High BLM's are caused by??

[tta1401]

I have done searches already on this and I know a few causes but I was wondering if I could get more detailed causes. For example, instaed of an exhaust leak, you could say the crossover pipe to header connection or instead of vacuum leak, it would be the vauum block gasket being bad. Why I ask is that I have been chasing a high BLM problem (150-151 at idle). I have to be missing something. Checked the headers for cracks when I pulled them off (Poston headers), pulled the crossover off and back on what seems like a thousand times. I was certain it was a crossover leak but I am not so sure anymore.

One question I have is will the BLM's be high on a vacuum leak and on an exhust leak? To me a vacuum leak is unmetered air which would cause it to go lean and an exhaust leak would cause the O2 sensor to detect more oxygen in the exhaust. I would think only the exhaust leak would cause high BLM's. I think I just confused myself!

Like I said before, I have searched and found some things on high BLM causes. What I plan on doing this weekend is swap out MAF's, check my grounds again, vacuum lines. I sprayed carb cleaner on all vacuum line connections and did not hear the RPM's go up any. I heard that the RPM's going up might not happen and I have to watch the BLM's on the scanmaster when I do this. Anything else I should do? BTW, CC's are good on the O2 sensor. I hate asking questions that have been asked but I had to do it anyways.:redface:

 

[3.8L V-8 eater]

Well I'll say this. Last summer had a massive header leak 160 BLM's. Fixed the header problem gone. This summer had a high BLM of 143 not as bad, but the problem surfaced as a gasket leak at the plenum which to me would be the same as a vac leak. Replaced the gasket did nothing else and BLM's went to 124. I've heard of bolts coming loose on the plenum that have caused high BLM's due to the pressure the work loose.

 

[bmackinnon]

add old, dirty fuel injectors to the list of high blm causes.... I figured this out after YEARS of trying to solve my high blms....

 

[tta1401]

add old, dirty fuel injectors to the list of high blm causes.... I figured this out after YEARS of trying to solve my high blms....

I went with that route 2 months ago thinking it was a sticky injector. Sent them off and they came back good. Still same problem though. On my old T, I had the plenum gasket blow out. Replaced it and BLM's came down to normal. I am going to check my vacuum block. I have had that off a couple of times and need to check if its warped (found that somewhere in a post).

 

[Roc87]

High BLMs, ECM adding extra fuel can be caused by clogged/dirty fuel filter, bad injectors, leaking injector, fuel pump on its way out, bad O2 sensor, exhaust leak, intake (vacuum leak) or a even a bad MAF.

 

[JimP]

All the suggestions above are good,

also check your baseline fuel pressure, if it is low the BLM's will rise in order to compensate by adding fuel.

 

[headstrong3157]

Another problem that can cause BLM issues are leaky throttle shaft seals. After replacing all the vacuum lines the BLMs weren't pegged out anymore but still weren't where they were supposed to be. Sent the throttle body off to Steve Monroe and had him put new seals in it and presto the BLMs were back down to where they are supposed to be.

 

[Chuck Leeper]

EGR leaking?
Maybe, it's time for a smoke test....
Have you put a vac gauge on the engine?

 

[Turbo6Smackdown]

High BLMs, ECM adding extra fuel can be caused by clogged/dirty fuel filter, bad injectors, leaking injector, fuel pump on its way out, bad O2 sensor, exhaust leak, intake (vacuum leak) or a even a bad MAF.

If this is true, you'd have a lean condition. Wouldn't you then, have KR as well? Is it possible to have high blm's without kr?

 

[forcedfedv6]

+10 or -10 on the blm's at idle is within specs, it will never be 128 at all times..

 

[Roc87]

If this is true, you'd have a lean condition. Wouldn't you then, have KR as well? Is it possible to have high blm's without kr?

The ecm sees a lean condition and is dumping extra fuel in to compensate. In my elcamino the BLMs are maxed and it's down to 12mpg highway Too many intake gaskets with an L98 So what I had listed is things that I've tried to correct, forgot to mention the EGR, haven't tried that one yet, but in my case on the L98 it's a TPI runner vacuum leak. It does seem like the GN would have KR for the lean condition, guess it just depends on how much extra fuel the ecm is ordering.

 

[tta1401]

All good suggestions! I have not yet done a vacuum leak test. I need to read up on how to do it (how does the smoke test work?). I did replace the EGR gasket. I checked the vacuum block and its good. Baseline FP is at 42-43psi. Fuel flter has been replaced within the last 1500 miles. Fule pressure is pretty new; fuel pressure goes up 1lb for every lb of boost. O2 sensor crosscounts reading good. MAF I still need to check but last time on a turbo link run, it read 255 @WOT. I still think its the crossover. Everytime I have taken it off and put it back on, it just doesn't look like it matches up very well on one side. I got a bottle of the liquid copper sealant I think I am going to use. I have the car in the air and I am going to pull it back off try and seal it better. I will loook for carbon tracks again. Is there another way of checking leaks at the crossover pipe? BTW, I was hitting 160/BLM# testing this weekend.