W.E.G.

I'm in the process of various "experiments" with my patient.
Patient has started "stuttering" again. AKA bucking bronco and various other descriptions of the sypmtom.
In particular, I wanted to know whether I was losing fuel pressure when the stuttering happens.

Test went well.

I never had before done a fuel pressure test, so this was definitely a learning experience.

$30 gauge from Amazon seemed to do the trick.
Amazon link:

Showing currently as unavailable on Amazon, but available for even less money on eBay.

I took the advice of several reviewers, and I used Teflon tape to seal the threads at the manifold and at the gauge. I had no leak problems.

I had one snag. On first connection of the gauge, I was getting no pressure at the gauge, even though I was sure I had a tight connection at the manifold. I removed the connection from the manifold, and I discovered that the rubber seal inside the connector was mashed/mangled. I'm pretty sure I must have mashed the seal over the Schrader valve in such a way as to block-off the port in the hose. So, I just removed the rubber seal from the connector altogether, and I reattached the connector to the manifold. When I turned the key on, I heard the fuel pump activate, but the gauge still was showing zero. When I started the motor, the gauge immediately shot up to the mid-30's, and held steady.

I went for a 40-minute drive with the gauge snaked up between the hood and the cowl in such a manner that I could see the gauge while i was driving.

During the drive, pressure ran from 32 to 42. Mostly at about 34 during off-load throttle, and as high as 42 during heavy-load.

The car did stutter several times after the ECM switched to closed-loop function. During the stutter, the gauge stayed steady, or if I gave extra throttle, the gauge would go up to 40-42.

Information gained is this: I am not losing fuel pressure during the stutter episodes. Has to be something other than the fuel pump. The stutter seems to happen most often at very light throttle. I'm beginning to suspect it may be a throttle position sensor, and that the conductive area of the potentiometer in the light-throttle range in the sensor has become worn-out, causing a "dead zone" in the throttle. No info to the ECM from the sensor would mean no fuel delivered to the motor while the potentiometer is in the dead zone. The throttle seems to "come back" after I give it more push when the bucking starts.

A few pics of today's work:


Idling in driveway before engine warmed up.



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Running about 2500 rpms in driveway before engine warmed up




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After shutoff after the 40-minute drive.



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pic of gauge set from Amazon

3.4 grape

iTrader: (1)

Tps is what I thought of also if it's old I would replace anyway. Is that the correct fuel pressure for your car? I have a forth gen and pressure is normally around 40 lbs at idle.

W.E.G.

The manual says 40-47 psi pressure is the the spec.

So, if this gauge is calibrated correctly, my pressure is below spec.

The main purpose of the test was to see if there was some sort of loss of fuel pressure right before the bucking-bronco act. Fuel pressure remained constant during the bucking-bronco act. If I put my foot in it during the bucking, it would buck hard a few times and then come to life and run normal(ish). If I put my foot in it during the bucking the fuel pressure would go up to around 42.

What I failed to do in this test is pinch-off the return line to see what kind of numbers appeared on the gauge. The fuel pressure regulator is the original regulator, so it seems likely that the regulator could be part of the overall issues of the car.

I went ahead and parts-cannon-ordered a throttle position sensor after the test. Should arrive in a few days. So much to look forward to!

3.4 grape

iTrader: (1)

That sounds about right, should be about 40 at idle and 47 at full throttle. If you pinch off the vacuum line (not the return line) when at idle, the fuel pressure will go up to the max.

zs&tas

Last year when I had a similar problem , I had a vacuum leak, upper to middle i take .
i now have a part throttle occasional miss this year, I'm not sure what is going on there , it will be interesting to see what happens with your tps, did you actually test your current one ?

W.E.G.

I did not yet test my existing throttle position sensor.
I may attempt to voltage-test the old TPS when the new one arrives.

The fact that the bucking bronco problem is intermittent causes me to have doubts about information I may gather by voltage-testing the existing TPS. That is, 99% of the time, when I press the gas pedal, I do not get treated to the bucking bronco assault. Which makes me think I only have a 1% chance of the failure showing up on a multimeter if I test the existing TPS. Add to that, the fact that my chops with the multimeter are still at novice level.

The TPS is so accessible, and remove/install looks to be a 5-minute job maximum. I'm tempted to just wait for the new TPS to arrive, slap it on there, and go for a ride to see if the bucking bronco is finally laid to rest.

I'm also in the process of getting the spare ECU wired to talk to my laptop via the Tuner Pro program. If the bronco is still hanging around, I will be VERY interested to see what kind of data gets logged when the bronco shows up.

OrangeBird

iTrader: (1)

One Man's opinion only ;

Testing any potentiometer based device for an intermittent connection of the wiper is best done with a good old fashioned analog (has a needle on a meter face instead of a display of electronic numbers) meter using the ohms function . With a digital meter the rise and fall of the numbers as the display updates itself will not reveal a "scratchy spot" (bad connection) nearly as well as the needle will display that fractional of a second hesitation of movement as the wiper passes the open spot on the carbon track . It is for this reason that although I far prefer a modern meter for things like fixed voltage checks and actual fixed resistance (ohms) checks , I still keep my trusty "Simpson 260" specifically for checks of variable resistances such as this . It's funny , on audio equipment the open spot is as obvious as a punch in the face , that scratchy sound whenever the volume control passes the bad spot , and in situations like these turning the wiper's action into an actual physical movement (rather than rapidly rising/falling numbers) is the next best thing to being able to hear the scratchy bad spot .

I hope that made some kind of sense , if you can get an analog meter try your checks with both and you'll likely see the analog's advantage in this situation

zs&tas

That is a TOP TIP thanks !

Mark RWC

Analog meters do a great testing the TPS ,a potentiometer or pulsing voltage signals.

For those that do not have an analog meter check the digital meter manual for a bar graph setting. If you have a Fluke digital meter it may have analog bar graph function suitable for testing TPS. Below is from Fluke website.

Analog bargraph for fast changing or unstable signals

OrangeBird

iTrader: (1)

Your welcome and I'm glad to help .

The one other thing I didn't think of till after my post is , if at all possible obtaining a "pigtail" for the TPS , the connector that plugs into the unit with a few inches of wire attached , will make it far easier to connect the ohm meter to the TPS instead of trying to use alligator clips (for instance) to make the connection . Using a pigtail either bought on line or snagged from your local "pick & pull" will make testing the TPS very easy , strip an inch of insulation from the end of the pigtail's wires and wrap the wire securely around your meter's probes and plug in the TPS to be tested . Of course , to insure the best connection possible between the pigtail and the meter's probe you could wrap a few wraps of electrical tape around the pigtail/probe connection to hold it secure .

PS , Mark RWC's suggestion of using the bar graph (if available) if an analog meter is unavailable is a good suggestion indeed , the bar graph will provide that sliding up/down physical movement similar to the analog meter's needle . The needle would of course still be #1 choice but the bar graph option would be a strong #2 choice with the numerical display coming in third ...