Mysterious running problem 850R 1996 Help advice please

Ok..so as I said car ran a treat for 1500 miles recently in 4 days or so..then pulled out to overtake and at around 3000rpm it was like I'd hit a rev Limiter.
Got home fine but felt that the engine bay was a little too hot?
Not used any water or any oil
The car is an Automatic and If I put her in "N" it will rev off the clock no problem at all
Put the car in "D" and it runs fine a little erratic at tickover when warm but always runs but always has the rev limiter moment at 3000 and above.
I had a Bosche Lambda so I fitted that..no difference
I have removed all the plugs and they are all the same colour..almost white actually...which again makes me think it might be running a little hot?
I have cleaned the MAF etc
I have a clean air filter
Any advice much appreciated
Bonnietiler

Any error codes?

I'd try an ECU reset first...

Quote:

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Originally Posted by bonnietiler

Ok..so as I said car ran a treat for 1500 miles recently in 4 days or so..then pulled out to overtake and at around 3000rpm it was like I'd hit a rev Limiter.
Got home fine but felt that the engine bay was a little too hot?
Not used any water or any oil
The car is an Automatic and If I put her in "N" it will rev off the clock no problem at all
Put the car in "D" and it runs fine a little erratic at tickover when warm but always runs but always has the rev limiter moment at 3000 and above.
I had a Bosche Lambda so I fitted that..no difference
I have removed all the plugs and they are all the same colour..almost white actually...which again makes me think it might be running a little hot?
I have cleaned the MAF etc
I have a clean air filter
Any advice much appreciated
Bonnietiler

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Do you normally open the bonnet just after you've been on a run in the car? Doubt it.....so just because you've opened the bonnet on this occasion, why would you suddenly think it's running too hot?

Trust your gauges! If the engine was running too hot it would stink!!
I bet your temp gauge was normal...bang in the middle? Cooling fans working ok, they may have even been running when you opened the bonnet??

You've really nothing to worry about. As KMB says, get your codes read and go from there. From your description of the symptoms, sounds to me like your car cut the fueling because of an overboost situation.
Look for vac leaks and or hoses not fitted correctly. A vac leak doesn't always put the EML on but you should pull a MAF code or O2 sensor Bank 1 code if your running lean or air leak.

Idle should be stable, not erratic, even in 'D'. It should just lug down to about 750 rpm but still be stable.

No error codes.. definite feeling of heat from under the car to be honest, I have had a Lambda light on but it disappeared after around 200 miles (Fort William to Lancaster)

Is this the same issue as the suspect CAT? A collapsed car would cause hot exhaust gasses to build up - and the areas around the cat would get hotter as the heat will radiate from the hot spot.

To be honest that is my thought, but I would like to know how to check that my Cat has actually failed before buying a new one?
Any Ideas?

EXHAUST BACKPRESSURE CHECKS

To diagnose a plugged catalytic converter, you can check intake vacuum or exhaust backpressure. To check intake vacuum, connect a vacuum gauge to a vacuum port on the intake manifold. Start the engine and note the vacuum reading at idle. Then increase engine speed to about 2,500 rpm and hold steady. Normal vacuum at idle for most engines should be 18 to 22 inches Hg. When the engine speed is increased there should be a momentary drop in vacuum before it returns to within a couple of inches of the idle reading. If the vacuum reading is 10 percent lower than normal and/or continues to drop as the engine runs, it probably indicates a buildup of backpressure in the exhaust. Remember, though, that intake vacuum can also be affected by retarded ignition timing and valve timing. What's more, some engines are much more sensitive to small changes in intake vacuum than others, so checking backpressure rather than intake vacuum may give you a better indication of what's going on.

Checking backpressure requires connecting a pressure gauge to the exhaust system. Use a gauge that reads up to 8 to 10 psi and is calibrated in 1/2 inch increments. Or, use a metric pressure gauge calibrated in kilo-Pascals (kPa). One psi equals 6.895 kPa.

Google is your friend.

Rest of the article can be found at:

http://www.aa1car.com/library/converter.htmp

Good luck.

Easiest way to check is to use a thermometer:

http://isswww.co.uk/fluke-62-max-plu...Fcgp0wodNKsMVA

Post CAT temperature should be much higher, indicating the catalyst is working. Simple and effective and takes seconds and you don't even have to jack up the car...unless you can't get your arm underneath.

Thanks for that info...very helpful I have ordered an infra red thermometer and will report back next week.

http://www.youtube.com/watch?v=TjPL4D9Mdck

Those infra red thermometers go for buttons on eBay, although not sure if quality or upper temperature limit is up to the job

You need one that can read up to 600*C.

T5's run bloody hot. Drove mine for the first time for weeks the other day, went up the road and back again just gently breaking in some brake discs. The engine bay was roasting when I got back.

Is this hotter than 'normal'?

The first thing I'd be looking for is a split boost hose, it will cost you nothing to have a good look. Blowing open at 3K revs would feel like hitting a wall. As the ECU tries to adapt to the huge air loss it will run like a bag of ££££. If you find a split, replace the pipe and pull the ECU to reset adaption.

Quote:

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Originally Posted by Redbrick

T5's run bloody hot. Drove mine for the first time for weeks the other day, went up the road and back again just gently breaking in some brake discs. The engine bay was roasting when I got back.

Is this hotter than 'normal'?

The first thing I'd be looking for is a split boost hose, it will cost you nothing to have a good look. Blowing open at 3K revs would feel like hitting a wall. As the ECU tries to adapt to the huge air loss it will run like a bag of ££££. If you find a split, replace the pipe and pull the ECU to reset adaption.

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He means pull the ECU fuse! :)

I had a similar problem a long time ago. Ended up being an over-boost that the ECU was fighting against.

There was no simple symptom. It would boost fine, and every once in a while, it'd just drop off and show about 60%/75% on the dash gauge.

It could be an ignition misfire or "boost cut" due to an over boost. You should be able to feel the difference between the two and also see if it's over boosting by the boost gauge.

Replace the TCV.

Yep a new BCS solved my low boost issues... I'll see if I can find a link to that thread!

Here you go, for the low price it would certainly be my advice if all vacuum pipes etc are replaced: http://www.vpcuk.org/forums/showthre...4730-Which-BCS