostly (95-99%) isopropyl alcohol and Heet is methanol. Use with judgement and skill.

Derf_the_Mule · Dec 18, 2014

For any fuel pump or mechanical returnless fuel system expert out there (at the moment I would settle for someone been there done that), when I turned on the fuel pump with my relay bypass switch it took 5 sec or so for the fuel to max out at 66 psi. I also sounded like the fuel pump was struggling. Ford spec for this truck is 65-75 psi. My KOEO fuel pressure hovers around 10-30 psi for the 1 sec on burst when the ignition is first switched on. It would take me 5-6 switching cycles to get near the spec KOEO pressure.

When I first put the bypass switch on and ran the pump it would go to 68 psin in about 2 sec. When I shut it off it would immediately got to 58 psi then drop slowly to 0 over an hour or so. I can clearly see it is getting worse.

Back to my question... Is it screaming CHANGE ME yet or am I being overly cautious about the problem?

Derf_the_Mule · Dec 18, 2014

I just got back from driving with the fuel pressure gauge on. It revealed some interesting correlations.

I accelerated from 0-55 mph at WOT 3 times and watched the fuel pressure gauge. The running pressure was 68-70 psi. There was a consistent slight dip in pressure when I snapped the throttle open. This is new and didn't happen last time I tested it.

At idle when I got home just before every misfire rough stumble the needle on the gauge dips down 1± psi. The needle shakes in direct correlation with the hesitation, stumble, and rough running.

I can say with pretty good certainty that if it is the injectors (which were just cleaned and flow tested) it is more than one. But, this is telling me something is wrong with the fuel system. Bad regulator, dying pump, clogged fuel line, clogged return line from filter, and/or bad 1 month old filter. Understanding pumps the way I do, I can see that pressure clearly is not the problem. The problem is volume. pressure is meaningless if your pump or regulator does not allow the volume to run the engine. When I hit the pressure relief button on my fuel pressure gauge the pressure drops to 0 psi quickly. Anybody have a spec or test for a fuel volume test for a 2007 returnless fuel system?

Yes, you in the back jumping in your seat go ahead...

Derf_the_Mule · Dec 18, 2014

I now have a clear direction to pursue.

-I need to test the fuel lines for restriction. Any ideas how without an air compressor (I know I need to buy an air compressor)?
-I will replace the fuel filter just to be sure that isn't the problem.
-Drop the fuel tank enough to get to the electrical connector and test power and grounds and allow access to the fuel lines for testing.

The fuel lines are not covered by my mechanical plan so I need to check them and repair them as needed first.

'07 Ranger 3.0L stumble on WOT, backfire, random misfire

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