aomdedude1

Why is my car faster when I unplug the MAF?
The car also is not doing so great on MPG. I will try and give official times with and without tomorrow. I am 65% sure this is not just my imagination. I unplugged the MAF today and took it for a short drive, and the car RIPS from 0-60 like a bat out of hell. With the MAF plugged in it acts like it is dragging an anchor!

I just recently started legally driving my car this past Saturday so I realy do not have much experience with the vehicle yet. Maybe this is normal? I was having issues with passing emissions prior to changing my O2 sensors. As I said, I will get "official" times for you guys tomorrow. Is there any way to diagnose this engine performance issue? Could this be caused by bad engine timing?

Here is a list of all the maintenance I have done before getting the car inspected:

- Timing Belt & pullies
- Water Pump
- Drive belts
- Plugs and wires
-Distributor caps and rotors
- Professional bench fuel injector cleaning and flow test by VAC motorsports
- Upper and lower intake removed and replaced with all new gaskets (to get to and repair the rear leaking water by pass joint)
- Air Filter
- Oil and OEM filter
- cooling sys. flush and OEM red coolant fill
- Power steering bypass valve replacement and PS sys. flush
- Front O2 Sensors
- Rear EGR bypass pipe replacement
- Coolant temp sensors
- ECU capacitor replacement (done by me as per LSCowboys guidelines.)
- Fuel Filter
... Probably more things that I can not remember at the moment.

Largefarva

Not normal, car should be slower with the maf unplugged since it would default to a rich condition to protect the engine. Time for a new maf I'd say.

LScowboyLS

very common for 94 and earlier AFM (MAF) to be bad, as well as the ones from the junkyard or ebay to be bad as well, because sometime in their life, some Beavis cleaned them with MAF cleaner, and you can only do that with 95 and newer

PS - I want to see photos of this ECU cap job, high resolution, before I will sign off on that part as being OK

aomdedude1

I stand by the motto, "pics or it didn't happen" 100%. Unfortunately, taking pics was not one of the things my brain thought of after completing the ECU repair. I guess I was in a hurry to see if it worked! The best I can do for you is a picture of my old caps that I removed.


I'm more than sure this does not help though! haha


I know that MAF is one hell of an expensive piece! I'll look up in the service manual for the test procedure and give it a good test. I've heard of people replacing the MAF with the same symptoms but not resolving the problem.

aomdedude1

DId a 0-60 with the MAF plugged in on the way to school. I used my phones stop watch and got 10.5 seconds with O/D off, trac off, and in power mode. I also got 0 wheel spin. I looked up the listed 0-60 time of the car and it is around 8.5 seconds. I know these times are by professionals who launch the car... but still, it seems a little slow.

Is this a normal time? I'll unplug the MAF and see the type of time I get on the way home.

Greg5OH

^that is disgustingly slow.

aomdedude1

Okay, that's along the lines of what I was thinking myself! I gotta figure this one out because it is annoying the crap out of me! What is a normal 0-60 time? Can anyone tell me what there 0-60 is?

My TRAC light came on today. Not the "Trac Off" light but the actual "TRAC" light in the middle of the speedometer. I have a feeling this might somehow be related because I've been having transmission issues where the car "floats" out of gear when I come to a stop light. It is especially prominent in reverse when backing out of my driveway in the morning. I'll pull the codes over the weekend and see what it says. My inclinations are that when I fixed my coolant bypass pipe and reinstalled the intake manifold, I may not have properly adjusted the cable that goes to the transmission. Maybe I simply need to adjust that. Hopefully it is as simple as that.

LScowboyLS

1994 LS400 should be 0-60 in 7.9 seconds, completely stock with premium fuel

aomdedude1

I have been using premium fuel since I have owned the car. (granted I have so far only filed the tank three times since buying it)

I just finished my very last drop of gas (orange fuel light was on) and barely made it to the local BP and filled her up. I had to stop half way because the damn Gas Tanker started pumping the station tanks before I could finish! (I don't like to fill my car when the tanker is filling to avoid getting the sediment at the bottom of the station tanks..) Anyway, I calculated my MPG since the last fill up (just this past Saturday!) and I am getting 11MPG!!!! That sounds hideous. Please don't tell me this is normal for the 94 ls400? Is it?

So now I have confirmed sluggish performance, and plausibly confirmed hideous gas millage. Something is DEFINITELY wrong here.

(ohh.. and as for the TRAC light, I have not yet checked the code but this morning before I left I took a few minutes and used a turkey baster to suck out nearly a full (small) bottle of brake fluid out. I replaced it with new fluid to the proper level (it was previously slightly over filled) and the TRAC light has since not come back on! I drove at least 30 miles today. The old fluid was quite nasty and starting to gel so I will be doing a proper FULL brake system bleed. I'm aware that I need to be real careful with the TRAC and ABS and not introduce air into the system.)

So no CEL's (other than the TRAC which has apparently been resolved). What could be my issue now? Any recommendations?
I guess I'll pull codes just to see if any are stored in memory.

p.s. : I'm not convinced that it is actually the MAF. I've heard people having this EXACT issue and replacing the MAF and NOT resolve the issue. I NEVER used any cleaner on the MAF of any kind, but I cannot speak for the previous owner.

LScowboyLS

something is definitely wrong, but don't worry, the gurus here at Club Lexus will get to the bottom of it, we always do!

and mileage on a properly working 94 should be about 21 around town, and about 25 on the Interstate

definitely pull the codes, using the procedure here

the next I would do is find a buddy with a properly running 93 or 94 LS400 and temporarily swap AFM's (MAFs) - they can be swapped in like 5 minutes - then see how each car runs with them swapped

swapping them temporarily is completely safe for both cars and will tell you a lot!

I am not saying it is for sure the AFM/MAF, but that is the first thing I would eliminate after the ECU

PS - I am still waiting on pics of that ECU interior! - need to verify you got all of the caps in the right places, and that polarities are correct etc.

As far as people replacing the AFM/MAF and it not fixing it - it is usual that the replacement is from ebay or junkyard and the replacement may have also been cleaned in its life - very very likely!

aomdedude1

Thank you LS.... and hey, I GUARANTEE you a photo of the ECU... but it might be a few days until I get around to that. I'll see if I can find anyone in my area to help me out who also owns an LS400 but that's gonna be a tough one. In my area for some reason I hardly EVER see any ls400's. (Philadelphia/Buck county area) If I do see them they are beat to car hell.... If I couldn't find someone on the forum in my area wouldn't it be funny if I walked up to a random LS400 and waited for the owner.... hey buddy, do you mind if we swap MAF's for a minute!? haha Maybe I can grab a real cheap junkyard MAF. I'll see what magic I can cook up.

First things first tho, I will go pull those codes before the weekend is out!

...and WOW at that gas millage. I wont stop until I can bask in great gas mileage like that! 21-25... wow. Not much worse than my 95 V6 accord.

LScowboyLS

another common cause of this type of issue is jumped time, but perhaps just a single tooth and on perhaps just a single cam

if you just did the timing belt, how confident are you that it is done correctly?

also, have you replaced the Engine Coolant Temperature Sensor using the genuine Toyota part?

aomdedude1

I am on board with thinking that the timing off. When I did the timing belt I used some Berryman B-12 Chemtool to clean all the valves (since I also have the intake off) by pouring it onto the valves that were 100% closed and letting it soak. Then I used a rag to sopp up the mess. I worked like a charm and the valves just completely shined! I did this for EVERY pair of valves by rotating the cam shaft.

So in other words, the timing is suspect. I could have it off by 180deg on one of the cams by mistake (is it even possible to be 180deg off and still have the lines line up??) . Would this produce similar results? If this was the case, I would expect to have massive a misfire.... which I do not.

With that said, I am 98.7% sure that my markings on the cams and crank are lined up because I checked and triple then quadruple checked this before finishing the timing job.

Is there any easy way of checking the timing other than looking at the marks on the cams and crank?

LScowboyLS

No, and not only that, you also have to verify the crank is at TDC, not just the 0 degree mark - which means cylinder #1 (front cylinder, driver's side) better hold pressure, showing you are on the compression stroke, rather than a revolution off and on the exhaust stroke! (both valves closed = holds air pressure vs. exhaust valve open = doesn't hold pressure)

also mark sure the two marks that you are aligning are cam pulley and cam backing plate marks, if you are just aligning the mark on the belt to just one or the other of those, that's not enough - if you count the timing belt itself's mark, then 3 marks must align on each cam

aomdedude1

Okay guys, here is what happened today. I feel pretty stupid for this but I think I may have finally found the source of my problems. I drove 70 miles today and got home around 4:45pm. I decided to take 2 seconds to check my trans fluid. .... it was so low it wasn't even registering on the dip stick! So I ran to the Toyota dealer before they closed at 6pm to pick up 2 quarts of type 4 atf. It took BOTH quarts!!! Wow!

So here is what happened. When I did my timing belt I took out the radiator to get easier access to my crack shaft bolt. When you take out the radiator you have to disconnect the trans lines that go to the radiator. That is how I lost so much fluid! I heard you should only loose about a half of a quart from disconnecting the lines but it was disconnected and dripping for at least a week. It might even of been low to begin with. Well I did this job over the course of 2 months last summer so I forgot to refill the trans when I was done!!

I also decided to take 2 seconds today and took of the TRAC cover (the plastic trim that covers the throttle cables.) Guess what? There was a significant amount of slack on the end of ALL the cables! Both the throttle, trans, and cruise cables!! I took the time to tighten them up and take away any slack then went for a test ride.

0-60 is now 8.33 seconds! MUCH better!
I can finally sleep easy now!

Thank you for all the help everyone. Moral of the story is double check your work especially if you do the project over the course of multiple weeks. It's easy to forget the simple things. It just amazes me how stupidly simple this stuff was. I feel like it is finally safe to say that I got a SMOKING deal on this car for the purchase price of 1000$ (it had a coolant leak I fixed)

Woo hoo!!

As far as unplugging the MAF making the car faster.... I don't know why.. this may have been placebo or just a fluke..