Hey guys, I bought a modified '94 FD a little while ago and have been hunting down a problem. I recently added an A/F sensor and gauge to aid in this mission, and figured it was time to ask for some opinions on what might be going on. The previous owner suspected the car was tuned too aggressively and that it was running lean at startup, but the opposite seems to be true. The existing tune for the car seems to be okay based on the dyno run sheets I have from him, it has a much more healthy/rich A/F under throttle. I am unable to verify this tune on my own.

What I'm experiencing:
- Rich idle (10-11 A/F)
- Lean WOT (~15 A/F)
- Fine cruising (12-14 A/F)
- Needs to warm up for a couple minutes before being driveable, otherwise it will stall under any throttle
- Second turbo doesn't seem to provide any 'oomph' when it ought to be coming online
- Throttle 'blip' results in the engine bogging, then recovering to rev up after a moment
- WOT will hesitate and then respond like ^
- Nice gas smell all the damn time, from rich idle
- boost target is 15psi, and I don't seem to be hitting that reliably
- car seems to have been tuned without the BAC plugged in, it's unplugged and starts and idles okay. If I plug it back in, the idle at startup jumps to 2k and then after driving it will bounce back and forth from 1k-ish to 2k-ish constantly


What I've done:
- replaced plugs and wires (plugs were pretty black)
- checked coils
- verified the condition of the injectors
- replaced the fuel filter
- verified TPS (using PFC) - very slightly out of range
- verified MAP (using PFC) - very slightly out of range
- visual inspection of vacuum lines and solenoids, including under the UIM (actually tested the solenoids)


Modifications to the car:
- stock twins (simplified sequential)
- aftermarket rad and intercooler
- custom intake + piping
- downpipe + 3" exhaust straight back to muffler (no cats)
- Power FC + commander
- simple water injection, comes on under boost of ~8-10psi, just water
- HKS twinpower
- aftermarket clutch and lightweight flywheel (not terribly relevant)

I'm still learning about this car and how it works. I'll probably be taking it to a shop that knows rotaries to have them take a look at it once I have some more money saved up, I'd rather show a little humility than blow up my engine. But in the meantime I figured it couldn't hurt to hear if anyone had some thoughts. I'm sure I've forgotten something, ask any questions or for any additional info.

 

Additional details I somehow neglected:

- Streetport
- Larger injectors

 

Sounds like your tune. I assume you are on the base map?

 

I'm not on the base map, I actually have a tune from relatively unknown origins. I have the 'log' from the most recent dyno run, I'll add scanned images tomorrow.

My assumption was the tune as well, but I don't know much about tuning I'll admit. My instinct was going off the graph from that dyno pull and the cold start issues. I'm not convinced the tuner knew what they were doing, maybe just enough to make it run tolerably and show impressive numbers for hp + torque.

 

I'd take it to a competent tuner asap.

 

Have you checked the vac referrence to fuel reg?

 

Sounds like your tune, did the previous tuner tune for the water injection or was this added after?

 

Hi

Maybe try to add some fuel on the inj vs TPS table . This way you can add fuel dependent on throttle position .To get from 15 AFR to about 12 AFR requires quite some additional fuel (about 25 % percent according to the excel calculation ) .
Maybe speak to user arghx . He is really good with the power FC and also runs the power FC tuning group on yahoo .

 

I have not checked that vacuum line specifically, I will.

The water injection has been there all along, I believe. The tune was targeted for 15 psi and I'm pretty sure the PO had the WI there to make that safer.

I'll take a peek at some of those values, but I don't have a datalogit so I'm kind of limited. Also I'd prefer not to fck it up more..

I've been trying to get in touch with synaptic3 as they seem like the closest place, but they don't really get back to me. I heard back once, and now it's been like 2 weeks. And they're 3 hours away..

I'm in Burlington Vermont if anyone has suggestions!

 

That vacuum line seems good.

Additional information from puttering around this evening: the car seems inconsistent in its boosting. Sometimes won't go above 1-2 psi sometimes goes up to 12ish no problem. Not seeing it get to 15 at all.

Still looking to get it tuned if anyone has suggestions.

 

This seems like a very logical troubleshooting step before adding fuel.

 

on the power FC check the injector duty , and check what CC injectors are on the Power FC , the stock injectors should max out at 14psi , you said you are running 15 . was the PO running meth as an added fuel source? ( this could be the missing factor) BUT lets assume someone messed up . as that is almost always the case .

honestly I think you need to take the car to a tuner .

another question for you is your fuel pump is it stock ? has it been re wired .. I started having lean issues with my fuel pump . and it ended up being the wiring . did fp rewire and the car instantly went super rich ( I had continued to add more and more fuel to the map )

 

Is there a specific procedure for checking that vacuum line? I didn't find anything scouring the FSM but it is pretty massive so I could've missed it.

I'll take a peek at the fuel pump and associated wiring tomorrow, I am unsure if it's been upgraded or modified. I do know that an anti-surge kit was installed in the tank so there's a chance something got buggered then.

I'm glad we can all agree it needs to visit a proper tuner, just need to make sure it survives the 3+ hour trip to the closest one I can find otherwise it's pointless.

 

Sorry didn't read your turbo problem before i spoke about adding fuel based on TPS . Can you describe your boost pattern a little bit more ? Do you ever get boost of 8 PSI or higher below 3500 rpm ? Does your boost come online when you blip your throttle ?

 

Update: I browsed through the PFC commander view of the injector map, and it looks like for some reason the entire area where the car is above ~3500rpms and has positive boost the fuel is set to cut back, decreasing to a lowest value all the way up to max boost and rpms. This seems totally wrong to me, and to me it pretty well explains why the car leans out so badly..

 

So did you add fuel to those cells and see what happen?

 

I didn't notice a difference making changes in PIM Voltage, which should increase fuel across whole rpm ranges. So I observed where I was on the map trace and make some changes in that area of the INJ table directly. I saw a drop in AFR on my wideband gauge after doing so, and have now bumped a good portion of my map based on others I was looking at online. Previously I was seeing AFRs of 14-16, and now I'm seeing 11-13 under load. I ran out of time today to keep going, so I'll continue another day to add a bit more fuel to the map, I'm trying to do it incrementally.

I also modified the water temp correction and the idle is reliably above 11 AFR now which is an improvement, it's also much smoother.

The car runs much better. It pulls like it ought to. I guess the tune I have logs for isn't what's on the PFC or someone made changes. I'm bummed that the guy I bought it from didn't just tell me that.

Anyway, I'm calling this resolved. I'll be able to get this car to a tuner at some point now without worrying and it seems to run much healthier. Before getting tuned I'll also probably redo the vacuum lines on the off chance there's a bad one contributing to all this.

 

Power fc tuning group is a great resource for learning about FD tuning.