95 LQ1 MAP sensor?

[BlutRoyale93]

Hey all, New to forum and not 100% sure how this "Posting" business works, but here goes.

Does anybody know why my 95 LQ1 GP does not have a MAP sensor?

May sound like a total noob question but I've seen several images of an LQ1 intake diagram and they all show MAP.

[digitaloutsider]

Where, exactly, are you looking for it?

[Imp558]

See the black box towards the front with that green plug?

[BlutRoyale93]

Not sure how well the image comes out but the diagram shows a MAP being located here.

I didn't specify the details of the car, apologies 1995 Grand Prix LQ1.

[Imp558]

On the front of the engine

[Padgett]

Is apparently a MAP, guess a MAF in that location would not make sense.

 

Edited March 18, 2016 by Padgett

[Schurkey]

Not sure how well the image comes out but the diagram shows a MAP being located here.

I didn't specify the details of the car, apologies 1995 Grand Prix LQ1.

You have a '93-older diagram and a '95 vehicle.  That diagram shows EXACTLY where the MAP is on my '92 and '93 LQ1s.

 

(Edited to say '93-older instead of the previous " '94-older".  Thanks for the correction, Nas Escobar)

[BlutRoyale93]

Only reason I ask is because I went into my nearest O'Reilly Auto Parts and they misheard me when I asked for a replacement MAF and brought out a MAP.

I told them my year, model, make and engine and their system brought up a MAP, so I figured I should have one on the engine already. I even go onto the O'Reilly site and it shows a MAP.

It just confuses me as to why they make a MAP for my year and engine but I don't have one currently existing.

If anyone has any pointers or explanations I'd appreciate it.

[Nas Escobar]

1991-1993 LQ1's have a MAP sensor. 1994-1997 LQ1's have a MAF sensor. The MAP is located on the accessory pulley side (where the serpentine belt goes) of the engine on the top side of the intake plenum.

 

Your 95 Grand Prix won't have a MAP because it has a MAF where the air filter box is.

 

Not sure why O'Reilly's is giving you a MAP but Advance Auto Parts and Auto Zone both have MAFs listed for 94-97.

 

This is the part number at Advance's website. It is Reman, but should be available new somewhere. Here you go. 74-8309

[Padgett]

Seek and ye shall find (just need to persevere)

 

 

 

 

Edited March 18, 2016 by Padgett

[Nas Escobar]

That's the rear of your engine. The MAF is on the front, Where the MAP used to go on 91-93 is simply a vacuum line for 94 and 95. Can't confirm on 96 and 97 since I don't own an OBD2 LQ1

[Padgett]

Fixed it.

[Imp558]

That's uncommon, usually an engine will have a MAP even when they have a MAF.

[Padgett]

My Reattae have MAF sensors (ED21) but no MAP

 

 

 

[Imp558]

Usually

[BlutRoyale93]

Appreciate the responses.

I've replaced my MAF and figured I would replace the MAP as well but since I'm not equipped with one I won't worry about it.

 

On a different subject, what do you think would cause a fuel pump to make a groaning/grumbling/grinding noise when tank is at 1/4? This car is having a very irritating issue(s) that even a shop can't figure out. Figure I replace the small stuff that needs replacing anyway and see where I go from there.

[ron350]

BlutRoyale93 your 95 should have a MAP (Manifold Absolute Pressure Sensor) mounted on the throttle body adaptor just past the throttle body.

 

The MAF (Mass Air Flow) is mounted before the throttle body and measures air flow.The MAP (Manifold Absolute Pressure Sensor) is mounted on the other side of the TB and monitors manifold vacuum.

 

Why not post a picture of your motor in that area?

[55trucker]

BlutRoyale93 your 95 should have a MAP (Manifold Absolute Pressure Sensor) mounted on the throttle body adaptor just past the throttle body.

 

That arrangement only applies to the 96-97 engines which have a unique intake snorkel and are OBDII, the 94-95 engines which are OBDI.5 did not make use of the MAP.

[Padgett]

GM got into car computers in 1981 (CCC) and by 1988 had the second generation (P4) in most cars.  That said GM had a habit of keeping something that worked on older engines until forced into something new. The LQ1 is a good example of the latter with a high(er) speed ALDL but my 93 still has a single ring crank sensor while my 88 3800 has the dual ring. This is because the programming that worked in the 1985 2.8 still was usable in the 1993 LQ1 while the 3800 LN3 was a major redesign.

 

Then there is the MAP vs MAF war. For critical applications MAF (Mass Air Flow) is best. It tells you exactly how much air is flowing into the engine. With some manipulation (must also know the RPM, air temperature, and flow characteristics of the throttle body/air box MAP can calculate the air flow. Given the air flow and TPS, the computer can get a rough idea of the mixture (injector pulse width) required. The O2 sensor (heated is best) can dial it in the rest of the way.

 

So the MAF is more accurate but is also more expensive. MAP takes more inputs and is not quite as accurate but is much less expensive. For GM when the shift was made from the slow CCC system to the much faster P4s, there was enough computing power for MAP though MAF is still more accurate.

 

Meanwhile all of this is mainly to be able to generate MPG at cruise, once you pass about a 50% throttle opening you go into PE (Power Enrichment) and the main drive is to get enough fuel into the engine and not best MPG. In other words, when you stomp it at 60 mph the engine configuration goes from 30+ mpg to about 4. Here the MAF introduces a very small but noticeable drop in peak air flow that a MAP does not. At 4500 rpm this is barely noticeable. At 6500 weeeel.. This is why a L27 throttle body is much larger than a LN3 and the MAF peak was bumped from 170 gps to about 250.

 

A good tuner can look at the program in use and tell you a lot about the engine. Can say you do not want to use a NA map with a boosted engine (can drop a L67 supercharger on a LN3 but if you don't richen the maps A Lot, you will burn pistons (don't ask)).

Edited March 19, 2016 by Padgett

[Galaxie500XL]

There's no MAP on my TPI Camaro, either...but later cars abandoned MAF sensors, and went to speed density.

[Schurkey]

GM got into car computers in 1981 (CCC) and by 1988 had the second generation (P4) in most cars. 

I thought the faster computer started in '86.  Am I wrong?  Or was it phased-in over several model years?

 

1991-1993 LQ1's have a MAP sensor. 1994-1997 LQ1's have a MAF sensor.

I corrected my post.  Thanks.

 

On a different subject, what do you think would cause a fuel pump to make a groaning/grumbling/grinding noise when tank is at 1/4? This car is having a very irritating issue(s) that even a shop can't figure out. Figure I replace the small stuff that needs replacing anyway and see where I go from there.

First Guess:  Ruptured hose or damper between fuel pump and hanger assembly.  You don't hear the spraying fuel when the hose or damper is submerged, but when the fuel level is low enough, the fuel sprays on to something that causes a noise.

 

You'd have to drop the tank to find out.  Not a bad idea if you are unsure of the condition of the pump and pump "sock"; and the wiring harnes INSIDE the tank is a known trouble area due to corrosion.  A new pump, sock, and harness might be had for ~ $100.

[Padgett]

In-tank fuel pump usually fails around 100k miles, less if you consistently run below 1/4 tank. I keep a spare on hand because I knew it would be needed. After a bad experience with a cheap one, I only buy AC Delco.

[94 olds vert]

I run my tanks till they are dry. I'm looking forward to replacing the pump in my GTP. It's the original pump, as far as I know. I don't have a service record of it being replaced.

[BlutRoyale93]

It doesn't show symptoms of a failing fuel pump (that I know of) but it has consistent hot starting issues.

Mechanics say everything is "Performing as it should", but I seriously doubt bucking and jerking whenever I merge onto the highway is normal.

Not to mention 11.4mpg and stumbling on acceleration.

[Padgett]

Weak secondary ignition can act like that particularly when hot.