computers pulling boost/timing...I'm stuck!

[Pettybird]

A couple weeks back, the car started going into limp mode. I'm more than a little frustrated after laying out cash and a couple days' worth of work to no avail. I'm ASE certified, have worked as a parts counter guy and a service writer, and I'm still stuck saying "all of a sudden, it just happened." I couldn't find any odd issues with wiring (that I can see on a fully assembled motor) and I didn't do anything to the car to precipitate the change.


Symptoms:

Even with the WG line pinched, the boost gauge is really sluggish and only reads to 1.6bar when, prior to a couple weeks back, it would peg at 2 bar (autothority stg.2 chips.)

I pinched the wastegate feed line from the cycling valve. The car's a little faster that way, though not as it should be--I'm thinking the reduced timing is still killing it, and the boost gauge still doesn't peg.

It's definitely going into limp mode--there's a decrease in power you can feel, then a BIG drop when the boost drops to 1.2 bar. I can activate it on the freeway, cycle the key, and power returns for another 8-10 seconds.



Here's what the problem ISN'T :

The first thought was bad gas, but I ran the tank empty and refilled it with Sunoco 94.

I checked the vacuum lines, and all are connected. I played around with a bunch of them anyway--the connectors are horrible after 23 years, and new ones from the dealer are now at my house. I can't see any that have fallen off or broken at this time.

Replaced the BOV with one of those fancy billet ones--I had it lying around anyway.

Replaced the charge pipe couplers

Replaced the hose going to the cycling valve--it was cracked.

Replaced TPS with a known good piece

Replaced the KLR with a known good piece

Pressure tested the KLR signal line with vacuum from a mightyvac pump--it held. I could not find an issue with the hose itself.

Pressure tested the fuel system--30psi with the vacuum line connected and 34psi disconnected. Pressure holds steady when revving engine. I'm still running the stock FPR, so this seems normal.


Still nothing! Anything else I should check? I need to get an LED so I can check the KLR codes, but it seems like I've covered everything else...


Thanks

Doug

[Techno Duck]

Only other thing i can think of that would cause limp mode is a faulty knock sensor.

[JoshB]

Originally Posted by Techno Duck

Only other thing i can think of that would cause limp mode is a faulty knock sensor.

I like Jon's idea. Wonder if a faulty oxygen sensor could cause that well?

[zedsn]

I live in your area and have a spare 1989 DME and KLR that you could try to see if that fixes your problem.

[zedsn]

You can run your car with the 02 sensor unplugged. It will run fine just give you a little worse gas mileage.

[kdjones2000]

What about your cycling valve, have you checked it out? I guess that it should not be the issue if you have the WG line pinched, however.

Do you still have the original chips for the DME/KLR? Put those back in and see if things get better or not.

What about the spark/distributor, did you check the rotor and all of that? I would go through there and make sure that things are in order if you haven't.

Agree that sounds like you have most things already covered.

Good luck, Keith

[Pettybird]

thanks for the suggestions. A question about the knock sensor--would it start pulling timing boost right away? i would think (and I could be completely wrong) that it would allow full boost and then go 'whoa' when it saw something it didn't like.

Keith--the plugs, cap and rotor were changed last fall (15 months ago). They're on the list to check, as well. Would poor spark lead to low boost? Again, I'm just asking.

Thanks

Doug

[Techno Duck]

Dont quote me on this, but i believe the throttle position has to be >60% for the KLR to pull timing, or that is atleast what i think the manual test point describes. You may want to ask this on RL as i am sure either RougeAnt or John @ Vitesse can tell you.. these guys are probably the most knowledgeable about proper operation of the factory boost control.

When the car feels like its operating in overboost, is it immediately while boosting the car, or will the car boost correctly then revert to overboost? Does the car feel sluggish even at part throttle or only WOT? Does this happen only when trying to hit full boost or also at partial boost (say 5-9psi).

Do you have access to the Turbo factory manual? Look at pages 28-30 though 28-35, specifically test point 12 for the knock / pressure control.

[nize]

water in the tank can cause limp mode.

[Pettybird]

that makes sense, but I've been driving it daily for over a month now (and all last summer) and have to refuel every week. This is the second tankful of fuel from a second source...that would be some rotten luck.

[Pettybird]

Originally Posted by Techno Duck

When the car feels like its operating in overboost, is it immediately while boosting the car, or will the car boost correctly then revert to overboost? Does the car feel sluggish even at part throttle or only WOT? Does this happen only when trying to hit full boost or also at partial boost (say 5-9psi).

Do you have access to the Turbo factory manual? Look at pages 28-30 though 28-35, specifically test point 12 for the knock / pressure control.

When I got the car it had a broken cycling valve so I had all boost, all the time. That caused the KLR to do the severe cutout after only 10 seconds or so of boost. This time, max boost never happens, and after 15 seconds or so it pulls it back to 1.2 (on the gauge.) If I'm on the freeway for a while I can get more boost again for the same amount of time--it does reset.

the car's not 100% happy off boost, either, but it's not much worse than it was. I do occasionally have a 2000+rpm idle, too...I think it's time to pull the intake and change more stuff.

[kdjones2000]

This is what the LR site says about bad wiring to the knock sensor:

The knock sensor portion of the harness also sits in an extreme environment and suffers the same fate as the fuel injectors wires. When the wires become brittle and break, it's like having a bad knock sensor. The car will pull back the timing all the time. It can make the car's power come on lazy and cost you horse power as well.

Sound like what you are experiencing?

[Pettybird]

yes. I've been looking at the LR harnesses, too...


I have a spare parts harness--maybe I can find the cleanest AMP connector on it and splice it in as a test.

[Pettybird]

I replaced the knock sensor with a new Bosch piece, chopped off the connector and installed a brand new end with pigtail, and the boost problem persists. It does seem to drive better off boost, though--I wonder if it was problematic for a while now...

I also unplugged the O2 sensor with no change. I'm 2 tankfuls of fuel further along, too--it's not the gas.


What else am I missing??? In theory, I could STILL be having an issue with the knock wiring, but it seems less likely with a new end. the wires weren't horrible when I pulled back the insulation, either.

[zedsn]

I live in Westlake and have a known good KLR computer box that you can borrow to see if your problem is the same with a different box.

[Pettybird]

I appreciate the offer but I bought an extra KLR and it made no difference...I used my same chip, though. maybe I should just install another and see what happens.

[zedsn]

I have a stock box with stock chip if you decide that you would like to try this route.

[rick13]

Can we get some actual experiences/symptoms? Like "my foot is in the gas and at 3500 rpm and 14 pounds of boost the engine...blah blah blah"

You are leading the witness right out of the box. We all have preconcieved notions as to limp mode. Maybe its not limp mode at all.

Leaky injector?

[jvillanueva944]

did you ever find a solution to your limp mode issue?

[jkb58]

What he was describing was not limp mode. W/ the pinched/closed control line to the WG, it will generate a lot of boost (20+ psi) even if the KLR is in limp mode. Based on what he wrote, it would appear he had another problem w/ the actual WG or turbo itself.