What are the causes of the P0401 EGR insufficient flow code? I searched the forum and could only find 1. This being the DPFE sensor. The sensor has been replaced and I still have the code. Where else should I look?

 

Well maybe a vacuum leak in the EGR's control plumbing, a faulty seal, or gasket, if the engine is using oil, maybe a carboned up up EGR valve thats in need of cleaning, if the EGR valve is realy rusted up & in bad shape, maybe it's faulty, are a few things that come to mind, seeing as how you've already replaced the often faulty DPFE sensor.

Would probably be helpful in making a better guess, if we knew a little more about the rides history, like which engine, how many miles on it, it's condition, where you are on past & present scheduled maintenance items, repair history & events preceeding this trouble code, & are their ANY other codes, if so post them all.

 

Thanks pawpaw,
The engine does not use any oil, however it does leak a little. By little I mean by the time its changed at 3000 to 3500 miles its down maybe a 1/2 a pint. The leak is from the somewhere in the very front of the engine. I have had it on a rack to see if it can be located, but since the leak is sooo small it appears to be elusive.

The problem started about a month ago and was intermittent. The cel would come on and go off. By this I mean it might come on when you turn the key to start it, after you turn it off, it might not come back on for several days. Before I changed the DPFE I had the code run. The only code that showed was P0401, egr flow insufficient. Since this was the easiest and most likely problem I replaced the DPFE. I had the codes run again before I changed the sensor to make sure nothing else was there.

Before I changed the DPFE the engine "bucked" when pressure was applied to the accelerator. I have ridden green horses that didn't buck this bad. If I let off the accelerator the bucking would stop. It also stopped if I floored it or going less than 40. It doesn't start bucking until the temp Gage starts to rise when started cold. The bucking is still occurring but maybe slightly better if any, and under the same conditions

I have avoided taking the egr off as its cold and this is my only vehicle. If its not something I can do in one day, it will have to wait until my next day off(I work Sunday thru Wednesday but Thursdays are out because of moms cancer treatments). I know the egr has never been removed so its going to be a real bear to remove. The oil has been changed regularly and there is no rust in the engine compartment. Internal engine is clean and has had no problems. There is a small exhaust leak on the passenger side. I live in Northeast Arkansas and no salt is used on the roads as we very rarely have icy conditions. Both O2 sensors have been changed within the last year as I had a previous code that the right bank was faulty. Changed them both out. 2 years ago the abs sensor on the rear end was changed out as it was faulty. I really don't want to chalk this up to paid off syndrome but I did just pay it off. The person whom I bought it from took excellent care of it had kept all records of scheduled maintenance and repairs. Upper and lower ball joints on the passenger side have also been changed.

Info in engine:
99 Ranger
3.0 FFV (have never run E85)
123K miles

Parts changed:
Spark Plugs (Autolite platinum)
plug wires
DPFE
abs sensor(rear end)
O2 sensors (L&R banks)
Upper and Lower ball joints (passenger side)

 

OK, good feedback.

Sounds like the truck has had a good looking after from the previous owner & you.

Seeing as how the vehicle has been looked after & engine doesn't seem to be consuming oil internally, & the EGR valve isn't eaten up with rust, I doubt the EGR valve is all cloged up with carbon, or falling apart, so I'd matbe set aside, but not forget, that thought, for now.

But maybe look for loose, cracked, poorly fitting EGR system vacuum lines, rubber hoses, fitings, fastners, gaskets & seals.
There is a EGR valve feedback orface, located under the EGR valves mounting position, thats often forgotten about & it's prone to clog up from carbon and cause mischief, but the valve must be removed to look in there for inspection & cleaning. There are threads on the subject.

On the EGR code, has the CEL light come back on, since you replaced the DPFE????
Did replacing the DPFE affect the bucking any????

I'm wondering if maybe you have two separate problems here.

BTW is this a auto or staight drive tranny????

The "bucking" problem under load sorta suggests to me it may be related to worn plugs or wires. seeng as you didn't list them as having been replaced & they would normally be on the 100K miles "test/inspect/replace" list.

The temp & speed clue's are good one's, but I don't know how to fit the temp one in right now.
Maybe it has to do with something in the system going from open to closed loop operation when warming up.
So perhaps that temp clue will trigger one of the other guys reading that & they'll chime in here with some ideas on fitting that piece of the puzzle into your troubleshoot.

Just some more thoughts for pondering!!!!

 

Pawpaw,
Thanks for the quick reply.
The plugs and plug wires have been changed. They were nice and clean but it was time they were replaced. The truck is automatic transmission.

The bucking did not stop and is only slightly if any better. The cel is still on. I disconnected the battery for an hour to reset the code. The bucking problem is under slight load. Under heavy load(floored into passing gear) it stops and returns when the gears shift out of passing gear.

I will go out and inspect everything I can see and check for anything that might not look right or worn. Thanks for the help so far.

 

OK, just got back in and could not find anything that looked wrong. I even removed the heat shield wrapping around the egr tubing to see if maybe a crack or something was there. The tubing looks as good as new and I replaced the shielding. I pulled off the DPFE tubing and looked inside. From what I could see, they looked good and were not clogged or coated with gunk. I removed them from the other end so I could blow through them. Nothing came out but a small amount of dust. When I tapped them only a small amount of carbon dust showed. They looked normal so I put them back on. I checked all the vacuum lines I could find and they looked good as well. There was no signs of rubbing or anything that could cause a vacuum leak. I pulled the vac line off the top of the egr valve and looked at the little stem it attached to. This too was clean. I am at a loss as to whats wrong.

 

Do this.. start the engine. Remove the vacuum hose off of the EGR valve. Find a vacuum hose that has vacuum all the time and that will stretch to the EGR valve (or add in a length of vacuum hose to make it reach) and put it on the EGR valve. (OR if you have a hand held mechanical vacuum pump you can use it instead). Once vacuum is applied to the EGR valve, the engine should start bucking and missing and will probably die. The is what is supposed to happen.

If this occurs for you, then reconnect everything and maybe try another DPFE... just because it's new doesn't necessarily mean it's not bad. Also make sure it's the correct one for the vehicle... I HIGHLY recommend a Motorcraft part, as the design has been updated (if the new one you installed has an aluminum housing, then it is still the old design, as the new design has a plastic housing) and aftermarket brands may still be using the old one.

If when you apply vacuum there is very little or no change in idle, then you have a restriction in the EGR ports, or an EGR valve stuck closed. You'll need to remove the valve and check further.

Good luck.

 

Thanks MazdaRangerGuyInSTL,
Can you suggest which vac line to use?

 

OK, I did the vacuum thing. The rpm's dropped but it did not start bucking, missing, or die. Dirty EGR? The DPFE has a plastic housing.

How long does it take to remove and clean the egr? and can this wait until I have a day off(next Thursday or Friday)?

 

Ok good inspection & feedback oops.

I think I now understand what the temp clue was telling us.

When the engine in a Ford is cold, there is no EGR function. Also no EGR at WOT & at idle, so the clues you gave about temperature & WOT operation, fit.

As the engine warms enough to go into closed loop operation, the EGR comes online.

So knowing this & the fact you've replaced the plugs & wires, I think we can forget the bad plugs & wires idea I had & get back to looking at a EGR system operational problem, for which we have a trouble code..

MazdaRangerGuy has given you some ideas on how to check the EGR valves operation. So I'd do that.

It seems to me it's likely working ok, if it closes at WOT, as it should & is closed at idle & cold temp operation, as it should be & apparantely is, as it doesn't buck, or run rough, under those conditions, so it seems to me, the VSV & DPFE are likely working & properly controlling the EGR valve during those times, which suggests to me they may be ok too, just that somethng is triggering them to misbehave & operate the EGR valve at the wrong time, or in the wrong way, question is what??????

We know the computer controls the EGR valve through signals it sends to the EVR & DPFE & they seem to be working ok at certain times, like when the engine is cold, or at idle, or at WOT, when your not supposed to have any EGR feedback, so seems to me that leaves us looking at some other sensors the computer uses, to help it determine WHEN to begin to wake up the EGR valve & begin to control it.

To decide when to begin controlling the EGR valve & set the duty cycle for it's operation, the computer uses inputs from it's ECT (Engine Coolant Temp) sensor, TPS (Throttle Position Sensor), MAF (Mass Air Flow) sensor, TCC (Transmission Control Computer) system & engine RPM.

So, it seems to me the ECT is probably working ok. as it doesn't act up when the engine is cold.

The TPS MAY be ok, as it seems to be funcioning ok at WOT, when the jerking stops, but maybe NOT be ok at mid throttle, when your going along at 40 mph & it jerks when you begin to open the throttle, so we'll put the TPS midrange operation on the suspect list for now.

MAF sensor, well your not complaining about other driveability problems like engine ping, ect & we don't have a trouble code for the MAF, BUT you do complain about bucking when opening the throttle, so if the MAF is dirty & it's signal is corrupt, maybe it goes on the suspect list for now.

TCC, well again your not complaining about shift problems & you don't have any trouble codes for the tranny, so maybe it gets a pass.

Engine RPM, well your not complaining about the Tach misbehaving, so I suppose we can assume the signal for RPM the computer is getting isn't corrupt.

SO, that sort of leaves us looking at the TPS & wondeing if it's mid range resistance readings are corrupt & not smooth.

Seeing as how your complaining about it acting up at about 40 mph, when you give it throttle, maybe the bucking problem is with a acting out TPS????

You can check it out with a good analog multimeter, to see if it's resistance changes smoothly, as you slowly open the throttle. A noisey jittery resistance reading from the TPS is a common problem with throttle response complaints.

Could this be the cause of your P0401 code too, I don't know, maybe, but that code is for too LITTLE EGR & your not complaining about engine ping, which it seems to me you should hear, if you didn't have enough EGR!!!!! Too little EGR doesn't cause a rough engine.

Or maybe you do have some ping & just haven't menioned it.

Or maybe we have a typo error & the code should be P0402, which is for EXCESSIVE EGR & that WILL cause a rough runnig engine!!!!

So can you confirm your EGR code really is P0401, insufficient EGR????? Or is it P0402 excessive EGR????

MAF sensor, well if it's dirty, you could have some throttle response problems, that could cause stumble but it wouldn't likely be temp sensitive.
I don't know enough detail on just how the MAF figures in on the EGR's operation.

So it seems to me maybe the TPS & MAF belong on your suspect list for now.

Anyway just some more thoughts for pondering.
Sorry this post is so long,but I had a zillion thoughts & just had to get em all written down before they left me!!!!

Keep us posted on your findings.

 

Pawpaw,
I love long posts, especially when it gives me more avenues to check.

The code is P0401

No pinging

Idle is a bit rougher than when new but not anywhere near bad

I am really beginning to think this is "Paid Off" syndrome. Ya take care of it while ya owe, and it pays ya back when its paid off .

Thanks for all your help.

 

I can't work on the truck until Thursday but before I do I will have the code run again at 2 separate places. Just to make sure and give me peace of mind. Maybe Auto Zones reader is reading wrong or something.. Long shot but who knows.

 

Not a bad idea to have the code number checked again imo.
If it's a P0401, maybe while your there make loan of a mechanical vacuum pump tester, from their loan-a-tool program, to retest the EGR valve, to see if it's diaphragm is sound & holds a vacuum.

If it does hold a vacuum ok, then it's likely dirty & stuck like MazdaRangerGuy said.

Just brainstorming here, but I suppose you could also try disconnecting the EGR valves vacuum control line & plug it, to effectively disable the EGR valve temporarily.

Then drive the vehicle & see if you still have the bucking problem.

That should answer the question about the EGR code & if the EGR is causing the bucking problem.

The reason I suggest this is, I think maybe you could have more than a EGR problem, as a P0401, (too little EGR), shouldn't cause a bucking engine, like a P0402 (too much EGR) would.

So I'm thinking maybe you also have another unrelated problem thats causing the bucking.

Like a dirty MAF sensor, or a TPS with a faulty wiper on it's variable resistor, such that the computer doesn't realize the throttle has moved & the A/F mixture goes lean for an instant.

Or maybe something else that causes the air fuel mixture to go lean enough to cause a stumble on a warm engine, at throttle up, but not bad enough to set another code, like a misfire code, ect.

The reason this could be a temp sensitive condition is, when the engine is cold & in open loop, the A/F mix is richer & less sensitive, to feedback.
Then when the engine warms enough to go to closed loop, the A/F mixture goes leaner & the system is more sensitive to feedback & more prone to stumble if things aren't just right.

If you don't own a multimeter maybe you could also make loan of one of those to test the TPS.

Just some more brain storming ideas for consideration.

 

Actually, low flow COULD cause a bucking/jerking. The flow of the recirculated exhaust that enters the combustion chambers is not measured by the Mass Air Flow sensor, therefore the computer has to calculate the amount of air flow based on commanded EGR status.... so if the computer THINKS the valve is open, it calculates a certain amount of air flow and adds it to what the MAF measures. When the flow is low or non-existent, then the fuel/air mixture ratio is thrown off and driveability problems can result.

I'm banking on carbon build-up in the EGR passages. First, remove the DPFE hoses, start the vehicle and make sure you have good exhaust flow going to the DPFE sensor. The disconnect the exhaust tube going to the EGR valve, then start up the vehicle and make sure you have good exhaust flow going to the valve. If no problems were found there remove the EGR valve and thoroughly inspect the ports in the valve itself, and in the engine for carbon buildup.

I've had luck cleaning these with wire brushes, drill bits (be careful not to drill holes in the intake itself), lots of intake cleaner spray, and sometimes an occasional wire coat-hanger will do the trick. In extreme cases the intake may need to be remove, but not usually necessary.

Good luck and let us know what you find.

 

Interesting angle on the low EGR flow MazdaRangerGuy, but wouldn't the A/F ratio then be rich, rather than lean as it would be with too much EGR flow???? I mean if the computer has looked at the MAF for incoming air flow volume, then calculated what the EGR duty cycle should be, but the EGR valve doesn't deliver, then seems to me the A/F ratio would then go rich????

How does the computer determine the EGR flow is low???? If we knew that, therein may lye a good clue to the EGR code he's getting!!!