Limp mode after clutch r/r...
 

Hey all - I'm a bit perplexd by this one and wanted to see if I could get an opinion of the collective wisdom.

Car is a 1990 S2 Cab with an 89 Turbo S engine, exhaust, computers and all that jazz. Turbo Cab so to speak. When I pulled it out of storage, my release bearing was making all sorts of sounds, so I decided to do a clutch in it before the real driving season started. I put a Cup clutch in it.

After putting it all back together, and taking it for a ride, I get no more than 1.2 bar of boost. Limp mode. Here's what I've tried so far:

1. Replaced the TPS - as I had hunting issues before the clutch job.
2. Replaced the CV - as I broke a nipple off it during the clutch job.
3. I get no blink codes out of the KLR, though when I pull the TPS connector, I get 4-1 and 3-3, which is correct. I know I need to test it after a drive, and not shut the car down first. ;)
4. I clamp the line going to the wastegate control nipple, and get all sorts of boost. So the issue is in the CV control circuit.
5. All 3 grounds are connected at the back of the block (bellhousing).
6. Battery is good, and I get 13.6 volts to the CV voltage line, and can see the voltage flutter (other side - control line - goes to ground) when I move the throttle past 65 degrees.
7. WOT works fine, KLR shows that it sees WOT.

As the car starts and runs just fine, I don't quite remember anything else I need to check.

I also checked all of the air hoses, and they're good, also proven good by the fact that I get all the boost I want when I clamp the wastegate control line.

I'm beginning to suspect the KLR itself, but it does give me blink codes and seems to work just fine.

Anyone have any thoughts?

Thanks in advance.

The new clutch might doing some extra noises taken for knock by the knock sensor and the KLR might therefore kill the boost.

Check the vac hoses on the CV, and make sure they are plugged in properly. Sounds like you might have them reversed.

Knock wise - the KLR assuming it works fine would throw an error code for that. CV wise, I went hose for hose for the connections, so they should be fine.

Do you have a boost enhancer or MBC you can swap for a test? It sure sounds like you have a bad CV again if you can clamp it and the WG holds. I have read several times here where the plastic CV bodies, even on a new one, leaked. This would definately cause what you might assume is KLR related limp mode since the result is the same.

Interesting thought....
 

Interesting thought, that the new valve is bad potentially. I had thought the same myself, so I did check the resistance of the valve, and made sure it actuated too when I applied voltage to it - and it did, though the first time it didn't move. It does click all the time now...

I do have a MBC here, that I bought just in case. I'd much much rather have a working 'stock' setup though. Call me a purist now, but I did have a 426HP 951 a few years back...

I'll email the folks that supplied the CV to me, and see if they'd send me another one to test with and such. They're very stand up folks, so let's see.

Hi Toolmaster
I have the same issue, and I am trying to solve it. I bought two new CV's, and I now have 3 good working ones. I think the issue is a poor wire connection somewhere. I replaced all vacuum lines, cleaned the metal lines, replace the CV, TPS, and knock sensor to no avail. I have done all your tests, and even had the two brains checked by ECU doctors in Fort Lauderdale.
However, I have temporarily fitted a Lindsey Boost Enhancer, and my boost is now okay. This device stops boost pressure from getting to the CV until 10 psi is reached. So, once you are past 10 psi, the boost air gets to the CV. I have no idea why this makes it all work.

Like you I am a bit of a purist, and the CV was put there to protect the engine. I agree you can put on manual boost controls etc., but that evades a problem. I am thinking of putting in new wiring from Lindsey, as I really can not see the cause. I believe that a sensor is not being picked up by the ECU or KLR, but I don't know which one. It is probably not the ECU, KLR, Knock, TPS, but it could be crankshaft, heat etc.

I have to agree that maybe you are getting a knock somwhere, but none of us have the equipment to detect what is normal.

Philip

Philip - Knock wise - assuming engine knock is the cause of the limp mode, then technically the KLR would blink code it. I know you can knock on the head with a screwdriver while it's running and see on an O-scope the ignition and timing changes, so I have to think thats a potential, but a small potential at best.

Part of me is rethinking the idea of it being the speed and/or reference sensors. They really were the only ones I checked and moved during the clutch job. But I don't fully see how they would limit boost, rather than just cause a no start, or poor running.

Philip - silly thought... Did you also replace the hose from the CV to the wastegate with a smaller diameter silicon hose?

Hi Toolmaster

There is an item somewhere, either here or elsewhere, on the connectors for the speed/reference sensors, that suggested the contacts were not good, and they recommended replacing the connectors with different ones. I cannot remember where I saw it, but it was in the last few days! That is what got me thinking about replacing the old wires, which as you say you had to disconnect.

I replaced every hose with a set created by 944online, and that included the original P hose from the CV to the wastegate.

I had also heard that the blink codes are not all that reliable. If you had access to "The Bosch Hammer", or even the modern equivalent, it could be sorted, as they will give you the knock sensor input, and compare it to what it should be. That is, according to the P manual, which I have and is upgraded to 1989. I know in my car, that when I get to about 2800 rpm, there is a vibration somewhere ?heat shield, engine mount?, but that might trigger the knock sensor. I tried leaving the sensor off, and no change.

Philip

I was hoping someone like you, might come up with an answer.

I don't think anything in the ref sensor plugs can effect the knock sensor or KLR for that matter. It can prevent stable power to the DME relay and cause fuel issues if loose but his car seems to run fine other than the usual 1.2 bar boost issue. I think the bad KS or CV wiring might be a good start. Just for jollies did it run correctly before the clutch job?

Philip - all hope isn't lost yet. I have an O-Scope coming soon, hopefully friday, so I can start delving into what the heck is going on. I had hoped I forgot something 'silly', and really had hoped that clamping the wastegate hose would have still given me low boost.

Yes - it ran perfectly before the clutch job - boost was there, other than a hunting idle at times on return to idle speed, which was corrected with a TPS replacement.

Hi Toolmaster et alii
I have an old 1995 Snap-On O'scope, but I am not sure of the wave pattern for the knock sensor. The manual says hit it and see the result, which looks fine, but I am not sure how you check it with the car running, short of piercing the relevant wires, which may harm them? And even then, the P manual does not give you a picture of the wave form with the car running. I am interested to know what you find. You can bet your bottom dollar it will be something very simple, but I do think we are on the right track.
Philip

Ok - who can test something for me???
 

All -

Started troubleshooting once again, after one of our Rennlist sponsers was very nice and had a discussion with me via email. (Thanks John!).

Could someone un-due the banjo bolt connection, and also the small return line connection into the J-boot from the CV, and blow through them with their car OFF? And then the same test with the car turned on (but not running)? I'm wondering if the air goes from the banjo bolt, through the CV, to the J-boot, or if it goes to the WG.

Have to run to my eldest's middle school night tonite, but will be continuing later... Many thanks!