993 flat spot

[Chris-mac]

I run a 993 with the varioram engine and now and again I get a flat spot when putting the power down, it's not all the time and if you try to get it to do it it doesn't.

It happens between 2k and 3k rpm and feels like the air is being restricted, I thought maybe the varioram was playing up but at low rpm the varioram isn't in effect. Tick over is also sometime a bit erratic, could there be a link??

Any help would be appreciated.

Regards Chris

[smudger911]

i'd start with plugs, wires/caps
MAF - loose, needs cleaning
crank sensor

[Orangecurry]

I'd start with the easy cheaper stuff. I wouldn't touch the MAF until last.

If it hasn't been done for a while, I'd clean the ICV (or ISV if you are american) regardless. Easy job, and is then eliminated from the snag list

Just to check the varioram action - is there a strong 'clack' from the engine bay when you turn the ignition 'on' but don't start the car?

Check the air filter (very unlikely that it is causing the issue, but easy to access - if dirty replace with Mahle LX 459) but I really really would not go anywhere near the MAF yet.

Then it gets time-consuming - it could well be a vacuum leak in the rubber/plastic pipe network. The age/collapsible F-shaped connector is well worth replacing if it is original - mine was flat as a pancake at 39k miles.

The probables after that are I agree wires/caps/rotor-arms/plugs - when were they last done? Although the wires manufactured for the cars in the 1990s probably last for 50 years, there are exceptions, or they may have been damaged.

If someone else did the plugs, they may have 'missed' doing the very difficult one, so that's a possible.

If someone else did the caps and rotor arms, they may have used cheap ones - apparently Bosch currently make the best replacements.

But I'd be looking at vacuum leaks before going off onto the expensive stuff - do a search on Rennlist for some good guides.

[AW10]

Throttle position sensor is another one to check.

[Chris-mac]

Thanks for your help guys, I'll start with the ICV.

Orangecurry - what is the f- shaped connector and where can it be found?

Regards Chris

[Orangecurry]

So when you do the ICV,

http://www.orangecurry.com/993/icv-clean/

... whilst you are in there look for this...

http://rennlist.com/forums/993-forum/411521-where-...

993 110 573 00



.....and see if has 'collapsed' - but even if it has, it may not be your issue - that could be anywhere in the vacuum system, if it isn't simply a jammed ICV.

Edited by Orangecurry on Saturday 16th April 20:59

[Chris-mac]

Would a jammed ICV give me a flat spot while powering on or just irregular tickover?

Thanks for the links btw

Edited by Chris-mac on Saturday 16th April 22:19

[Orangecurry]

Probably just the latter, but clean it anyway and look for the f-shaped connector, and the pipes in and out.

Do you get the 'clack' noise?

[Chris-mac]

Yes I am getting the clacking sound which is coming from what looks like air diaphragm with an arm off it, to the left hand side.

[Orangecurry]

Mileage on the car?

When were the plugs last done?

When were the caps/arms last done?

Any mods?

[Chris-mac]

The car has done 68k
The plugs were done at 64k in 2014
Not sure about the caps
The only mod I'm aware of is the air box which has the chrome trim and drilled side

[Chris-mac]

I've cleaned the ICV, it was almost jammed solid, so I've left it in a bath of brake cleaner for a couple of hours, the f- shaped connector does look a little flat, so I'm going to order another one just to be safe, when I pulled the pipes off it there was a rush of air so I guess there aren't any leaks, well not at least on pipes connected here.

When I get these bits done a road test is in order.

Thanks for your help OC

[Orangecurry]

Sounds like you don't have any vacuum problems.

The ICV should have a lovely spring-loaded inertia to it once it is clean and free-moving.

Do let us know how the test-drive goes.

I suppose it's possible a plug-lead was damaged or is loose/arcing after reassembly? That would explain the intermittent fault if it isn't the ICV.

[Chris-mac]

ICV refitted ( right bug*** to refit) took your advice on turning the hose clips.

Road test done, all seems well, ticking over perfect at 800rpm, good power delivery too. I just need to fit the f connector and run it for a while as the power loss was intermittent.

It could be in my head but it definitely seems smoother.

Thanks again

Chris

[Orangecurry]

No problem - let's hope you've fixed it.

If not, and the car is a keeper, I'd be tempted to book a day with Wayne at Chip Wizards - he will test every component as part of a live remap, and you'll have the best power delivery that your engine can provide.

[Chris-mac]

The flat spot has just got flatter, tickover is all over the place when cold, it stalls and the won't start as it gassing up, the fuel smells very rich, there's a lack of power when driving and sometimes when you power on it dies like it run out of fuel!!!

So it's now sat in my repairer under investigation.

Gutted!!

[Orangecurry]

Damn shame - sounds like whichever sensor it is has now gone completely. At least if it is no longer intermittent it should be easy for the mechanic.

[SRT Hellcat]

From memory these have twin distributors. It sounds like the drive belt has snapped between the two disi's so you are only firing one set of plugs

[Chris-mac]

SRT Hellcat said:

From memory these have twin distributors. It sounds like the drive belt has snapped between the two disi's so you are only firing one set of plugs

The fault isn't consistent, it ticks over fine when it's warm, if the drive belt had broken it would run rough even when it was warm.

I've got a feeling it's a sensor but I'm sure it will get sorted.

[Chris-mac]

It appears that the lamba sensors have failed, I'm not sure if lamba sensors deteriorate over time or whether another issue has caused this problem.

So the new sensors are fitted and the car will be ready for me to collect in a couple of days.