lorenolson888

Hi All,

I have been trouble shutzen and figure that my rough running problem is probably not the plug wires.

I remember having to tug on one of the vacuum lines that leads to the little "distributor piece" (looks like a tarantula spider) when putting it all back together. I may have yanked it loose.

I just pulled it off and sucked on it and there is absolutely no resistance... I know that people use vacuum gauge hand pump thingys to diagnose these systems... which lead me to beleive that there should at least be some resistance to me sucking on it... The line in question that leads to the tarantula was caught between an intake runner and the filler neck so when I tugged on it I did not notice if it came loose or not... but my memory does remember that it was a bit funny feeling.

So I think that I am about to pull the intakes back off again.

Can someone confirm that the system should give some resistance when sucking on it with the car off???

Thanks all,

Loren Olson

ErnestSw

Start the car and see if you can feel some suction from the line in question. Block the line and see whether the idle changes. If it does, that line may be the problem. If nothing changes you've got another leak as well as that one.

lorenolson888

Hi,

I started the car and I did feel a little suction at that tube... so it is probably hooked up. Also plugging the hole did not have any effect. So do you suspect another vacuum leak at a different point? Like I mantioned there is no resistance to suction with the car off.

Would the leak most likely be in the circuit under my intake...

I know your car is a 91 so it may not have the same parts...


Thanks,

Loren Olson

ErnestSw

My car doesn't have the same parts, but vacuum is vacuum. If you can feel a vacuum at the end of the tube, whatever it's supposed to be activating is not connected and that MAY be the cause of your problem. The fact that you can feel a vacuum suggests that it may be the only leak. You really can't tell anything from the lack of resistance to suction.

Bill 86.5 928s

Hey Loren....I'm having problems with my 86.5 as well. Rough idle , hesitation all of the above. My question to you is this....you mention the distributor thing where was it located and if you had to dissassemble the intake did you have to remove all ? what all did you take apart?...tnx

lorenolson888

Hi guys,

Thanks for letting me know I am not all alone here. Most of the 928 locals are in tahoe....

I did some reading and it seems that the vacuum parts in question are hooked to the intake and the strength of the vacuum varies with intake vacuum... so it varies with engine speed. makes sense...

Yes the little rubber distribution piece is under all of the intakes and you pretty much have to have the throttle body and aire tube (big macaroni thing out to see it....

I read that putting a cap over the maf should provide a sealed system. so blowing into the line going to the distribution peice should show a tight seal... and point of leaking would show up... So thismaybe a good way to find a leak... Some have mentioned blowing smoke into it and seeing where it comes out... ormaybe spray with soapy water....

Luckily i kept the dust covers that came with my new MAF so I will try and use that... I will let you know if it works for me...

Oh yeah, One thred said that he used a bycycle tube cut it around the valve stem and then clamped it to the maf inlet. Then He simply pumped it up with a bicycle pump.... that pressurized the intake systems and found his leak.

LO

lorenolson888

Seems like with the system plugged at the MAF my oral vacuum tester detects very little resistance to my blowing. So it looks like I have a LEAK...

Time to take the intake off again I guess....

The Vacuum system for HVAC, Cruise, and heater valve had a disconnected hose... though i doubt it would cause the car to run bad.... Is this the case? Is this system separate from the vacuum controlled fuel system? That seems to be the consensus.

Also if someone who has tried the leak check technique by sealing the maf inlet could comment on how this went... I am going to give it one more try... I pulled off the vacuum line to the diaphram valve (leads to carbon canister) and with the MAF inlet sealed I detected no back pressure to my mouth pressure...

Thanks All,

Loren Olson

BrianG

There seem to be 2 or even 3 separate vacuum systems on the 86.5 car, as I recall. There's the "spider" that you refer to, and I believe that that one is "port timed" at the throttle body..... which means that the vacuum port is uncovered by the throttle blade so little vacuum is seen at idle. Then there's the larger vacuum port that comes off the left side intake plenum of the manifold, which feeds the power brake booster. And, unless this was purely a bad dream, there's a tap, taken from the brake booster circuit that feeds the vacuum reservoir for the cruise control ( and possibly one other function).

So, there are all of these possible suspects in the vacuum system. Plus, all of the manifold component's joints.

I use a windex bottle (atomizer) with paint thinner (Varsol) and carefully spray around the suspect area(s). If there's a leak, it'll suck in the thinner and the engine will speed up, notably. Varsol is not very volatile, so there's little (but NOT zero) chance of an unexpected ignition, and the engine speed increase is mild.

DO NOT USE GASOLINE