Another post on pinging, with a twist...

[94ranger3-0]

Hi all, I have a question about pinging during acceleration. I have looked through the forums for answers and can't really find what I need. So questions: (I apologize if this isn't in the correct forum, it kinda could go in trans or electrical too.)

My truck pings during acceleration, and the trans feels like a 5 speed, but the twist is that when it is 30 degrees F outside or cooler, the engine runs quietly and the trans shifts like a dream. The engine was rebuilt 12 months ago and the trans was rebuilt about 3 months ago. SO my question is... why do these seem to go had in hand and disappear at the same time? I found this post:

http://www.therangerstation.com/forums/showthread.php?t=115286

But, it seems these problems have something in common, which i guess would be electrical (the pcm). Would air flow or fuel affect trans shifts? And why would outside temp affect it?

The engine timing is set @ 5 degrees BTDC with the SPOUT connector pulled. It is a 3.0 with an A4LD Transmission.

 

[RonD]

Pinging is caused for the most part by cylinder temperature, bad timing can also cause it but that is easily checked.
Air/fuel mix self ignites prior to spark because of cylinder temperature.

High compression engines generate more heat during compression.
The higher the octane of the fuel the higher temp it can take before it self ignites, so high performance engines use high octane fuel, to prevent pinging not because it has more power.
Running a higher octane can help reduce pinging on a lower compression engine, the cause of the pinging wouldn't be octane related, there would be an underlying cause, higher octane fuel just reduces the symptom.

Anytime the engine is under load, i.e. accelerating or going uphill, the cylinder temp will go up, that is normal.
The air/fuel mix helps cool the cylinder, so running lean can cause pinging because there is less cooling from the fuel.
Colder outside air can reduce pinging, for the obvious reason, because it cools the cylinder more than warmer air.
The EGR system cools the cylinder, it is to help reduce emissions, but it is now an important part of cooling the cylinders to prevent pinging, I know, hot gas lower temp???, lol, but it does reduce cylinder temp.
The pinging itself also raises cylinder temperature, so once it starts it can increase rapidly, and can cause melted plugs, valves and even pistons, if allowed to continue.

An air leak in the system would cause a lean mixture and change vacuum pressure for shifting.
EGR operation is also vacuum base, lower than normal EGR flow under load would raise cylinder temp and cause pinging.

Also check for PCM updates for your year and engine, Ford may have goofed on mixture and timing changes and have since updated the firmware.

The throttle position sensor(TPS) also plays a part in fuel mixture and maybe transmission shifting

When you first start up the truck on a warm day, and accelerate, do you still have the pinging or as much pinging?
The reason I ask is because before the engine warms up the PCM runs the engine rich, like a "choke" setting on a carburetor engine, if there is no pinging then engine may be running too lean when warmed up.

 

[94ranger3-0]

To answer the last question first, yes, on a warm day the pinging is there immediately. Didn't find anything online about a PCM update, but I will contact a local Ford service department tomorrow morning.

I tried something yesterday.... I checked the kick-down cable and found that the gas pedal wasn't engaging it at all, so I adjusted it as the Haynes manual instructed. And to sum it up, I re-adjusted it today back to the way it was. When it was adjusted properly the trans didn't want to shift into third, then the lockup was kicking in hard about halfway through third gear, then when it finally got into OD it wouldn't downshift unless i floored it, (then it slammed hard down into third), or got below 40 mph and pushed the pedal.

In the Haynes manual there are guides and specs on checking components of both the EGR and electrical system, and i can always use WD 40 or carb. cleaner to search for vacuum leaks.

I am also going to borrow a timing light and set the timing back to stock.

So I guess right I need to check for vacuum leaks and maybe the TPS?


Thanks for your response

 

[RonD]

If it pings with engine cold then yes I would adjust the timing.

I believe the '94 3.0 used a DPFE(differential pressure feedback) for the EGR system.
I would check those vacuum hoses carefully, they could give you a double wammy with air leak and improper EGR flow.

There are way to test both the DPFE(voltmeter) and EGR valve while truck is running.
Just Google Ford DPFE EGR testing

 

[94ranger3-0]

Hi again, I'm borrowing a timing light later today so I will adjust the timing tomorrow (hopefully). DPFE voltage signal is good at KOEO. I don't have a vacuum pump to check the other components, (it is on my to do list though.)

Also, last night on the drive home, when I pushed the gas I could hear the flap for the a/c-heat system that controls whether external air gets in the cabin, open just a little and whistle as air flowed through, and as soon as I got off the gas completely, regardless of my speed, it closed back.

I did bring the engine up to operating temp and removed the vacuum line to the EGR valve and there was no change to the motor idle, and then I repeated it with the motor revved with the same result...

Also, I couldn't locate any vacuum leaks in the system.

 

[94ranger3-0]

update: voltage on SIG is .56 volts. This site says .45 - .55. Is that close enough or is that bad?

http://rockledge.home.comcast.net/~rockledge/RangerPictureGallery/DPFE-Voltage-Test.html

 

[RonD]

Vacuum in the intake manifold is generated by the position of the throttle plate.
When it is closed(at idle or at speed) the vacuum is the highest.
The more the throttle plate opens the less vacuum is in the intake.
This is the opposite of what most people think, if they even care, lol.

So with foot on the gas the vacuum is less so "blend door" opening slightly could mean a vacuum leak somewhere, i.e. the vacuum at WOT is not enough to hold "door" in position, not sure how the "door" works on your model so just guessing.

You can use your mouth/lungs to generate a vacuum to test DPFE or EGR, a vacuum pump and gauge is nice to have but not need for most DIY testing, only for exact pressure testing.
.56 should be fine but I would retest and apply a vacuum.

I would also test the EGR valve again with engine idling, put a vacuum hose on it and suck on the hose, engine should start running rough or die as EGR valve opens.

 

[94ranger3-0]

Hi again, sorry about the lengthy response time, I just got a chance to work on the truck again. I ran the truck to operating temp. then killed the engine to run checks. For what I've found, the EGR and the TPS are both functioning correctly. This time voltage from the PCM to the DPFE and the TPS reads 5.1. So that eliminates the PCM too. Now further observation... the (as you called it) blend door opens as soon as I turn the truck off and it didn't use to. So I agree that there is a vacuum leak, I cant find it though. I have the timing light but haven't had time to adjust the timing yet.

I'm wondering if the vacuum leak is on the line that runs through the firewall. but if I disconnect the hose and cap it, I can't think of a way to check if I keep vacuum in the rest of the system. Any Ideas?

 

[2002rangerv6xlt]

I'm not sure which model you have, but the 90 degree curved rubber hose plumbing my PCV to my intake plenum was cracked at around 130,000 mi on my 2002 3.0L V6. You might want to check that location for vacuum leaks. It was close to the firewall on my V6.

Regarding your pinging, I would suggest that you check your spark plug gaps. I've noticed that a closer gap than specified can cause some pinging.