Restrictor for MAP sensor

[drews240]

I have been having bucking problems and someone suggested putting a restrictor in line with the MAP sensor tube. Has anyone tried this? what do you use. Some say a welding tip and a fuel filter.

 

Any help would be appreciated.

 

Thanks

 

Drew

 

Nissan 240Z race car with VQ Hybrid 3L with 350Z nismo top end.

[mobythevan]

My car would buck until I set decel fuel cut to 100%.

 

The restrictor sounds like more of a band aid fix that will cause slow MAP reaction times that could affect other areas of tuning. I think I would discuss it more and see if you can just adjust the megasquirt to fix the problem. Also let us know what the reasoning was behind using the restrictor, maybe it is a valid concern in your setup.

[z-ya]

No MAP restrictor should ever be required with MS. Moby is probably right about the decel fuel cut. Also check you acceleration enrichment settings.

[Clifton]

Have you logged the buck? I have a miss/quick surge that is from a " voltage spike" according to the log that spikes the pulse width to 32ms and causes a nasty buck. Others with the problem have had to run a noise filter on the flyback. This is a MS2, V3.

[eec564]

The restrictor idea was only for people with very large cams, as well as irregular and low vacume at idle. The idea being smooth out the changes (and at the same time make the map sensor less responsive through the entire range, while tuning and AE enrichment can be used to make up for much of it, it's still not perfect) in manifold pressure, averaging them out a bit.

 

Your bucking is most likely not caused by a poor (uneven, yet accurate) vacume signal going to the MAP sensor. You are most likely having a miss-fire, or megasquirt is missing an ignition event, and skipping injecting fuel once, or twice, or more. You didn't say how you were firing spark, or triggering megasquirt, so your exact set up may not be perfectly in line with what I said. An osciliscope on the post processed line (where the megasquirt cpu sees the trigger signal) should show you the even-ness of the ignition signal and if it's dropping any or seeing spikes. For the vast majority of people, an osciliscope is out of reach ($$$ and PITA technical know-how), so try other things first.

 

Also, keep a close eye on how long your injectors are firing, and if anything else is going on, such as AE, warm up enrichment, etc. You may want to try setting all values to 100%, except for your VE table, and spark table (if using megasquirt for timing) and see if it's still happening. Setting your spark table to all 10s (again, if using megasquirt for timing) may help eliminate one possibility.

 

If you can duplicate the problem while not moving, check the timing, fuel pressure, etc. If you have a wide-band O2, use that to log (at the highest sample rate) exactly what the fuel injectors are doing.

 

Good luck! Intermittant problems are a major pain, but they teach you a LOT when you DIY.

[Drax240z]

The restrictor idea can work. I found that when I had an excessively long vacuum line going to my map sensor (ie: high volume of air in the tube) that the restrictor sped up the response of the MAP sensor very noticeably, and smoothed things out. Since then, I've shortened up the line and relocated the MAP sensor which had the same effect.

[z-ya]

I have mounted ECUs on the tunnel between the seats, and have had no problems with MAP responsivness. If you are running a radical cam, you need to switch to Alpha-N mode. With a radical cam, you have verry little pressure range, so you don't have much control over fuel using the VE table and MAP sensor.

[woldson]

ok, would not a restricter slow respone? Also you would not get any more vacumme then what the engine is giving you?? With breaks you have a greater suface area to give you an increase on vacumme i believe due to hydralics?? Am i off base here or did i not read correctly:rolleyesg please advise.

[drews240]

MS2 V3 ... on a VQ30DE nissan engine running 350z heads

i isolated the problem to ~5000rpm , seems like the map sensor is going wild making the ms jump from table to table. The leaner table makes the car stumble and makes the driver unhappy and really frustrated

Now the solutions ? Run a restrictor+fuel filter on the map line ? Smothen the map signal in megatune ? Change the map sensor pickup ?(right now it's picking the signal on the small vacuum on the top of the plenum, it's located near cylinder 1 intake tube )

PS : The car was tuned on he dyno so the AFR IS RIGHT , the car is not in accel mode when the cuts appear and it is not because the accel mode goes off that it is leaning .

If anyone has a solution i'd be glad to hear it !

 

[drews240]

oooopppppssss!!!

[z-ya]

So, looking at the second plot from the top, the RPM is yellow, MAP is blue. What is red, injector pulse width? If so, the PW follows the MAP. This looks OK.

 

On the bottom plot, why is the TPSacc glitching? This would absolutely cause the engine to buck. From what I can see, the problem is not the MAP sensor, but the TPS or the wiring to the TPS. Are the TPS wires shielded? At 5000RPM, there may be noise coupling into the TPS circuit. Get some two wire sheilded cable, and run the +5 and TPS signal on the inner two wires, and connect the sheild to ground back at the MS. Do not ground the sheild at the TPS.

 

Another thing to check is the TPS. With an ohm meter connected between the middle terminal and either outer terminal move the throttle plate. You should see a very smooth change in resistance. If the resistance jumps at all, this is your problem. Try cleaning it with some TV tuner spray, or just buy a new one.

 

Let us know how you make out.

[Clifton]

Do you have an excel log?

 

This was taken from the Meagsquirt site.

 

"Don't worry about how long your MAP sensor vacuum hose is. Intuitively it seems that shorter should be better. However, a few people have done tests to see how bad the effect of a long hose was on vacuum signal propagation. With a ~100 foot (~30 meters) coil of rubber tubing in between the MegaSquirt and the engine, the result was that no delay was apparent. This was with about a 10 millisecond resolution clock. The reason for this is that air has so little inertia that it moves very quickly in response to a vacuum (this is how we fill the cylinders, after all!)."

[Guest 200sxBoY]

I don't see any TPS glitch anywhere

 

The problem is obvously not with the TPS , neither with the advance or fuel

 

If you see carefully the map goes crazy after a slight rpm decrease (probably caused by a missfire)

One thing leads to another the map goes crazy and the VE values follows which makes the situation even worse

 

We will try tomorrow to power up the ignition system,regap the plugs and check if the spark plug wires are still good and also use a restrictor

[z-ya]

If you look at the bottom most plot, the blue trace (TPSacc), you will see three glitches in the higher RPMs. Am I reading this wrong? It looks to me like glitches on the TPS signal. This is very common if the TPS signal is routed near spark plug wires and or other EMI sources.

[eec564]

Unless you test something and find out it's bad, you should try testing the system between each change. You'll feel better (and so will your wallet) if you make one change and everything works, rather then making 50 changes and it working, but not knowing what did it. Knowing what was wrong will be the key to reliability down the road.

 

-Eric

[drews240]

So, looking at the second plot from the top, the RPM is yellow, MAP is blue. What is red, injector pulse width? If so, the PW follows the MAP. This looks OK.

 

On the bottom plot, why is the TPSacc glitching? This would absolutely cause the engine to buck. From what I can see, the problem is not the MAP sensor, but the TPS or the wiring to the TPS. Are the TPS wires shielded? At 5000RPM, there may be noise coupling into the TPS circuit. Get some two wire sheilded cable, and run the +5 and TPS signal on the inner two wires, and connect the sheild to ground back at the MS. Do not ground the sheild at the TPS.

 

Another thing to check is the TPS. With an ohm meter connected between the middle terminal and either outer terminal move the throttle plate. You should see a very smooth change in resistance. If the resistance jumps at all, this is your problem. Try cleaning it with some TV tuner spray, or just buy a new one.

 

Let us know how you make out.

 

Well we took it to the Dyno the other night to see if we could address the issues, in a sequence we changed wires after soaking the set I had in salt water to check for arching we did a test and the cuts went away. So we changed the wires and the cuts were still there around 5000 RPM. So we then changed the Coil pack, still no change, decided to regap the plugs to a point to see if it is a wire and coil issue or a ignition module, sensor or wiring issue, We regapped the plugs rediculous to like 80 and it killed the power and moved the cuts to 4000RPM roughly so the two tuners said it is a electronic thing for sure, we then looked at the sending ring and jiggled it a bit to see if it was moving at all and it was slightly but it is like 1/2" thick it is not moving enough to effect anything?? is it? my question is, is the harmonic balance offset because of the press fit ring on the face of the crank pully and at heavy load it is just going crazy? we tested everything for noise (none) all the grounds are good. can I send someone my settings to look at and see if they are cool for this application?

 

Thanks

 

Drew

[z-ya]

Did you put a scope on the TPS signal wire? Again, is this wire sheilded from interference? I don't think it has anything to do with ignition except for the fact that the ignition energy is the agressor, and the TPS signal is the victim. When you have 40,000V+ noise running around sensitive 5V analog signals, the smaller of the two signals is bound to be interfered with.

[drews240]

Did you put a scope on the TPS signal wire? Again, is this wire sheilded from interference? I don't think it has anything to do with ignition except for the fact that the ignition energy is the agressor, and the TPS signal is the victim. When you have 40,000V+ noise running around sensitive 5V analog signals, the smaller of the two signals is bound to be interfered with.

 

I should have cleared this up before, in the graph the TPS dips are me letting off and back on the accelerator when the ignition was cutting on the track. The tuners keep telling me that that signal is sheilded.

 

Can you read my megasquirt settings and tell if they are all cool?

 

Should the sending ring be fixed to the balanced part or the solid part of the crank pully?

 

Thanks again

 

Drew

[z-ya]

OK, if it is sheilded, then that is not the problem.

 

You are running EDIS? I would mount the trigger wheel to the solid part of the crank pully (not rubber isolated). Just in case at high rpms the damped pulley distorts, it could effect the gap between the sensor and the trigger wheel. I dought this is the problem as BRAAP has his mounted to the damped pulley and hasn't had problems. You have no more than 1mm between the VR sensor and the trigger wheel, right?

 

Yes, I can check your settings, send me a PM.

[Guest 200sxBoY]

The tps wire was never shielded . and it doesn't need too may i add

MS doesn't suply any shielding for the 5Vref and the TPS wires and if i remember right there is nothing about shielding the tps wire in the whole megasquirt.info site

I have been in car diagnostic for years now and never once in my life i saw a shielded TPS wire. And i worked on nissan's, honda's, gm's, chrysler's and almost every brand you could imagine. Knock sensor and crank sensors are shielded because the signal is so weak the an induction could false what the sensor actually sends.

The tps "glitches" you see is the TPSacc , which stands for TPS ACCELERATION . And if you look carefully, when the TP signal (purple) goes down , the TPSacc also goes down which means the MS senses a deceleration and enable the deceleration mode. When the TP signal goes up, the TPSacc goes up also to show it's in acceleration mode. The number it goes too is just the "number" of enrichement it's giving , so if you snap the throttle really fast the TPSacc will go to let's say 110, and if you snap it gently it may go to 104.