Jerky throttle :(

[Geoff]

Thanks...will try that next if the MAF doesn't resolve it.

[Geoff]

Let me add - This seems to be intermittent. This morning, throttle was fine. Bizarre. Points to an analog sensor, I suppose.

[injuhneer]

Originally Posted by Geoff

Let me add - This seems to be intermittent. This morning, throttle was fine. Bizarre. Points to an analog sensor, I suppose.

*bump*

Was this ever solved? My '94 is doing something very similar. The throttle tip-in is abrupt. The progression is sudden.

I will check TPS for adjustment and operation first but was wondering if a cause was determined.

-Mike O

[Crazy_pilot]

Sounds a little bit similar to something my car does. When accelerating it's almost like there's a dead zone in the power band from 1100-1400 RPM. Below or about that is fine. It never gets rough or anything, just feels like I'm pulling a boat anchor at those engine speeds and the car has to be forced to pull through to higher speeds.

In my case this problem has survived the bead crush mod, new TPS, one new knock sensor, head gasket replacement, a complete engine swap, a manual conversion, and a few other things. (Note: Most of those things were fixes for other problems. I didn't swap the engine to try curing a hesitation)

[icingdeath88]

Originally Posted by Crazy_pilot

Sounds a little bit similar to something my car does. When accelerating it's almost like there's a dead zone in the power band from 1100-1400 RPM. Below or about that is fine. It never gets rough or anything, just feels like I'm pulling a boat anchor at those engine speeds and the car has to be forced to pull through to higher speeds.

In my case this problem has survived the bead crush mod, new TPS, one new knock sensor, head gasket replacement, a complete engine swap, a manual conversion, and a few other things. (Note: Most of those things were fixes for other problems. I didn't swap the engine to try curing a hesitation)

Does it do this any more or less when hot/cold?

[injuhneer]

Originally Posted by icingdeath88

Does it do this any more or less when hot/cold?

In my case it is only moderately more noticeable when cold but is still there after warm-up.

It behaves as though the throttle goes from closed to 1/4 open the instant the pedal is pressed. I had not equated it to engine RPM because it seems to be more throttle position related.

I thought maybe the TPS could be out of adjustment but the original paint marks are there from the factory. So I am thinking possible a dead spot in the TPS at tip-in or it is maladjusted and sending an incorrect value to the ECU.

-Mike O

[oab_au]

Originally Posted by injuhneer

In my case it is only moderately more noticeable when cold but is still there after warm-up.

It behaves as though the throttle goes from closed to 1/4 open the instant the pedal is pressed. I had not equated it to engine RPM because it seems to be more throttle position related.

I thought maybe the TPS could be out of adjustment but the original paint marks are there from the factory. So I am thinking possible a dead spot in the TPS at tip-in or it is maladjusted and sending an incorrect value to the ECU.

-Mike O

Mike the TPS should not affect the way the engine increases speed. The TPS is used mainly to report engine load.
The cable opens the throttle, the MAF sensor measures the air flow, the ECU injects the right amount of fuel, and the engine increases speed.

So unless the cable is sticking or such, the ECU is not responding, to inject fuel. This seems to be a US thing, that does not happen to Aust cars, maybe an emission thing?

Harvey.

[Crazy_pilot]

Originally Posted by icingdeath88

Does it do this any more or less when hot/cold?

I've put so few miles on the car in the past year it's hard to remember. Something is telling me it's mainly a cold problem, but has also happened hot. And it's intermittent, just to keep things from getting too easy.

Harvey, I'm not sure what emissions equipment would cause this as I've removed both my EGR and charcoal canister systems with no affect on the hesitation. The only original exhaust related parts are the manifolds and O2 sensors.

[oab_au]

Originally Posted by Crazy_pilot

I've put so few miles on the car in the past year it's hard to remember. Something is telling me it's mainly a cold problem, but has also happened hot. And it's intermittent, just to keep things from getting too easy.

Harvey, I'm not sure what emissions equipment would cause this as I've removed both my EGR and charcoal canister systems with no affect on the hesitation. The only original exhaust related parts are the manifolds and O2 sensors.

No not the Emission equipment Chris, just the ECU fuel/spark maps, that are set for the US market's restrictions.

Harvey.

[bishop]

i sort or have this problem except its only a rough idle after doing plugs and timing belt, once im going its fine, though the engine does seem a little touchy when cold.

[injuhneer]

Originally Posted by oab_au

No not the Emission equipment Chris, just the ECU fuel/spark maps, that are set for the US market's restrictions.

Harvey.

Are all US cars doing this? If so then it becomes a matter of correcting the map. If not then I am still inclined to think it is related to the TPS. There is a delay, however small, between the time your foot opens the throttle plates (changes TPS output) and when the MAF detects the change in air flow.

This could be an ECU map problem but then all cars would have it from new, correct? If I had driven a new car and felt this there is no way I would have purchased the car.

If there is a dead spot in the TPS or it is adjusted out of range then the effect is:

Press the pedal. No initial change from the TPS. The MAF catches up a moment later and the surge follows. The result is what feels like abrupt tip-in on the throttle.

Of course my '94 isn't OBDII or I would already have plugged into see where the hesitation that results in the surge is originating.

-Mike O

[injuhneer]

Update:

Inspection located a split in the aux air hose. Remedied that. Drove it and there was some improvement.

Removed the TPS and measured it across the sweep; 0.160kΩ to 4.71kΩ. Installed it again and adjusted to 0.5v. Drive car; no change. Adjust back to 0.47V (measured before removal); car drives about the same. Adjusted to 0.55v. Drove car; a definite change for the better. The surge is not completely gone but the off-idle throttle tip-in behavior is much better.

-Mike O

[longassname]

Mike,

If you have a laptop with a 32 bit version of windows you can use an ECUtuner select monitor interface and the free ECUtuner software to monitor up to 4 parameters at a time. In this case, monitor ignition advance and retard and you will quickly find the culprit. I'll explain this below but let's say you did have a bad tps. Using the ECUtuner software you could monitor it and see exactly how it works. If there were a dead spot it would show up as bright as day in a few minutes instead of scratching your head for days..or weeks..or is it months now? Same goes for any other sensor that might be suspected.

Ok, now the explanation of what I would expect to be your problem. The SVX engine control unit uses two ignition timing tables. The verticle axis is rpm the horizontal axis is load. Load increases from left to right. RPM increases from top to bottom. The ECU starts with only the ignition advance specified in the primary table and then uses an algorythm with the knock sensors to learn in additional advance up to the maximum specified in the revision table. So the maximum ignition timing possible is the primary and revision tables added together. I'm posting both tables and below them a table which is the two added together. I'm posting them in normal decimal values so the #'s you see are the actual normal #'s a normal person knows and understands.

Load is the mass of air in a single cylinder. The ECU calculates it from the mass air meter signal, the known # of cylinders, and the rpm. Things like air temperature, weight of the car with ocupants etc, and how far you are pushing the gas pedal effect it. The colder it is, the heavier the car, the further you push the pedal the higher the load and the further right in the table you are operating in. You say your hessitation is around 1400 rpms..depending on the weather, condition of your engine, occupants, how much gas you have in your tank etc you would be operating in the area of the 10th, 11th, 12th, or 13th column. I'll color the font to identify the area. Looking at the primary table you will see there really isn't enough ignition timing there for the engine; your engine simply will not perform without learning in additional advance. Looking at the revision table you will see that they want and expect the ECU to learn in A LOT of advance. Looking at the combined table I made up you can see how much timing the car would like to be running. If you monitor your timing with the ECUtuner software when you have the big hessitation you will find you are running much closer to the value specified in the primary table than the combined value you would like it to be. SVXs simply have problems learning in advance with the crap gas our government regulators demand that we be sold here in the US. Here's where it really gets good......if you tell it to run that timing instead of to try to learn in that timing it runs great. It's not that the car can't run more timing with our crappy gas; it's that it can't learn to run more timing with our crappy gas.

Also..take a look at the next row in the tables. Why does your car suddenly take off after the huge hessitation? Because as soon as your car manages to crawl it's way past 1600 rpms the primary table starts throwing in a lot more timing.


In my Stage1av1 firmware I forgoe the whole learning in of advance and put performance ignition timing in the primary table to begin with; the result is improved performance, improved fuel economy, and no dead spots.




USDM PRIMARY
600 35 30 24 23 21 10 06 02 00 00 00 00 00 00 00 00
800 31 31 28 23 21 17 14 10 05 02 00 00 00 00 00 00
1200 35 35 32 28 25 21 15 11 09 04 02 01 00 00 00 00
1600 43 43 40 38 35 30 24 19 17 14 11 10 07 04 00 00
2000 45 45 43 41 39 35 32 25 23 21 19 18 15 11 07 04
2400 50 50 50 50 50 44 37 30 27 24 23 22 16 12 08 04
2800 50 50 49 49 48 46 43 38 34 28 25 24 20 15 10 05
3200 50 50 50 49 49 47 44 41 38 34 30 28 25 19 12 06
3600 50 50 50 49 49 48 46 44 41 37 33 29 27 21 14 07
4000 50 50 50 50 49 48 46 44 42 39 35 31 26 21 14 07
4400 50 50 50 49 47 44 42 40 37 32 32 29 26 23 15 10
4800 48 48 48 47 45 43 41 39 37 35 32 29 26 24 15 10
5200 48 48 48 47 45 43 41 40 38 36 31 29 25 23 15 10
5600 50 50 50 48 45 42 38 35 33 31 29 27 25 23 17 13
6000 50 50 49 48 47 45 43 41 39 37 33 29 25 21 17 13
6400 50 50 49 48 47 45 43 42 41 38 35 33 30 26 22 18
rpm



USDM REVISION
600 00 00 00 00 00 05 05 05 04 02 00 00 00 00 00 00
800 00 00 00 00 00 04 05 05 08 09 08 05 02 00 00 00
1200 00 00 00 00 00 01 03 05 06 10 12 13 11 08 02 00
1600 00 00 00 00 00 03 03 05 05 08 09 09 10 09 09 05
2000 00 00 00 00 00 00 02 04 05 05 07 06 07 08 07 06
2400 00 00 00 00 00 00 01 04 05 05 05 05 09 10 08 07
2800 00 00 00 00 00 00 00 02 03 04 05 07 09 11 12 11
3200 00 00 00 00 00 00 00 02 03 03 04 07 08 11 15 18
3600 00 00 00 00 00 00 00 00 02 04 06 08 07 10 13 15
4000 00 00 00 00 00 00 00 00 01 01 03 05 08 10 12 15
4400 00 00 00 00 00 00 00 00 02 06 05 06 05 06 09 10
4800 00 00 00 00 00 00 00 02 03 02 04 05 05 06 06 05
5200 00 00 00 00 00 00 00 00 01 01 03 04 05 04 06 05
5600 00 00 00 00 00 00 00 03 05 05 04 04 05 03 05 04
6000 00 00 00 00 00 00 00 00 00 01 02 04 05 04 05 05
6400 00 00 00 00 00 00 00 00 00 02 03 02 02 03 02 02
rpm


COMBINED
600 35 30 24 23 21 15 11 07 04 02 00 00 00 00 00 00
800 31 31 28 23 21 21 19 15 13 11 08 05 02 00 00 00
1200 35 35 32 28 25 22 18 16 15 14 14 14 11 08 02 00
1600 43 43 40 38 35 33 27 24 22 22 20 19 17 13 09 05
2000 45 45 43 41 39 35 34 29 28 26 26 24 22 19 14 10
2400 50 50 50 50 50 44 38 34 32 29 28 27 25 22 16 11
2800 50 50 49 49 48 46 43 40 37 32 30 31 29 26 22 16
3200 50 50 50 49 49 47 44 43 41 37 34 35 33 30 27 24
3600 50 50 50 49 49 48 46 44 43 41 39 37 34 31 27 22
4000 50 50 50 50 49 48 46 44 43 40 38 36 34 31 26 22
4400 50 50 50 49 47 44 42 40 39 38 37 35 31 29 24 20
4800 48 48 48 47 45 43 41 41 40 37 36 34 31 30 21 15
5200 48 48 48 47 45 43 41 40 39 37 34 33 30 27 21 15
5600 50 50 50 48 45 42 38 38 38 36 33 31 30 26 22 17
6000 50 50 49 48 47 45 43 41 39 38 35 33 30 25 22 18
6400 50 50 49 48 47 45 43 42 41 40 38 35 32 29 24 20
rpm

[injuhneer]

Originally Posted by longassname

Mike,

SNIP

Load is the mass of air in a single cylinder. The ECU calculates it from the mass air meter signal, the known # of cylinders, and the rpm. Things like air temperature, weight of the car with ocupants etc, and how far you are pushing the gas pedal effect it. The colder it is, the heavier the car, the further you push the pedal the higher the load and the further right in the table you are operating in. You say your hesitation is around 1400

The hesitation my car is exhibiting is off-idle (600-800 rpm) but does reduce 1500-1600 rpm. In any case I see your point.

So here is a question about the effect of what I did: does the ECU read the voltage from the TPS as a zero reference or does it use chassis ground as zero?

-Mike O

[icingdeath88]

Originally Posted by injuhneer

The hesitation my car is exhibiting is off-idle (600-800 rpm) but does reduce 1500-1600 rpm. In any case I see your point.

So here is a question about the effect of what I did: does the ECU read the voltage from the TPS as a zero reference or does it use chassis ground as zero?

-Mike O

There are 3 wires that go from the ECU to the TPS: ground, +5V reference, and signal. So I believe that it uses an ECU ground for the ground reference.