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High BLM's

950 Views 11 Replies 4 Participants Last post by  stevemon
Ok..looking to trace down a high BLM condition on two t-types.

This is whats been done and gone through.

Replaced all vacuum lines, PCV, O2, EGR and gasket, new plenum gaskets, new plugs, replaced MAF with known good one, swapped ECM's and swapped chips, ran MAF rite on throttle body. Engine appears to be really quiet on the drivers side and slight exhuast note on the passenger side. No sounds like a cracked header. Compression all cylinders came up to 170 PSI after 5 cycles.

Tested lines going to ball and cruise control with mity vac and they hold pressure. Cap'd the line to the power booster.

Whew...one car goes to 160 at idle..the other car has been hovering around 145-150. Adding fuel pressure doesnt change it.

Anyone have ideas???

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Almost forgot, no check valves.

IAC's adjusted to 30 at idle. TPS .42, MAF used was a known good GM one and an LT1 w/translator.

Plugs look ok. Not white.
what do the non-idle cells look like?

and...same chips in both? Translators?

As soon as the car starts moving they come down.

One car has a reds 50's the other has the extender. I swapped ecms and mafs from my own car and its pegs them. On my car the ecm and MAF read 127 at idle.

What specific cell's' do you want me to look at?

When cruising they come down to the 120's last I remember. So its not like they stay pegged at all ranges. Just at idle.

Engine runs for a couple seconds then stumbles when the ecm wants to make a correction. If you reset the computer , car idles fine fro a couple minutes, then the blm's take off..sometimes 150, sometimes 155 other 145-150..typically 155-160.

Was thinking of making a chip with the upper BLM limit at 200 and see how high it will go??

Thanks Steve for responding.

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I'm still leaning toward and exhaust leak. Did you get a chance to try the top engine cleaner?
Is cell 15 high as well?
What are the dip switch and Maf setting in the Translator?
Just to through this out there... Intake manifold to heads leak, throttle body bushing leak?

I was asking about the cells to see if the "problem" went away once the blms moved out of cell zero and it seems that it does. TD says the normal range of a stock set up is 105-150. (extenders will be different)

If the integrators are still within range, then the blms are still correcting to stoch at this point. Have you looked at them?

What is the maf reading at zero?

Assume you used the proper Delco pcv?

I think Paul covered the bases vacuum leakwise. Throttle shaft and intake manifold gasket are the two potential points that many ignore. And the usual, vacuum block to plenum, plenum to intake, hoses/storage balls, etc.....

We're doing the top engine cleaner today and see???

I'll record the event on my direct scan and see whats happening with the cells.

Yes AC Delco PCV.

Whats funny is both cars have 62 MM throttle bodies. We havent changed them to a 58 mm and try?? If I find the problem, i'll report back.

<small>[ October 29, 2003, 11:52 AM: Message edited by: Razor ]</small>
Update from yesterday..crack in drivers side header. Top engine cleaner smoke led to the crack. Funny thing is you cant hear it. Probably becuase it sucking air in. :)

I'll repost if welding the header fixes it. yeah yeah I know..welding the header is a whole other topic..



<small>[ October 30, 2003, 08:10 AM: Message edited by: Razor ]</small>
Just be sure the header is bolted securely to a head or a heavy, FLAT, piece of metal so it cannot warp when welded. Some add a piece of metal as a gusset, or bridge, between 3 & 5 just above the repaired crack for additional strength.

Get a good welder. Heat the area about the weld for stress relief and let cool completely before removing it from the head or piece of metal.

Thanks Steve.. We are fortunate to have a really good welder in the area. He custom makes stainless steel headers/exhuast systems as well as complete turnkey circle track cars.

I hear ya on bolting to a head and letting it cool.

I'll post when done. I like following up to insure future searchers get help.
FWIW, my welder friend who is aircraft certified insists on doing them using an argon purge. Says 400 series steel is already some dirty stuff so purging out the air gives him a better chance of getting a good weld. The technique is to tape up all the openings and poke a hole for the argon hose and another for an exit. Never had one crack again. (so far)
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