Can't figure this one out - need help. Car is running rough like one cylinder isn't firing and the brakes aren't getting a power boost - just manual. No engine codes are being set. This after the following maintenance - before the maintenance everything was running great.

Changed the oil last weekend and put 7 qts of oil in the case (Mobil 1, 5w30). Also replaced a leaking inlet pipe and top radiator hose and refilled the radiator with Dexcool/water (50/50). I checked for leaks after changing the oil and inlet pipe and everything ran fine - no leaks. Afterwards, the oil was just above the "low" indicator so I "topped-off" the oil with another quart. Seems about a 1/2 qt above the "max" indication on the dip stick now. I also topped-off the radiator and spilt about a cup. Cleaned-up what I could - did not start the engine assumed all was fine.

Next day started her up to go to work, and as I pulled out of the garage, she started running rough and I had almost no braking power! Managed to get her back in the garage carefully. Have reset everything (neg lead off batt for several min) but problem continues - no codes are being set?? Still runs rough and no power brakes...help!

Vacuum lines?? injectors?? I don't know where to begin.

 

Sounds like a serious air leak (after the throttle body), maybe even the vacuum line to the brake booster. That would cause no brake power and rough running, as you get false air into the system.

 

Assuming that you can get some reasonable RPMs (even with the rough running), It would have to be a Major Vacuum Leak. Probably a loose or broken Vacuum Hose.

The Power Brakes are Vacuum Activated.

 

I don't know anything about XK8s in particular but I agree that it sounds like a major air leak.

FWIW, the first thing I do in similar situations is re-trace all my steps and see if anything was inadvertantly broken or knocked loose during the course of the repairs. It can happen to anyone.


Cheers
DD

 

With a mjor vacuum leak you should hear a pretty loud hisssing sound as the air is sucked into the system.

If car ran ok before you cleaned up the coolant spill, you may have broken a vacuum hose or plastic connector, they fall apart pretty easy after a few years of heat & cold.

Start the car with the hood open and just try listening for a hiss of sucking air.

To lose the brake boost it would have to be a major vacuum leak and you should be able to hear that and locate it.

Good luck.

 

Thanks for the help....found vacuum line on right side of throttle body disconnected. It is a rubber hose slipped over a hard plastic line maybe 3-4" long coming out of the throttle body. It is secured with a ty-wrap! Just reinserted the hard plastic line into the rubber hose with the ty-wrap on it and everything works fine again. There is an aluminized wrap over the line to protect it from heat I suppose. Is the ty-wrap correct or should I put a clamp on it?

I must of pulled or pushed it loose while reinstalling the air duct over the throttle body... I had replaced the cracked bellows a few weeks ago and needed to adjust one of the clamps on the new rubber bellows so I took the air duct off and back on right after I changed the oil.

Thanks again - btw - the wife located the leak for me - I can't hear worth a damn.

 

It was the brake booster vacuum line...traced it back from the booster to the right side of the throttle body.

 

Glad it was so easy to find & fix.

I have done that myself with other cars and it can really ruin your day.

 

Just curious...aren't these supposed to take 6 qts, and not 7? Did you allow time (at least 20 minutes) for the oil to drain down into the pan?

 

Click HERE for a good thread on oil levels for these engines and how they have evolved over time.

 

Very interesting about the dipsticks. I looked at mine (97) and there is not only NO part number, there is no crosshatched portion....just two holes to mark "low" and "high" I guess. So, if I put in 7 and it stays at the top hole am I really at the minimum under the newer specs?

 

It would appear so. My dipstick is exactly like yours, and I fill to 8, with the oil on the stick about the same distance above the top hole as the distance between the two holes. So in other words, the top hole is halfway between the bottom hole and the oil line.

 

OK. Do you use any oil between changes? I know I lose a little out the VVT seals in front, my next little project.

 

I've only had the car for a few months, but no...now that I've replaced the cam cover gaskets and addressed a couple of other things (to be posted on later), the engine is tight, doesn't leak and doesn't burn oil. For now!