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Drfatz

From High MAP to Low MAP and Rich to Lean

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I thought I had this problem all figured out! For months I have been chasing low vacuum in my intake manifold. I took the car to two different "specialists" who both looked over the car and couldn't find anything wrong. Finally last night I decided to check the timing again, even though both "professionals" said the timing was right on. Well it wasn't and in fact each pulley was one tooth off. So I spent all of last night fixing the timing and fired her up. Well she runs a lot better now, but my MAP went from 0.7 at idle before I fixed the timing to 0.33 at idle <_< She was running rich before I fixed the timing and now she is running to lean. I made sure to set the FPR to ~45 psi with the vacuum line off. At idle I noticed my MAP reading to be around 0.33 which is much to low and I get a trouble code stating the MAP voltage is wrong. Finally, when I drive the car I notice as soon as I touch the throttle the engine almost dies before is begins to rev and if I rev it up and then let off I get lots of loud backfires and pops from the exhaust. I am completely perplexed as my problem seems to have gone 180 degrees. I went from to rich with high MAP to, to lean with low MAP! I am totally stumped. Why is my MAP so low!?!?!?!?!?

Just to let everyone know all of the manifold lines are hooked up properly with new fittings and silicon lines, I have brand new sensors, my compression is 155-160 across the board. I even went as far as to recheck the valve shims and they are all right within spec.

Finally, I attached a freescan of me driving down the street.

:):P<_<

run_lean.txt

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Graham - as a non-mechanic can I suggest you 'reboot' the ECU (if you haven't already). If it was leaning the mixture before and hasn't been reset by a power disconnect, it may just be confused?


Proud recipient of the LEF 'Car of the Month Award' February 2008

"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming: "Wow, what a ride!!"

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Graham - as a non-mechanic can I suggest you 'reboot' the ECU (if you haven't already). If it was leaning the mixture before and hasn't been reset by a power disconnect, it may just be confused?

As a force of habit whenever I make any major change to the car I always reset the ECU so that it can start fresh. I have a feeling that the throttle bodies may be closed to much since I was chasing a vacuum problem before. I am going to see about opening up the minimum air bleed screw to crack open the TBs a little more at idle.

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See what I mean - you've lost me already... that's why I limit my maintenance to plugs and filters, and pushing buttons marked 'reset' occasionally!

Good luck!

Edited by islandbloke

Proud recipient of the LEF 'Car of the Month Award' February 2008

"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming: "Wow, what a ride!!"

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My SE and my friends X180-R have a MAP ~.33-.37 at idle... (we are at 5200-8300ft though)

Comparing your file to an old one from the X180-R, and to an old one of mine with a broken chargecooler, it looks pretty much the same, though your O2 is a little lower than the X180-R and waaay lower than my SE.

Your IAC is a little high for idle at 54, should be 20-40.


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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My SE and my friends X180-R have a MAP ~.33-.37 at idle... (we are at 5200-8300ft though)

Comparing your file to an old one from the X180-R, and to an old one of mine with a broken chargecooler, it looks pretty much the same, though your O2 is a little lower than the X180-R and waaay lower than my SE.

Your IAC is a little high for idle at 54, should be 20-40.

Interesting that you say the file looks a lot like the X180-R.

The car is running very lean though which I attribute to the very low MAP sensor reading. When I tried opening up the throttle butterflies a little the RPMS went up, but the MAP dropped. Its almost as if the car is pulling so much vacuum now the car can't deal with it. I did take the head to a shop and have all the valves reseated along with a multiangle valve job done. I am wondering if its possible that the car is just running with higher tolerances then it did from the factory. Do you guys think its a throttle body problem (they had been tampered with) or do you think the O2 sensor is hosed? Or possibly both?

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Just a quick update, I managed to get the IAC and TPS to be right within spec at idle. I will say that she idles beautifully, but as soon as I touch that throttle she runs lean. My question is what causes the engine to pull to much vacuum? I tested my map sensor using a vacuum gauge and checked its output voltage using freescan and it is exactly within spec. I can understand not pulling enough vacuum (my previous problem) but now pulling TO much makes no sense to me. If I increase the throttle body opening it doesn't really help at all the MAP goes up a small amount, but then the idle starts to climb and the IAC can't control it anymore. If anyone has any clue I would appreciate the input.

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I've had stalling, when cold, whin my IAC is above 40 like yours.

Get your car up to full warm temp, ~82C

leave it idle, don't touch the throttle the whole time.

Using freescan check your IAC counts, should be between 20-40 when fully warm at idle.

if not, slowly and carefully adjust your minimum air rate bleed screw on the butterlies (NOT the butterfly balance adjuster bolt) while watching your IAC counts in freescan. It is very sensitive, turn the screwdriver very small amounts at a time and wait to see the IAC counts stabilize.

This assumes you have no other air leaks, and your butterlies are balanced.

I have also see the car stall when you touch the throttle, when a bad MAP was installed. In this case it was a 3Bar MAP, and the car would run and idle, and rev, but could not have any load at all without stumbling and stalling.


Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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Thanks travis for you input. I have my IAC at around 22 now. There are two issues one is when I first hit the throttle she stumbles a little and when I come off the throttle and come to a stop she drops in Rpm bit before returning to normal. Also she backfires like crazy when I let off the throttle, but I do have a 3" exhaust with a big turbo and race cat. Does backfiring damage your turbo?

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Graham,

that's pretty normal for a free flowing system, I just built a 3 1/2" system and pops and backfires on Decel, it's just air and hot unburned fuel igniting downstream. The ecm may need to really learn the setup, did you take a decent long highway drive to let the ecm calibrate? Also, how old is your fuel?

Artie


89 White Esprit SE

...a few little upgrades....

93 RX7.....Silverstone

....slightly modded...Muahaha...

New Addition:

1990 300ZX TT......Hmmm

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Graham,

that's pretty normal for a free flowing system, I just built a 3 1/2" system and pops and backfires on Decel, it's just air and hot unburned fuel igniting downstream. The ecm may need to really learn the setup, did you take a decent long highway drive to let the ecm calibrate? Also, how old is your fuel?

Artie

Cheers Art, my fuel is brand new and I have yet to really drive the car seeing as its not yet registered :) My biggest concern before I move forward with the engine tuning and driving around is the MAP sensor. I have used a vacuum gauge and checked the output voltage of my MAP and it is exaclty in Lotus spec. Thus it seems at idle when the car is warm my MAP is around 0.33-0.35 which seems really low. In fact the ECM gives me a trouble code saying the MAP voltage is to low. Is it possible that with all of the rebuilding the car just has a much stronger vacuum then a "normal" factory engine?

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Hi,

If I were you, I would thoroughly check ALL the piping/hoses once again ... Maybe you connected the vacuum circuit (= the REAL vacuum one which is driven by the vacuum pump !!!) somewhere to the Manifold Air Pressure system by mistake.

This can very easily happen in the area where the wastegate-solenoid and the two other solenoids (= T-connected to the REAL vacuum system). If you managed to bridge the two systems somwhere you will see too low MAP-pressure and also too low fuel pressure, because the fuel-pressure regulator also is connected to the MAP-system.

Cheers

Marcus

Edited by Paula&Marcus

Marcus

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Thanks Marcus for the input. I know the manifold lines like the back of my hand and I am 100% sure the MAP sensor is hooked up properly. In fact it is hooked up now with its own line going directly into the manifold so there is no chance for leaks or improper plumbing.

Edited by Drfatz

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And what about the other three connections on the manifold rail ???

There are actually four ports: Front, Rear and one side tap for the fuel-pressure-regulator and the breather valve connection

Cheers

Marcus

Thanks Marcus for the input. I know the manifold lines like the back of my hand and I am 100% sure the MAP sensor is hooked up properly. In fact it is hooked up now with its own line going directly into the manifold so there is no chance for leaks or improper plumbing.

Marcus

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Graham,

Sorry to hear you haven't been able to resolve this yet.

Out of curiosity, what is your fuel pressure with ignition on and engine off, engine at idle, and engine when revved?


1995 S4s

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Graham,

Sorry to hear you haven't been able to resolve this yet.

Out of curiosity, what is your fuel pressure with ignition on and engine off, engine at idle, and engine when revved?

I know all of my manifold ports are hooked up correctly. My fuel pressure at idle is around 40-42 psi, but it is adjustable so I can make it anything. It seems though that increasing the fuel pressure even up to around 50 at idle does not help my situation much. I am wondering if perhaps I should invest in a set of adjustable cam pulleys to really fine tune the timing. Also I am currently in the middle of installing a wideband O2 sensor so that I can really tell what the engine is doing.

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