Fault Diagnosis

Hello,

Car is a 1982 244 Turbo (kjet).

Over the last couple of days I have installed:
- Do88 intercooler
- new silicone couplers
- Oil catch can (generic) routed from PCV to catch to intake
- Replaced intake manifold (mahle gasket). Did have an issue with one stud.
- New o2 sensor

Took the car for a 5 minute drive today, wanted to ensure everything was well, but it wasn't.

On hard boost and when changing gear the exhaust pops and backfires - which is kinda cool but never done that before. Also, the temperature is up, its running hotter than normal, and its idling at 1500rpm instead of 900rpm.

I am assuming that the inlet manifold is not properly installed? Air is getting in? Would that account for increased temperature though? I torqued the bolts to 15lbft. Only one at the very end had an issue.

Any thoughts?

I'd suggest you do have some type of intake air leak if the idle is that high. It could also be the idle switch is now out of adjustment or failed so the idle control system doesn't know the throttle plate is closed. You can also have vacuum leaks from the injector oring seals. There are two on each injector. A thin oring and a thicker small donut.

Under full boost popping and backfiring can be caused by spark blowout. This could be from plugs with too large of a gap, or a weak spark from worn components. Use .028" plug gap which you can reduce if you know the rest of the system is up to snuff.

With the change of a better intercooler. It would be a good idea to have the fuel mixture checked to make sure it is correct and that you get enrichment under boost from the lambda control system.

I will check the inlet for leaks - like you said, its likely cause. I checked the plug gaps before I drove - all good.

Car was running fine before the changes. I don't suspect injector seals. They are pretty new, and like I said, these issues only occurred when I made the changes I did.

I have a wide-band so will make the appropriate adjustments to fuel.

May try and tighten up the bolts on the manifold and see of that helps, otherwise I guess I am purchasing a new gasket and starting over UGH!

You can spray around with brake cleaner and listen for a change in idle.

At the shop, we use an $moke machine.

Yes, I will spray around and look for leaks.

I should have also said that it didnt idle high at startup, it was only after I drove it for 5-10 mins that it happened.

I wasn't that keen on the mahle gasket when i received it, I much prefer the volvo gasket - may order that and replace.

update, found the issue! I checked the o2 sensor and it was loose! Not sure how i missed that or why i didn't tighten properly.

Anyway, tightened it up and the idle is now back to 900rpm.

Shame that I lost that popping sound at high revs...my 911 makes all sorts of loud popping noises when in "sport" mode, but the volvo sounded more genuine..

Glad you got that sorted out. I used to own an early 65 911 and a couple of 356 coupes many moons ago. I miss such fun cars.

dl242gt said:

Glad you got that sorted out. I used to own an early 65 911 and a couple of 356 coupes many moons ago. I miss such fun cars.

Click to expand...

And then the problem struck again this evening. I tightened the inlet manifold - went down to 1100rpm.

Ordered a genuine Volvo gasket, will take more care fitting it this time..

Seems to only happen when the car is driven for a couple of miles. Super annoying..

356 coupe - NICE car!