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Interesting issue has popped up with my FD that I have been slowly getting back up and running. I've successfully gotten the car back on the road after a 14 year stint in storage and has been running fairly well, idles good, boosts fine (for the most part) other issue, but then this last weekend it would not rev past about 4500 rpm. Took it out for a drive and it was way down on power and almost couldn't drive itself back up a small hill getting it home. The more I pressed the gas the more sluggish it would feel so I had to feather the throttle on/off to get the car moving under load. Once home I popped the hood and tried to rev the car in neutral from under the hood and noticed a really strange issue. The accordion tubing going to the intercooler and then the intercooler to the throttle body were both collapsing under WOT conditions essentially collapsing under the vacuum of the engine. Has anyone ever seen this condition and know what could cause enough vacuum on those hoses to collapse them?
I removed the cat thinking a clogged exhaust and had the same issue, but if I remove one of the hoses from the intercooler I can freely rev the engine and feel the boost pressure from the turbo coming out.
One other thing I noticed is that if I try and go full WOT then the car revs to 4500, hits a wall and slowly falls off rpm, however if I gradually rev the car to about 4500 then quickly pump the throttle pedal I can get past the 4500 and then rev out to full rpm. Gotta say any help would be appreciated, and any insight on what to check.
Things I have read are secondary injectors may not be coming on so I need to dive in there, as well it's possible that I've lost a leading coil pack or trailing?
Things I've done and deleted:
EGR removed
ACV removed
Accelerated warm up removed/bypassed
Air pump removed
All solenoids for associated systems removed, however I have not bypassed wiring and have codes for all those systems I removed. Codes are 16, 25, 28, 30, 31, 32, 33, 38, 39, 42, 43, 54. All associated with what I removed and was curious if these can put the car in limp mode because the car has driven perfectly for over 150 miles.
Aftermarket boost controller installed running simplified sequential setup version 2 so both I and J solenoids are removed. Essentially I am only running solenoids E, F, and H.
I'll be installing a PFC soon, but can limp mode cause the intake hoses to collapse? I wouldn't think so. TIA, more work ahead.
94' FD stock engine.
I would say you are in limp mode with the removal of the egr and the listed items. Did you happen to notice any codes being present before the removal of sensors and parts? Old rubber intercooler hoses can potentially pop off if not secured properly and pinch. If this FD has been sitting in storage for 14 years I would recommend a compression test so you have a general health condition of the engine. Due to the removal of parts I would definitely plug in the power fc and see if the conditions follow. if you notice the hose collapse inspect and replace. Once you install the power FC and follow the learning steps we will be able to see a few things on the sensor diagnostic screen and go from there.
One code can cause limp mode. Trying to run a stock ecu with all those deletions is a no go.
The ecu may cycle through sensor checks and so there may be some delay before going into limp mode.
What is your boost gauge showing when the air hoses collapse?
Very curious what is going on there.
My car had all those deletions, but the harness was left intact. We hooked up all the solenoids to the harness (but not vacuum lines) and that fooled the ecu not to go show codes. We could not overcome limp mode, even then.
Go to Power FC sooner than later.
Maybe also run a smoke test to see what leaks you have.
We had a case where a guy's intercooler pipping was collapsing. Seems some aftermarket cheapo pipping had been subbed in at some point.
None of the "intercooler" hoses are accordion style. I think what you are talking about is your intake tubes are collapsing which would mean a restriction in your air filter and would definitely cause this. What kind of intake are you running? If you are on the stock intake box, I would pull the two accordion hoses off of that box and rev it to see if you have the same issue. Most likely there is a blockage in your intake box or your air filter itself is really dirty.
Attached is a picture of the engine bay. Circled in red is the accordion connection I was referencing that will collapse under engine vacuum. The intake setup is from a V-mount that I bought used from Japan auctions so I doubt that is the restriction (I am aware of hot intake air from the radiator). Also, this just happened overnight. The car drover perfectly for months of tweaking things then everything happened essentially from parking to driving the car a week later. I had been driving the car fine without issue with the check engine light on and all codes for all those months which is why I was having a hard time believing it was limp mode, but it's possible the ecu takes a certain amount of miles to trip limp mode? Anyway, appreciate the help and I'll try and get the PFC installed to see if that changes anything.
I'll also try and take note of engine vacuum during some testing as well as run a baseline compression test. I do have new plugs/wire installed and I did the FSM check on the coil packs while I had them out during my initial rats nest rebuild which all tested good, but they do have 87k original miles on them.
It would take a lot to collapse that pipe unless its really soft. The stock ECU definitely doesn't like to have all of that removed. You may be pleasantly surprised with the power FC installation is my guess. Usually with limp mode it will pull a ton of timing which would explain some of your symptoms but I've never seen that pipe collapse without a restriction, especially if you say you have boost coming from the turbos when you pull the pipe off. I have run across on multiple occasions where people leave rags in their pipes and I find them down the road in intercoolers. They tend to make their way through slowly sometimes before they hit the intercooler
Stock intercoolers can be had cheap. maybe swap yours out. I have about 15.
Hard to imagine where such a severe blockage could occur to cause the vacuum to collapse that pipe..
It is unlikely that your turbos have seized in place?
I see that at sometime someone has swapped in a S8 y-pipe and crossover pipe.
The disc shaped valve plate in the back half section of the y-pipe might still be there and jammed shut.
It is also hard to imagine that the stock ecu could tolerate so many deletions, but, as a matter of fact, my stock ecu would reset and I could bomb around a fair bit before it would throw the car back into limp mode (often in the middle of an intersection).
I am talking an RHD car. I am not familiar how limp mode works in LHD.
For RHD, the cars did not have a check engine light. Limp mode was the way the car told you to go for servicing.
I have seen instances where, for whatever reason, shops have swapped aftermarket ecu internals into a stock ecu casing.
S
I am talking an RHD car. I am not familiar how limp mode works in LHD.
basically the same. the ecu looks for open or short circuits for everything, and then some things like the OMP have actual target values
the list of stuff that will set a limp home is in the manual, the TLDR is anything to do with boost control, fuel delivery or the Metering pump.
This thing (for reference). Often this charge control valve is removed in simplified ("parrallel") twin turbo set ups. Mine was removed and the opening the actuator worked through was left open with a small screen. When I covered the hole the car would not run right. Somehow the stock ecu was sensitive to even that small difference in air intake.
I am suggesting that that plate may still be in your lower y-pipe intake and somehow jammed shut. That would prevent air from the rear turbo that the ecu might be expecting at 4500 rpm.
If you still have the actuator there maybe it is not getting vacuum (is that solenoid one of your "codes".). If so the valve might not be opening as expected.
So to add a little more detail. Over the last year I pulled the upper intake and chased a fuel leak that was a torn hose between the primary and secondary injectors. During that I pulled all the injectors, inspected, ohm tested, (did not flow test) and then replaced all o-rings, seats etc for the fuel system along with the FPD. Not wanting to put all the solenoids and rats nest back in I deleted a lot of the emissions equipment. Put all the blockoff plates in, but did not trick or put resistors in any of the plugs since I had already bought the PFC. Also deleted the ACV, air pump and accelerated warm up system hence all the codes.
I also installed the y-pipe along with an HKS downpipe while I had lots of things torn apart.
I have not had a chance to work on the car yet since posting, but I can confirm that the valve in the y-pipe does function with the key on/key off with vacuum in the system. I can physically see it move so I don't believe that is stuck.
This is a new one to me so I'll definitely keep this post updated when I find what the issue is. I did try and take a video of the hoses collapsing, but once the car had sat for a bit they didn't collapse like they did after driving the car.
OK, Problem Solved!! And to add, I am an idiot, but I'll get to that. Short version it was the cone intake filter which had slid onto the intake pipe further essentially capping that front side turbo from breathing.
So essentially, the engine could not breath and being around many engines that have had rags in intercoolers, plugged exhausts I knew air couldn't move, but for the life of me could not figure out why? Things that I tried:
Pulled all intake piping looking for blockage, didn't check filters.
Pulled the exhaust, cat and muffler to inspect.
Checked compression - good, right around 100 psi, however only used the cheap manual method as I don't have a rotary tester yet.
Checked timing and ignition
Pulled and cleaned all grounding points. Almost purchased a full grounding kit.
Checked fuel pressure
Pulled intake hoses and manually spun the turbo by hand. Was good.
Installed the Power FC since I had so many codes. Didn't change.
Once I installed the Power FC and things didn't change and showed no real sensor value issues (thought maybe tps, but showed perfect voltage through range) I decided to pull the intake cones just out of curiosity. Well low and behold the filter had slide down the pipe plugging the hole. Essentially like sucking through a straw and capping it with your finger. Lesson learned on this one for sure, but back up and running. If anything I know the car is in good working order. Sheesh
Intake filter blocking end of pipe Internal cone that blocked the end of the pipe
Case closed and lessons learned. Thanks for al the input everyone, stupid mistakes make for long days.
OK, Problem Solved!! And to add, I am an idiot, but I'll get to that. Short version it was the cone intake filter which had slid onto the intake pipe further essentially capping that front side turbo from breathing.
i've done that too! i also have the shirt for doing that with a fuel pump too. glad you fixed it, its not easy to find something like that
11-16-23, 05:50 PM
