P0401 EGR troubleshooting (1 Viewer)
- Thread starter Stecz
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Malleus
Far west of Siegen
That got it. Thanks!
Great write up, BTW.
Great write up, BTW.
Malleus
Far west of Siegen
I think this may become my preferred way to clean an intake manifold:
Intake manifold cleaning
Intake manifold cleaning
Malleus
Far west of Siegen
I'm just leery of trying it because if the neighbor's kids see it, I'll never get rid of them...
- Thread starter
- #26
I'm still struggling,
I tried to spray into the 2 ports from the TB to EGR, one definitely not clogged, but the one closer to front of engine is definitely clogged. When I spray solvent, it just spits it out. I also put a mity vac on it and the port is not open. I tried to run a wire down it and it stops at a certain point of time.
Also, I tried to test the vacuum modulator. Should it hold a vacuum on the bottom port? Also I can't blow air through port P. I tried to poke a drill bit through and it has a hard plastic stop.
I think that I need to replace the modulator and remove the TB and clean that port.
I tried to spray into the 2 ports from the TB to EGR, one definitely not clogged, but the one closer to front of engine is definitely clogged. When I spray solvent, it just spits it out. I also put a mity vac on it and the port is not open. I tried to run a wire down it and it stops at a certain point of time.
Also, I tried to test the vacuum modulator. Should it hold a vacuum on the bottom port? Also I can't blow air through port P. I tried to poke a drill bit through and it has a hard plastic stop.
I think that I need to replace the modulator and remove the TB and clean that port.
If you've found a clogged port on the TB then that's good because you've found at least one for sure problem. You definitely do not have to take the TB off to clear that port but you will need to remove the brass elbow to be able to clean it. The TB is drilled part-way for the brass elbows but this larger diameter hole does not continue into the intake passage. A much smaller pinhole is drilled into the bottom of the larger/brass nipple hole and this pinhole does connect to the TB intake passage. So, little carbon chunks can make it through the elbow but can't be sucked into the intake and they get stuck in the bottom of the larger drilling.
You don't want to take the TB off to clear these ports because they could get clogged repeatedly if there is debris in the system. That's what I've experienced though mine stopped getting clogged after a while and I've not needed to clear the TB ports in about a year. My Modulator P port has continued to clog though.
To clear the TB ports you can take a pair of vice grips or pliers and gently grab the elbow near the 90 angle and gently twist it and pull it out of the TB. It's just pressed in and should come out relatively easily. Don't grab it tightly enough to bend the elbow itself. Once the elbow is out you will have more options for cleaning the port and should have more success. I've had luck with a bit of welding wire that's stiff but pretty small. I think that once the elbow is off that clearing the port will be straightforward but I can share more ideas if needed.
You can easily test the vacuum modulator. The test is listed early in this thread:
forum.ih8mud.com
The other thing that I've dealt with in terms of a non functioning vacuum modulator is repeated P port clogging. I've cleared mine at least a dozen times now which means that little carbon chunks are in the system somehow. I took an old modulator apart and the P port has a small diameter constriction which is why it clogs so easily. I just remove the line on the Q port and the P port and then I blow a bit of electronics cleaner into the P port until it soaks a paper towel that I place on the Q port end. I then button her up and run the engine to clear the solvent. This will last weeks to months on my 80 and I typically only have more clogging of the P port after extended interstate speed runs. I've added a filter to the system to see if this resolves the issue moving forward but have to wait a few more months before I'll have confidence that it did.
If you've got a clogged port in the TB you likely have the P port clogged on the VM as well. Once you've cleared them a first time it's easy after that and only takes a few minutes.
Good luck,
You don't want to take the TB off to clear these ports because they could get clogged repeatedly if there is debris in the system. That's what I've experienced though mine stopped getting clogged after a while and I've not needed to clear the TB ports in about a year. My Modulator P port has continued to clog though.
To clear the TB ports you can take a pair of vice grips or pliers and gently grab the elbow near the 90 angle and gently twist it and pull it out of the TB. It's just pressed in and should come out relatively easily. Don't grab it tightly enough to bend the elbow itself. Once the elbow is out you will have more options for cleaning the port and should have more success. I've had luck with a bit of welding wire that's stiff but pretty small. I think that once the elbow is off that clearing the port will be straightforward but I can share more ideas if needed.
You can easily test the vacuum modulator. The test is listed early in this thread:
EGR Modulator Testing ?? HELP
So I have been fighting the PO401 code :bang:. I got a shipment of parts in from CDan and replaced EGR valve, small hoses, temp sensor and the upper intake gaskets. I got her up and running yesterday afternoon. After warming her up I went for a 10 mile drive to see how everything is working...
forum.ih8mud.com
A failed vacuum modulator will show contamination of the filter. You can just pop the top cap off and see if it's really dirty. Add that to running through the tests above to evaluate if it's bad. The other thing that I've dealt with in terms of a non functioning vacuum modulator is repeated P port clogging. I've cleared mine at least a dozen times now which means that little carbon chunks are in the system somehow. I took an old modulator apart and the P port has a small diameter constriction which is why it clogs so easily. I just remove the line on the Q port and the P port and then I blow a bit of electronics cleaner into the P port until it soaks a paper towel that I place on the Q port end. I then button her up and run the engine to clear the solvent. This will last weeks to months on my 80 and I typically only have more clogging of the P port after extended interstate speed runs. I've added a filter to the system to see if this resolves the issue moving forward but have to wait a few more months before I'll have confidence that it did.
If you've got a clogged port in the TB you likely have the P port clogged on the VM as well. Once you've cleared them a first time it's easy after that and only takes a few minutes.
Good luck,
- Thread starter
- #28
I tried to pull the elbow out of the TB, but couldn't get it out. I'm going to try harder today.
I'll also pull the modulator and take it apart to inspect.
thanks for the confidence builder, I was nervous about pulling the elbow out.
I'll also pull the modulator and take it apart to inspect.
thanks for the confidence builder, I was nervous about pulling the elbow out.
- Thread starter
- #29
finally solved the problem... the port on top of the TB was definitely clogged, resolved that. Code still came back, I tried to troubleshoot the vacuum modulator and didn't pass the tests posted above, so I replaced it. Code is gone and it has passed the annual emissions test. Ironically, next year it's emissions exempt.
Thanks for all of the help and hints.
Thanks for all of the help and hints.
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What range of vacuum are you reading here when bypassing the VSV and reading directly after the EGR Valve? I plan to confirm my TB ports are still open and I need to find and do the VM and VSV tests but while trying this, I read a very small amount of vacuum <5 inHg when revving up to 2,500rpm.
I plan to replace the VM because I tested it and it doesn't hold vacuum at the bottom (slow leak). The VSV is new and temporarily relocated near all the connectors to the TB...I'm worried it's too hot there and want to move it again but need to make sure it works. The only part of the system I haven't touched is the EGR temp sensor (except to test that it's getting 5V and it read 10 Ohms on the connector so think it works). It would be really obvious if someone had disabled or bypassed the sensor right? Wondering if I'm missing something.
@jatree
I don't recall the readings or what my guages range even is but I can say that the needle movement was clear and obvious. If it's essential I don't mind doing some tests but if you just want to figure out if the ports are clear I can recommend an easier way to do that:
-Grab a can of brake clean with a tube on the spray nozzle and a paper towel.
-Pull the rubber vac. hose off of the brass elbow for one of the vac. ports on top of the throttle body.
-With the engine running stick the brake clean tube into the brass elbow and give a little squirt. This should impact engine rpm. If it doesn't rev the engine up to 2k rpm or so and try again.
-If no rpm impact then I'd suspect a clogged port. My cleaning technique is to gently pull the elbow using pliers and a twist/pull movement then a bit of welding wire to scrub around and find the small orifice in the TB and push it clear. Keep in mind that the drilling for the elbow is way larger than the small orifice that the vacuum passes through.
-Reinstall the rubber hose on the elbow and test/clear the other port.
Also, if you just want to use your vac guage and not Brake clean comparing one port to the other should give you a sense of vac levels. Run the RPMs up and down when testing each port. One of the ports is before and the other after the TB butterfly as I recall so the vac levels really differ at idle but are closer as the throttle opens as I recall.
I don't recall the readings or what my guages range even is but I can say that the needle movement was clear and obvious. If it's essential I don't mind doing some tests but if you just want to figure out if the ports are clear I can recommend an easier way to do that:
-Grab a can of brake clean with a tube on the spray nozzle and a paper towel.
-Pull the rubber vac. hose off of the brass elbow for one of the vac. ports on top of the throttle body.
-With the engine running stick the brake clean tube into the brass elbow and give a little squirt. This should impact engine rpm. If it doesn't rev the engine up to 2k rpm or so and try again.
-If no rpm impact then I'd suspect a clogged port. My cleaning technique is to gently pull the elbow using pliers and a twist/pull movement then a bit of welding wire to scrub around and find the small orifice in the TB and push it clear. Keep in mind that the drilling for the elbow is way larger than the small orifice that the vacuum passes through.
-Reinstall the rubber hose on the elbow and test/clear the other port.
Also, if you just want to use your vac guage and not Brake clean comparing one port to the other should give you a sense of vac levels. Run the RPMs up and down when testing each port. One of the ports is before and the other after the TB butterfly as I recall so the vac levels really differ at idle but are closer as the throttle opens as I recall.
richardlillard1
SILVER Star
Some might call this cheating, I call it effective.
The funny thing is, a guy was looking at my truck once and said looks like they did the resistor mod. I don't believe he owned or knew 80s well and it confused me because everything looks stock, nothing like the pre-built adapters you can buy for the connector on here. However now I'm second guessing myself and will look at the EGR temp sensor in the morning to make sure it is unmodified. I know for sure the little hoses don't have bb's in them because I've replaced all the ones on top and the two for the VSV below. I forget what the modified temp sensor does, is it just simulating a condition that never calls for the valve to open? Is the exhaust still pushing against the Modulator? I'm sure I can find these answers and more but point taken. I'd like to try a little more before resorting to the workaround!
Thank you but that's ok, the amount isn't important. I just wanted to know if it was a clear increase in vacuum. I'm using a not super high quality HF vacuum pump but still, my needle moved but just barely up to 2-3 inHg so I'm going to try the cleaning method (probably with TB cleaner since I have it) and hope it works. Appreciate the tip about being able to carefully remove the little brass elbows if needed.
