Thread: Low Manifold vacume!

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Well I guess I will start at the beginning, I built a small block 350, to go into a 78 monty. Well that plan fell through and needed a motor for my S10 blazer. well its in, but it wont Idle The manifold vacume is only 15 kpi and my map sensor is telling the Ecm that it needs more fuel. The cam I have in is not saposed to cause a lopie idle but it does. I know I dont have any vacume leaks cause I checked that with a smoke machine.
The lobe seperation on the cam 110 and the lift is .458 at 284 deg. So as u can tell I dont know if I should advance or retard the cam timing. What kind of vacume should this cam produce?
Any info would be a big help.

What fuel injection system are you running? 78 Monte didn't have one, and S10's didn't have 350 V8s...more info needed as to what ECM is being used, etc.

Kpi? Inches of mercury? If that 14 is inches, that don't sound too low.

Lopey idle? Hmm, no vac line off, hooked up wrong, leaky vac brake booster?
Sure timing is on? firing order is right?

Is cam set up right (timed right?) Are the valves all set up right and even with eathother (none too tight or to loose?)

re-check the basics!!

STREETS.
the 350 in a blazer...what i was referring to was his comment about the ECM...Electronic Control Module for you points guys. Since the 78 didn't have one, and the S10 had a 4 or V6 he can't be using that one (or he may be....a problem right there!), what is he running? He says engine needs more fuel...well, that is the job of the ECM, isn't it? (need pictures? charts? graphs?)

"My MAP sensor is telling the ECM it needs more fuel" - not likley.
MAP - manifold absolute pressure sensor. It reads vacuum and load on engine. O2 sensor read rich/lean and THAT might tell the computer that more fuel is needed.

What he probably has is an out of range on the map sensor due to lopey idle or low vacuum....

been a while since i used a vac guage...correct me if i'm wonrg (i know you might hesitate, but don't) 18 is about max, 14 is normal and under 11 is low? I don't get into anything where ti sis an issue. On synchromizing bike carbs, vac between cyclinders matters, not absolute vac reading.

Tech,
Wasn't too sure. Played with an in=dash vac guage back in the late 70s, but then it was used for 'fuel efficiency' - before the E-Shift light was commonplace.

I know 9 is too low for vac brakes, and they sell vac pumps for cars that can't, umm, get it up to 16". Now you know i couldn't pass that up!

My lincoln (and some GM cars and diesels) use 'hydroboost'.

Driven a few original 50s cars with vac wipers and such. Don't drive up hill in the rain!

I had a pinhole in one for the brake booster feeder lines. it peed only at full lock, and onto the exhaust manifold, so the leak was hard to find. Eventually found it, then had to find the line. finally got it replaced this past spring. the brake pedal no longer sinks erratically (thought the MC was going bad). Now that things are as they should be - WOW what brakes! I don't want vac brakes no more!

Have had PS and manual steering. Prefer power on daily driver. Had a 72 charger with 400 and manual steering. Parking that would make a man out of ya! If i recall, 370 turns lock to lock, and it took 140 ft pounds of torque to turn the wheel.

Ok now that I have some more time to describe what is going on with my S10 blazer.
The Block is a 350, 40 over I have stock rods with K/B flat top pistons. The cam is a Lunati part # 638-00016lk Adv. Duration is 284deg Gross lift .458" at 110 lobe sep. At the time of perchase the sheet said Strong low to midrange torque. The heads are from World Products with 2.02 in and 1.6 exh with 64cc chamber I found out when I got them that they wher 305 heads, light casting.
The blazer is a 1990 4/4 I wanted to keep the Blazer Tbi for the drivabilty factor, so I went to my nabor hood junk yard and got an intake, dist, Ecm and Tbi with good injectors.
I also installed a aftermarket prom, to help out the Ecm. I have noticed that the motor runs best with 8' base timing, I dont know what the total advance is.
I do think that I might have a vacumme leak cause I did notice on the way home from the shop that it did surge at the stop sighn. I will double check for any vacumme leaks especialy a leaky intake cause I did have to scunt the 4 center holes to get the intake to fit the old heads. What I would like to know is how I can get more vacumme out of this cam wether it be by retarding the crank, or with that lobe seperation Im stuck. Cause to do a cam swap It would be easier to pull the motor back out than to get the cam out the front. Or can I supply an artificial vacumme sourse. Im kinda limited on room for a belt driven pump, but might be able to fine some room for a electric pump. Tommorow I will double check my valve lash and do a compression test, and if that all looks good then I will drop the exhaust and see how it runs, that should get the neighbors up so they can have something else to cry about
I will keep U all posted. Thanks for any help, and all the help.

If it dont Go chrome it !!!