effect of new MAF on blm's

[turbobuickman]

This is a theory I concocted about what is happening with my car. The symptoms are an intake backfire only when I punch it (good cruising, good top end, but just one backfire in between if I dont ease onto it)

Suppose there is a possible vaccum leak somewhere and it might be causing the blm's to be higher than desireable, then the maf dies and is replaced with an LS1 with translator. The translator is set so that the engine idles as smooth as possible and now the blm's are right on but the car is still showing signs of a vaccum leak(s)...could the translator be compensating for the "pirate air" and making blms normal but only at idle?

Second, if the MAF is compensating for the pirate air at idle, could the transition between vaccum and boost be quick enough as to not allow the computer to adjust for the air lost out the vaccum leak, thus causing the mixture to be rich and causing an intake backfire?

Gotta figure this one out...

Kyle

 

[Dan Thompson]

The input to the Translator would never know there is a vacuum leak. The MAF does know and the switches don't know.

 

[turbobuickman]

so its not possible that the translator (having been set by a human to make the engine idle the smoothest) might be tricking the computer into thinking that the maf is measuring more air than it actually is and thus compensating for the air that gets in after the maf???

 

[Dan Thompson]

If the translator is set for the wrong MAF, then who knows what will happen.

If you happen to have a vacuum/boost gauge the idle vacuum in Park should be around 18#s and in Drive about 14#s.

Is there a hole in the intake between the MAF and turbo?

Might try www.fullthrottletech.com as they sell the Translator/Plus
and could help you out.

 

[Eric Stage I]

What are the other conditions, like boost level, alky on or off, O2's. You said the blm's were ok, but you think it still has a vac leak. What is it that's indicating a vac leak?

If you turn the boost way down, does it still do it?

Regards,
Eric

 

[Rickracer]

How's the ignition system?

Possibly a weak or shorting/shorted spark? about 10 years ago, I had a little Turbo Pontiac 2.0 drive me nuts for about a week with a similar problem. Turned out to be a weak coil. It only showed up under boost, so I never saw it, on the scope it looked perfect, but the 40KV (spec) coil was only able to put out about 24 KV. At 6~8 lbs of boost and up, it needed more than that.

 

[turbobuickman]

I think it still may have a vaccum leak just because that is a common cause of tip-in problems. Boost was at 22, turned it down to stockish and it might have lessened the intensity a bit but the backfire happens when the boost first comes on not at max boost... It isnt alky related because ive tried all different settings including off and still does it. O2 x-counts are active and when the sm records O2's its usually around 780. Id like to swap a coilpack and/or ign module with someone but dont have any friends in the area with a TB. Can I rule out coilpack since it still runs smooth and pulls hard up top? Might make the drive out to Cotton's one of these days.

 

[Robert Walton]

An intake backfire is the result of fuel too lean or timing is off. There could also be some cam timing problems too but your symptoms don't sound like that is an issue. Your BLM was off with the stock MAF. What is off ? Too high,above 128,means it's adding fuel. I think you could have " fooled " the computer into ignoring a vacuum leak with the Translator. I don't know for sure as I don't have one. Good luck.

 

[turbobuickman]

I was under the impression that too rich could also cause intake backfire, correct me if Im wrong... and yes the blm's were high...so I think its safe to conclude that the translator is just masking a vaccum leak. Guess how I'll be spending my spare time for the next few weeks

P.S. If timing was off, wouldnt the ill effects be just as noticeable if not magnified up top?

 

[Rickracer]

If it does it at tip-in and not max boost....

...just file that little tidbit in yer noggin. Sounds like a fuel related issue for sure. Is timing jumping around under acceleration?

 

[BJM]

Do you suffer any tip-in issues anywhere in your operating range? A severe lean tip-in problem could cause the backfire but I would not expect it only to happen when punching it.

A TPS with a dead spot up at higher voltages would cause a fueling hiccup while operating normally otherwise. Do you have a spare TPS?

 

[turbobuickman]

Rickracer--I dont know how timing could be jumping around under accelleration unless maybe the timing chain is stretched or sumthin. I know my fuel filter is really old and have been trying to get it off without ruining the lines for a while now, could this somehow be starving the engine ONLY at tip-in??? What about the stock injectors? I know they can supply enough fuel up top but can old injectors cause this?

BJM--The tps is set properly and I dont have a spare. Could I just verify that the voltage is linear by watching the sm and stepping on the pedal while the car is off? Maybe Ill try unplugging the TPS-TEC, most people think they are usless anyway.

 

[BJM]

Definitely try without the TPS-TEC thing. The nicest way to verify the TPS is to use an analogue volt meter and run the TPS up and down and watch for the needle to jerk around. The Scanmaster would only register a really big dead spot.

If your car runs at more than half throttle then the fuel filter won't be affecting tip-in. The fuel requirement is still quite small.

 

[turbobuickman]

I verified that the tps was from .44 to 4.6 and watched the readings climb on the sm and they were pretty regular up until around 3.0 then they jumped and pegged at 4.65. I think that is what the tec is supposed to do but it seems like it might screw sumthin up with that gigantic jump in tps. Then i unplugged the tec and the tps readings were way off, adjusted them back to .44 and 4.6 then took it for a spin. Throttle response seemed much better and the first few blasts were nice n smooth all the way up (o2s around 800-820, rich i know and kr 0.0). A couple times if I floored it as hard as i could from cruising at less than 30 it did still pop and stumble however. So removing the tec helped a lot but didnt cure the problem.
My sm readings are as follows: AF 05, LB 37, int 128, blm 128, iac 10pegged, cc very active. Any other ideas?