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

[Derf_the_Mule]

The PC/ED Service Manual said to take the connector off the MAF and drive and see if that stops the problem without DTC's. I did that and it made the problem much worse. That rules out the MAF as causing the rough idle, stumble on snap to WOT, and misfire.

The Actron CP9185 scanner I rented from Autozone does not display all the PIDs it reads. It reads 108 PIDs and displays 39. I can't get to the actual data I need to check for problems because this scanner doesn't show it. My multimeter only reads to tenths of volts. According to an article from www.aa1car.com or a website earlier in this thread (don't remember which) the TPS shows part throttle at 0.04V. The TPS measurement shown on the Actron scanner I have shows the TPS varying at 0.0-0.4% at closed throttle. Since I can't read the actual data sent to the PCM by the TPS this presents a problem. I need a voltmeter that reads accurately in the hundredths of volts or a scanner that displays the missing PID data.

Does anyone know if the Innova 3160 scanner displays the TPS voltage and percentage (as well as the direct data from other sensors instead of just interpreted data)??? Or possibly how to get the rest of the PIDs out of the Actron??? So far the manual has been little help.

 

[Derf_the_Mule]

Replaced the TPS with new Motorcraft one. Seemed to be a little change, but after running it for awhile it seems to be getting worse. I haven't been able to get it to backfire for a week now, but the stumble on snap to WOT is there when it is warmed up, and it is running rough. It also started to idle very high after opening the throttle, and stays high until I bump the throttle again. I sprayed water looking for a vacuum leak and could not identify one. This is very frustrating.

Bad IAC? Bad PCM? Bad Diagnoses?

Haven't messed with the fuel tank and filter yet. Will need to get an air compressor first.

 

[Derf_the_Mule]

Replaced the fuel filter, no restriction that I could determine. Flow tested the fuel pump by filling a jar with 8oz mark from the fuel connection to the fuel rail. It put out about 9±oz in 5.24 sec. Comes out to around 0.805 gpm at free flow pressure (0 psi). When I used the fuel pressure gauge relief it took 30 sec to get about 2-3± oz the gauge read 4 psi. Comes out to around 0.047 gpm. The relief on the gauge is very restricted.

Anybody know the fuel flow spec for a '07 Ranger Sport Supercab 3.0L engine?

Anybody know how to test the regulator in the tank?
Can I use an air compressor blowing into the return line somehow?

 

[Spott]

I'm not familiar with your engine, but it seems that you are over-analyzing lots of things. Usually if something is within a few % of spec, it's probably good. Trying to measure voltage to 1/100 of a volt is unimportant, if your meter already tells you that it's between 0.0 - 0.1 V.

The part I would focus on first is the significant compression loss in the #4 cylinder.

 

[Derf_the_Mule]

I'm not familiar with your engine, but it seems that you are over-analyzing lots of things. Usually if something is within a few % of spec, it's probably good. Trying to measure voltage to 1/100 of a volt is unimportant, if your meter already tells you that it's between 0.0 - 0.1 V.

The part I would focus on first is the significant compression loss in the #4 cylinder.

I have a tendency to over-analyze. However, I don't have enough knowledge to understand the results of my compression tests. In areas where I have limited knowledge I must rely on what others divulge and make a judgement call on who/what/ how much to trust. My current set of knowledge comes from my own experience of 20+ years doing automotive maintenance and repair in the back yard, my father's experiences, information gleaned from coworkers and friends with mechanical experience, Chilton's and Haynes manuals (took 20 years to learn how limited they are), limited contact with mechanics I've hire to do jobs I don't have equipment for, my newly acquired Ford service manuals (not easy to follow or exhaustive), and the internet ( I do know that free advice is not always good).

The cold (overnight) tests show Cyl#4 is out of spec, but the hot (driving 45+ for 20+ minutes) shows less than 5% variation. I am assuming the cold tests are invalid, because Ford manual and everywhere else I've read says do it at operating temp.

Did I invalidate my second set of compression tests by having the entire engine at full operating temp?

To summarize a long explanation: I don't understand how the data show a significant compression loss in #4, please spell it out for me. I've only had 1 engine rebuilt for me (that '86 Ranger 4-banger still runs).

 

[Spott]

The compression for all the other cylinders is almost identical, while #4 is a bit low.

If the others had some variation, it wouldn't seem so suspicious, but the numbers on #4 stick out like a sore thumb. There might have been other possible causes, but you've pretty much eliminated those with previously mentioned repairs and replacements.

Whether or not the compression is causing your stumble, it needs addressed, and it's the most obvious problem at the moment.

 

[Derf_the_Mule]

The compression for all the other cylinders is almost identical, while #4 is a bit low.

If the others had some variation, it wouldn't seem so suspicious, but the numbers on #4 stick out like a sore thumb. There might have been other possible causes, but you've pretty much eliminated those with previously mentioned repairs and replacements.

Whether or not the compression is causing your stumble, it needs addressed, and it's the most obvious problem at the moment.

I appreciate your explanation and do share your suspicion. It does seem to be obvious, but it still has lower likelihood to be the problem since the deviation is 5% (Ford says 25%, others range from 10-30%). I read in a forum (maybe here) that a dealership rebuilt a 3.0L head with lower than spec deviation. If I would not have suspected the injectors first (diagnosis I paid a 30+ year mechanic for) I would have paid more attention when I had the valve covers off.

Unfortunately for me tearing the heads off and getting a valve job will be the very last repair because it is the most expensive. I must eliminate the cheaper and easier possibilities first. I just bought a cheap compressor, maybe I can rent leakdown test equipment.

From what you and others have written and what I've already eliminated the problem is either fuel system (malfunctioning regulator and/or pump and/or blocked line), electrical system, PCM, or burned/ sunken valve. I have a small borescope camera that works on my computer. I may be able to get it into the cylinders to view the valves.

I am working on the front brakes and bearings now. It will be Monday before I get to anything else.

 

[Derf_the_Mule]

New development today. I noticed Friday that my idle was really high 2000+ rpm when it shouldn't be. I could bump the throttle and it would go back down. Today, I went for a test drive after LF brake (and bearings) job. It idled at 1800 rpm cold and after I got home driving for 10 minutes it was idling over 3000 rpm and the rev limiter was cutting out injectors. I shut it off and when I restarted it was still idling around 1200. I pulled the connector on the IAC and it nearly died.

Suspects: Bad IAC valve, Bad PCM (no way for me to test), Bad coolant temp sensor?

I am going to check the IAC with the PC/ED manual and see if it is fried. It checked fine last week, but I may just replace it.

 

[Derf_the_Mule]

I just checked pending codes and got a P0511 IAC Control Circuit code. Tested the IAC and the resistance between the leads is 0.6 ohms. The spec in the 2007 PC/ED manual is 6-15 ohms. The IAC valve is fried. I hope this has been my problem all along. I will update after changing the IAC valve. The short seems to be intermittent. I checked 2 more times and got higher and lower readings.

Update 1 hour later:
It idled high between 1500-3000 rpm while I drove to the parts store to get the IAC.

Replaced IAC. It was not the problem. I tested the IAC + connector to ground and got 340 ohms. It is supposed to be over 10K ohms. Looks like I'll be chasing down a shorted wire for awhile. It could still be the PCM though. Anybody know where I can get a good deal on plastic combs to re-wrap the wiring harness?

 

[Derf_the_Mule]

I did some checking last night and some reading in the Wiring diagram. (Very useful book, worth having.) The grey wire with the short provides the KO 12V power to many components which the PCM individually grounds to operate or monitor. (Which severely complicates finding the short.) If you have the wiring diagram I recommend making copies to make notes on when circuits are eliminated. This can help you pinpoint the line with the short so you do not need to cut open all the wiring harness to locate a problem.

The grey with orange stripe wire on the IAC is the ground via PCM which controls the duty cycle of the IAC (how much it is on). This line does not appear to have a short in it. I pulled the "E" plug and tested resistance at E33 (IAC control circuit) and found no shorts to ground or power. I checked the gray wire after disconnecting all 3 plugs from the PCM to ensure the short was not in the PCM itself. I checked resistance at the IAC fuse (43) and shows there as well as in one side of fuse 44 (KO power to coil pack). If I remember correctly is shows on pin 30 of the PCM Power Relay as well. Looks like the short is somewhere on CE612 GY-VT, S123 (splice), S118 (splice), S108 (splice), CBB43 GY, or one of the sensors connected to those.

What I do understand at this point is something is keeping the IAC open too much. The PCM says the IAC control circuit has an error, but the control circuit tests fine and the power circuit shows a short when hot. To complicate things I have rechecked the power circuit (grey wire) and found the short is gone. That means something is shorting only when hot. That points to the O2 sensors heaters which are powered on the same circuit, but is not conclusive.

 

[Derf_the_Mule]

I rechecked the PC/ED manual again because I could not reproduce the problem. When warm the resistance between the grey IAC power and ground is 340 ohms; when cold the resistance is OL. It appears I misreads the test and voltage is supposed to be less than 1V key off. Which it is. The short has disappeared because I worked when not tired.

Good news is the high idle problem seems to be gone somewhat. I had the PCM unplugged all night. The new IAC and reset tables seem to be working OK. When I started it up I got a wooshing noise from inside the intake plenum (IAC maybe?). I could not isolate it and it went away after the engine reached operating temp. I probed around the fuel injectors and intake, but could not determine a location.

The random misfire is still there and the stumble on snap to WOT is there a little. The RPM randomly drops rather slowly when I open the throttle. I am beginning to think the PCM is fried. I cannot access the IAC duty cycle PID with the Actron Scanner. I will try another vacuum leak test with propane when I find the valve.

Potential causes: bad PCM, burned valve #4, intake manifold vacuum leak,?!?!?!?

 

[Derf_the_Mule]

I responded prematurely. The high idle started again as soon as I drove enough to reset the fuel tables. Last night the PCM was ignoring the the TPS completely and outputting high values as though it was only reading the MAF and using that value as the TPS. I know it can do this in case of TPS malfunction, but I just replaced the TPS.

Today the PCM kept the RPM's around 1900-2000 sometimes it would slowly return to ~700 at idle sometimes it would drop instantaneously then nearly stall and go back up. When I got it home it dropped and did stall. I did not notice the TPS % showing open abnormally as before.

I followed the PC/ED manual instruction to diagnose the code, but cannot access the IAC duty cycle PID or TPS output voltage PID with the Actron scanner. Anybody have better luck with the Inovva one?

I am leaning more towards the PCM needing to be flashed or replaced now.

I am not convinced the IAC was a problem before. It was very hot when I took it off. I think the PCM may have overheated it at 100% duty cycle for too long. I tested it this morning and it seemed fine.

It will be Monday before I take it to a shop to diagnose the PCM and/or fuel pump issue. I will update with the resolution. I did find that a leakdown test kit is around $60.

 

[Maggie may]

I had a similar problem with no start and severe detonation, my problem was not under the hood, nor was it my computer. My ignition cylinder was the problem, I was just losing it over the random intermittent problem I could not find. Replacing the crank position senses,complete tune up, scan tool would give me different codes every time I hooked it up, wiring had no issues either. The problem was in the steering column. There was 2 things my key cylinder, and the connecter. Literally mattered how much pressure I put on the key, I could affect whether it started or not. Sometimes the edis would respond and fire the plugs and other times not. After changing ignition cyl. And changing the connectors on the main harness in the column there has been no other troubles. Who knew the key could cause such a nightmare!

 

[Derf_the_Mule]

I had a similar problem with no start and severe detonation, my problem was not under the hood, nor was it my computer... Who knew the key could cause such a nightmare!

I appreciate your posting. This is the kind of thing I have been looking for via forums.

How did you diagnose the keyswitch and connector as the problem? Did you stumble on it while playing with it or is there some sort of test procedure? The PC/ED manual says something to the effect of look at it, play with it, if it looks bad or acts funny replace and re-test.

 

[Maggie may]

The key cylinder was moving a bit in the housing ,which I noticed a difference in what my engine sounded as it cranked over. So the more times I cranked it over I took time to record why stroke it seemed to be on and if it detonated or flooded, whether the key was jiggled while I cranked engine, whether I applied lot/little pressure on key. When I looked over what I wrote it became evident what was going on. My boyfriend was sure it had jumped timing and the more guys I talked to the worse it seemed. They were all wrong and had I not listened my truck would have bee on the road month earlier