Vacuum Leak fixing.

[sergitin32]

Hello guys, long time no see...
Me still enjoying the anguish of a vacuum leak in my 240 DL 1983, B21A Canadian Volvo.

I just spent a bag of coins rebuilding my carb hoping this would fix the issues, but not really, its worst now since the carb is stock and before was regulated super rich... so now is so lean it would barely idle without the choke and it would stall as I engage the transmission.

I am coming here today to wonder about "normal values" for manifold vacuum or MAP, at idle for my car...
Yesterday I isolate pretty much all the system so the manifold gets the air only through the carb and if so the leak...
I obtained 1 inch HG as my idle MAP. That obviously s***ks. So I would like to have a curve with the "normal values" VS rpm or something like that to use while I try to fix this issue.

I also found an air inlet hose not so air tight, but thats before the carb and would only harm the vacuum amplifier "signal"or something; I wouldn't think it to have much impact on my idle MAP... isn't it? Any one knows what a leaky inlet hose can cause?

As well a bad spark plug cable was found, but thats an easy fix.
On the bright side compression was close to 180 in all the cylinders and my sparkies were in good conditions.

Thanks very much and hope you are having a ball.

Sergitin.

[sergitin32]

Hello I have got some more info in my research for an idle issue that I've always thought to be a vacuum leak.

I did recently change all my vacuum hoses for HD Ipd ones. The problem did not improve.

Today I did some vacuum test and these are the results: (copied from my email to my volvo group.)

Hi there guys, I repeated the test today after reading more about the procedure... I plugged the PCV pipe and closed the bypass idle screw in the manifold so vacuum is more real for the cranking only test, I didn't plugged the EGR for the cranking but I do not think this system works under 400 rpms. Cranking was around 250-300 rpms (new battery installed 2 months ago)

I could not get a video of the cranking test since I didn't have an assistant. But I can tell you the needle would be fast oscillating between +2 positive pressure and 7 vacuum readings... with only the cranking test... that cant be good, on the other side the compression test was nearly perfect last time, so compression is not affected and I do not think the valve timing is altered. Valves shouldn't be sticky or burnt since I did a valve job like 20k km from now and haven't use the car much, plus my spark plugs are always beautifully bronzed brown even colour.

Then in the Idle Test, made everything back to normal and tried to go as close as possible to normal idle so I was around 1100 rpm (bad thing is choke was open otherwise there is no way to keep it idling) vacuum readings were on the "kinda healthy" area, between 15 (some times 14) and 18"Hg oscillating but slowly kinda following the rpms. The reading I've been doing says this carb miss adjusting mixture can create this.

Videos at:





My readings also mention oscillating at low rpms could be a worn valve guides but I think this is not my case, since I believe this would create fast oscillating needle and mine was slowly following the rpms... Also when you increase the rpms to 2k the needle steadies at 21.5"Hg which is a good number. I also did the snap test on the throttle and the readings were correct: on acceleration fast lowing to 4"Hg then back to 20-21"Hg then on deceleration higher to 25-26"Hg and back to idle 15-18"Hg, before idle it would go a little lower and like hesitant... I know if I do this with a cold engine it would die right there.

Quick background: I couldn't pass the emission test. NOx were too high when driving and the Hydro-Carbons were high at idle, but when driving HC were OK, here the bad numbers:

Driving NOx(ppm): max allowed: 2093 ---- readings in my car: 2420

Idle HC(ppm): max allowed: 402 ---- readings in my car: 1112 (VERY HIGH)

I must say I need to pull the choke out to have the car running, this would make the HC to be higher obviously, but then what can I do?

Also CO were very low... so my combustion kinda sucks? allowed 2.5%, my readings 0.1%, average passing was 0.86%

sorry the long email... My insurance extension in order to fix this is expiring this month and emission test need to be taken in order to re apply for any further insurance... I dont really use the car that much, but I like it a lot and dont want to give up on it... much less now that I have my virgo rims and my IPd sport springs to be installed soon.

Please hit me back if you get any ideas, any at all.

Cheers.

Sergitin