blm's still pegged at 150

[irrompible]

The problem is only at idle. Any sort of throttle and they jump right to ~128, let off and they instantly go to 150. I'm pretty sure the problem is a vac leak. The only possible one I've found is near the back of the vac block itself. I found it by putting a piece of vac line to my ear and going around all the seals and gaskets. The carb cleaner trick didn't seem to pick it up, so I don't know how serious the leak is, but I'm assuming it's little. Would this cause the blm's to instantly go from 150 to 128 and back to 150 or would it take a bigger leak? Thanks for any help you guys can offer.

 

[MistaScott]

Best thing to do is invest in a MityVac at Autozone. They cost around $20 and can see whether lines are holding vacuum. Otherwise you will never quite be sure you have found all the leaks.

 

[irrompible]

I replaced the vac block gasket and now the BLM's hover around ~148 in idle. I'm still waiting for my AC Delco PCV valve to come in this friday. In the mean time I used the GM Top Engine Cleaner and noticed what may be a DS header crack. The smoke was not real noticable, but it was there. It's entirely possible that I could have dripped some down there and it was just burning off but I'll pull the header tomorrow to be sure.

 

[MistaScott]

For what it's worth, here is what caused my BLM problem at idle only:

1) Driver's side header leak (not much smoke either)
2) EGR valve leak (Top Engine came dripping out of the EGR valve)
3) Incorrect MAF sensor (did not meter air properly)

My theory on why the BLMs were only pegged at idle is that an improperly calibrated MAF has more effect at idle than at cruise because the idle MAF numbers are so small (4-6gps) as opposed to cruise numbers in the 100s or 200s. A calibration off by only a couple gps means a lot more at idle than at cruise.

 

[Cme2fly]

Definitly a Vacuum leak period... could be your plenum gasket, throttle body gasket , or vacuum block gasket. change them all, I think I payed 9.00 at the dealer for all the gaskets above. also, change all your vacuum lines, PCV ,and check valves if you already havent. BL can be a B**ch but remember these cars are get old and rubber tends to rot after time. Do a search on this topic, you will find a wealth of info...good luck

 

[irrompible]

Well I just finished taking my DS header off and it was cracked almost the whole way around. I had it welded and am going to put it back on tomorrow. I noticed there was no gasket on the header when I took it off. Is there a gasket or some kind of sealer that needs to go on when I reattach it, or is the metal to metal contact fine?

 

[d0n_3d]

Originally posted by irrompible
Well I just finished taking my DS header off and it was cracked almost the whole way around. I had it welded and am going to put it back on tomorrow. I noticed there was no gasket on the header when I took it off. Is there a gasket or some kind of sealer that needs to go on when I reattach it, or is the metal to metal contact fine?

you need to get a set of felpro header gaskets part # 1400...you can get them from advanced auto parts...something like $15 or something...no sealer...just install dry, guaranteed not to leak or your money back

actually i had a blm problem as well for 3 years...always pegged at 150 and i changed every part imaginable trying to fix it...STILL ran filthy rich...when i tore apart my motor over the winter i noticed black streaks coming off the exhaust ports on the heads and also on the mating surfaces of the factory headers...they used no gasket from the factory and over time it slightly warped causing the exhaust leaks...problem found...problem solved

 

[MistaScott]

Took mine off, welded, put it back on w/o gaskets. No leaks. Just my experience.

 

[irrompible]

So far I've changed the vac block gasket, had the DS header welded and put in an AC Delco PCV valve, check and changed all vac lines, use carb cleaner and top engine cleaner to look for any extra leaks... but my BLM's still climb to 150 at idle. I'm about to pull my hair out.

 

[MistaScott]

What is your MAF reading at idle? WOT?

 

[irrompible]

5 at idle, and the highest I saw was 205 at WOT. BLM at 142 at WOT. I'm starting to think it's a fuel deivery issue, thoughts on that?

 

[MistaScott]

Yes, I'd begin to suspect fuel at this point. First, get the idle fuel pressure reading at line off. Unfortunately, this is headed toward injectors...

Other things to look at also:

--Make sure your MAF is the correct AC Delco factory unit (connector at right angle to MAF cylinder).

--Change the o2 for good measure if it is old or non-Delco/Denso.

--Listen for a whistle at part throttle. If you hear it, you may have leaking throttle shaft seals.

--Intake plenum gasket, TB gasket, IAC gasket, EGR gasket are all worth a look. Depending on where they are leaking, the Top Engine Cleaner should seep out of the leak.

--Also, I don't know if you've tried putting gasket material over the vac block to block the vac lines and then reading BLMs. They should go down somewhat but still be pegged. That way you have completely eliminated the vac system.

Good Luck

 

[77tech9]

I have the same problem, but my numbers are 160 at idle.

They climb from 128 once closed loop kicks in it just slowly gets to 160 and stays.

I tryed blocking off the vac block and same numbers, checked all connections before TB, they all seem to be perfect.

I dont hear a vac leak anywhere and car runs fine. I have stock injectors that I changed, could those be the problem?

I havn't changed any of the plenum, tb, egr gaskets, etc.. Can I get those at just the parts store?

 

[77tech9]

Also, my MAF readings at idle are weird, sometimes as low as 3-4.

Is this because of my high altitude? I swapped maf and tryed putting maf directly on TB and still same readings.

My headers are poston and the leaks have all been fixed.

 

[Marc87GN]

I'm experiencing the same problem with BLM at 150 at idle and then it drops to 128 above 1,000 rpms. I have sprayed the engine down with carb cleaner 3 times and it would have definitely affected idle quality or O2 readings on turbolink if there was an exhaust leak. I sealed the exhaust leak on the driver side and passenger side. I'm running a heated o2 so that's not it. I'm guessing it's the MAF. It shows 3gps at idle with both screens missing. I was told these meters are very touchy about that and I ordered an LT1 MAF with translator.

 

[77tech9]

Once my TPS hits over .45 it corrects to 128.

 

[77tech9]

After driving around a few times today, the BLMs would get down to 130 sometimes after it was warm, then when driving for a few back up to 150-160 then back down sometimes.

Exhaust leak maybe? I have a crappy poston downpipe

 

[irrompible]

Originally posted by 77tech9
After driving around a few times today, the BLMs would get down to 130 sometimes after it was warm, then when driving for a few back up to 150-160 then back down sometimes.

Exhaust leak maybe? I have a crappy poston downpipe

I don't suspect the downpipe would have anything to do with it as it's after the O2 sensor.

I would check all gaskets and see what that turns up. I used a long piece of vac hose to do it. Just put one end to your ear and run the other around the gasket and you'll hear the air if there is a leak. I know you can get the EGR gasket at local part stores and I suspect the rest would be the same. Although I did have to order the vac block gasket from the local GM dealer because that was one I couldn't find anywhere else.

 

[buzzman]

Guys, I am not an expert on this but have been following the thread with some interest. My blm about 140 at hot idle. I did a little test tonite, I put the stock chip back in and......128.....then I put an old Hypertech Stage chip in and.......127. I then put my Reds 93 back in and 140. I know your chasing vacuum leaks but have you put a stock chip in and then checked blm? Just a thought.

 

[77tech9]

I'll have to try messing with the chips.

My gaskets are prob 18 years old so i'll change them anyways.