Car wont go over 3500 rpm !!

[Cornflakes_GLHT]

90 daytona VNT
fresh engine rebuild (spun rod bearing #1)
worked perfect until 2 weeks ago.

here is the problem : the car wont go over 3500 rpm !! feels like engine is cutting/missfiring and it wont go ! it happens when rolling, boost, no boost, stoped and reving engine, even when downshifting ... will not go over 3500rpm

i checked everything the has to do with ignition. remplace everything (coil, wires, plugs, cap,
replaced gaz filter
i dont get any codes (exept 33-35, fan relay (i have a switch on it and a/c relay - non existent anymore))
i dont think its anything with the exhaust, i dont have any smell or anything.
i check fuel pressure and its at 45-47 lbs at the fuel rail

heres the thing ... plugs are really white... but the engine does its rich / lean normaly and the o2 sensor is working fine between the normal range of voltage ...

ANYONE !?!?!?

thanks a lot for any suggestions / idea

pascal labelle
86 glht
90 vnt daytona

[tryingbe]

Have you check your timing?

[Cornflakes_GLHT]

Quote:

Originally Posted by tryingbe Have you check your timing?

yeah i did ... set at 12 degres

[Shel-Game]

Sounds like the rev limit when a bad TPS is detected. Check/replace your TPS.

[tryingbe]

What about the cam timing?

[RampageTurbo]

I had the same thing happen on an N/A Horizon of mine. First thing I found was that it had jumped time. When I got that corrected I pulled the rocker cover. It has a slider cam and the slider pad on one of the exhaust valve rockers had popped off. The rocker had gotten cocked sideways and the valve wasn't opening fully. It was freak but it might be a possibility.

[Dave Carpenter]

Had a similar problem in my Charger and it turned out the logic module was acting up. Pull the battery cable for 10-15 minutes and hook it back up to reset the Logic module. Each time I did that, it wa fine for a few miles, then it would act up again. I had the Logic module reprogrammed and it' been fine since.

Dave

[Cornflakes_GLHT]

thanks for the ideas

but the TPS is fine, i have a ODB2 scanner and i can check all the sensors .. and TPS works fine.
i will check cam timing just to make sure i didnt skip a tooth.
ill get back to you guys with this .... too weird !!

[Cornflakes_GLHT]

OK .. update on this .. if anyone has some new ideas

cam gear is fine. its on top when #1 is at TDC

i also checked the injectors... all fine. the spray is nice

and I still cant figure out why my car is so lean .. the plugs are really white and on the scanner, the "adaptive fuel" is at -21% ...
the way i figure it is the car is really rich and the computer is trying to lean it out and does it too much. but what would cause the computer to think thats its really rich ?? o2 is working fine. so is the map ...

any ideas ... im running out of them over here !!

Also ... it got worse yesterday .... now it wont go over 3100 rpm !!

thanks again

[Cornflakes_GLHT]

Update on this issue :

unhocked the downpipe and tried it again (in case of a blocked cat)... same problem ... car just cuts at 3000rpm
also tested all wires for the ignition and grounds ....

the only thing left to check is to remove my valve cover and see if there is anything loose in there ...

if anyone has ideas im really open to them now ....

im just praying its not the computer ... try to find a VNT computer in ontario/quebec !!!!

thanks again

[Phreakish]

check your fpr, I had the SAME issue with a bad FPR.

[turbovanman]

Check your HEP or coil!

[sdac_guy]

With the engine cold, reach behind the intake and make sure you can move the VNT actuator arm up & down. Then have someone start the car (while you hold the actuator arm) and make sure the arm "centers" itself when the car starts.

I had a very similar problem on my 90 Daytona VNT. It would only happen when I was hard into boost for a bit, then when I let off and reapplied throttle there was no power and it would not rev over about 3500 with the clutch in. When driving it was next to impossible to hold any speed at all as the power was really off.

Mine would always clear up though, after a couple minutes of driving or idling. When I replaced my turbo because of a bad oil seal leaking into the intake side, I found a lot of cracked vacuum lines which I replaced. The problem has never come back.

Whether it was the vanes in the turbo sticking shut (blocking exhaust) or something caused by the leaking vacuum lines, I don't know. But white plugs can be a symptom of plugged exhaust (blocked cat, or on a VNT, vanes shut).

When I had this problem, someone suggested to me that I had a blockage in the intake tract (bad air filter, etc), however if that were true, I would have had some vacuum on my boost gauge even with the throttle at WOT as the engine would be starved for air. On mine, cracking the throttle at all while the problem persisted immediately caused the vacuum on the gauge to go to 0, but boost would not build at all.

Barry

[DirectConnection]

Quote:

Originally Posted by sdac_guy Whether it was the vanes in the turbo sticking shut (blocking exhaust) or something caused by the leaking vacuum lines, I don't know. But white plugs can be a symptom of plugged exhaust (blocked cat, or on a VNT, vanes shut). Barry

Barry, I had a bad vane actuator on my VNT that wasn't functioning properly. It was doing as you described.... keeping the vanes shut. But, my plugs were BLACK from being rich. It wasn't able to burn off the fuel due to poor scavenging. After having the car idling for sometime trying to diagnose what's wrong, the car would eventually foul out the plug entirely. I would have to buy new plugs and squirt oil in the bores to bring up enough compression to run again. This car would not rev over 3k and would also build boost in nuetral. Ran like it was on 3 cylinders the whole time. I swapped it out for another used one and even now, I occasionally have to pop the hood on my car and give it a little nudge. After that it is fine.

Do as Barry suggests and feel the actuator rod when someone starts the car up. Be real careful as the back of the intake may slam your arm against the firewall if not enough room when starting. One of my VNT Shadows has room, the other doesn't.

[sdac_guy]

Quote:

keeping the vanes shut. But, my plugs were BLACK from being rich. It wasn't able to burn off the fuel due to poor scavenging.

What you say here makes perfect sense. I never checked the plugs when my Daytona had the problem. But 20 years or so ago, I had an Omni that had a plugged cat. The plugs on that were white, and I was told it was because cylinder temps were so high from the burning mix not being able to get out through the plugged exhaust. But that may have been a different situation entirely as you point out.

Barry