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Herky-jerky response to extra throttle.


gr8scott

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I've posted before about a jerky/bumpy reaction when I press down on the accelerator when approaching a slight uphill. There are no error codes. I've eliminated the transmission as a possible cause because I'm now able to recreate that temporary hesitation with the transmission in park. A tap or sudden flooring of the accelerator does it. It's a jerky feeling like the engine ran into some solid resistance, and then it catches up. . As mentioned before, I can accelerate smoothly from a standstill at the bottom of a hill to cruising speed, as long as I keep constant, gradually increasing pressure on the pedal. It's only when the vehicle reaches a constant speed on level ground and then approach an uphill that the slightest extra throttle will cause that jerk. I don't want to break anything so I've parked it until I get an idea of what it is, or an opinion that it's safe to drive it a few miles to a repair facility. I'm not a car-guy, so please help by suggesting some things to check. TIA.

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Guest phonedawgz

A coating of oil or dirt on a MAF sensor wires can give the trouble you are experiencing. The baked on dirt insulates the MAF wire. A sudden change in air flow is detected in a delayed manner. That results in a delay in acceleration when the throttle is opened quicker.

Using an oiled air filter can cause this problem to happen repeatedly.

If you car uses a MAF sensor and the wire of the MAF sensor shows a baked on coating, it can be carefully cleaned off.

If your MAF is held on by Security Torx screws, either you can cut a screwdriver slot in the screws with a dremel tool, or you can purchase a large assortment of security Torx and other bits are Harbor Freight for about $15.00

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Guest Mc_Reatta

I'll throw the TPS into the mix as well. A dead spot on the conductor will give a glitch when the wiper passes over it resulting in a hitch in performance.

Sorry we can't be more helpful in narrowing you problem down, but I believe no matter the cause, it's perfectly OK to drive your car to the shop to have it worked on.

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I know I have a SCed engine but I had the same symptoms for around a year. Thought it was the SCer belt slipping, but finaly the fuel pump gave out and fixed it. I really suggest checking the pressure to see where it is. You can pick up a fuel pressure tester for $20 (assuming you do not have one). Als the test takes 10 minutes start to finish, five if you hurry.

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I've removed, cleaned and replaced the MAF sensor. Also replaced the air filter. Power increased, acceleration is snappier, but the jerkiness remains. I've read up on the TPS suggestion and realize it's beyond my level (or lack of) expertise to touch it as it would lead to no good. Next I'll get a fuel pressure tester, and do that check. I found a good tutorial on it at:

Reatta Owners Journal - The Buick Reatta Community

One thing I'll need to know before I tackle that is how do I remove the plastic cover from the manifold? I don't see any clips, screws or other fastening devices on it.

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One thing I'll need to know before I tackle that is how do I remove the plastic cover from the manifold? I don't see any clips, screws or other fastening devices on it.

The plastic cover will come off very easily. There are 6 areas that hold the cover onto the top of the manifold.

post-91942-143141990118_thumb.jpg

Hope this helps.

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Scott,

Get your fingers under the edges of the cover and pull up. The clips are molded to, and are part of the cover. You may have to maneuver the cover around a bit as there are fuel lines and other such stuff to get around but, nothing really needs to be removed to allow the cover to come off.

John F.

Edited by Machiner 55 (see edit history)
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I really suggest checking the pressure to see where it is. You can pick up a fuel pressure tester for $20

I've bought two so far: one from Sears and the other at Harbor Freight. Neither of them had a matching fit for the Schrader valve. Others I've found even state on the box that they're not for GM throttle bodies.

Any recommendations on a brand?

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Guest Corvanti

the one Ronnie shows above ^^^ is the one i have. no problems at all with fitting the "schrader valve" - there should be several fittings in the box that fit most vehicles.:)

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That's the same model I got from HF. The fitting that should have fit didn't. It had a gasket that protruded past the thread so it was impossible to get the thread started. I took it back for exchange, and the one I got now appears to have the proper gasket in it as it's recessed enough to get the thread started. It does fit, and I'll do the test tomorrow.

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I have not read the tests but the pressure should increase by 10 psi or so when under throttle. If it is not I would guess the regulator is bad. Glanced at the write up and looks good, but I did not see a test for under throttle. It may be there I only glanced. If you did not hit the throttle and watch for the gauge to jump I would do so. just to ensure all is well. You also said you can recreate the symptom. I would check when it is being recreated.

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Update: I ran the fuel pressure test. With engine off it was 42 psi. At idle it remained the same. Under load it dropped to about 35psi. From what I read this indicates a bad fuel pump or clogged fuel filter, and replacement of the fuel filter is indicated as a first step. Ahem, but I don't know where that is. I looked into the manual, but the only reference is this murky illustration, and I can't make out a location from it:

post-31407-143142000862_thumb.jpg

I also wanted to run the recommended Load Test, but was unable to locate the "green fuel pump prime/test connector" unless it is this:

post-31407-14314200087_thumb.jpg

Testing the fuel pressure regulator, I found the vacuum line thoroughly stuck, so I couldn't remove it, assuming this is the pressure regulator:

post-31407-143142000874_thumb.jpg

If confirmed that it is the right thing, I'll wrestle with it again.

I'm not a car guy, and am about as dangerous around an engine as a doctor in a small plane. I find it safer to ask first, even if it shows my ignorance.

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Guest Corvanti

the fuel filter is under the driver's side door and up a little towards the engine. it's a PITA to remove... i think '91's may be different.

the other 2 pics are correct in location. try some PB Blaster on the regulator hose to loosen - same with the fuel filter connections.

i'd start with a jumper wire from the positive terminal of the battery to the green connection to get another reading on the fuel pump pressure at different rpms. then the regulator test. and what Daniel says to "re-create" the problem...

regarding the fuel filter: mine was so tight i'd probably have "farmed it out" if i had known how tight it was.:(

hope this helps, and hope more info comes your way!

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Might also verify that, with the engine running, you have 12-14v on the green connector.

ps '90s went to snap in connectors in the fuel line. Every time I change the fuel pump I also change the fuel filter.

pps dunno why the factory hires gorillas to tighten the connections. Suspect they do not have time to check for leaks so makes sure there aren't any. If you make sure the surfaces mate properly it does not take much force to make leak free.

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42-43 psi with key on and engine off is about correct. It should drop with the engine running in response to engine vacuum, probably to the mid-upper 30's for fuel pressure at idle. It should blip back up to the low 40's when the throttle is snapped open and return to the mid-30's when it returns to idle. If it remains at 42'ish pressure at idle, the vacuum diaphragm or line to the regulator is defective. You do need to get the vacuum line off to check for vacuum when running and also for evidence of fuel in the vacuum line. It should never drop below the mid'30's in any running condition. If so, the filter or pump is plugged or failing. The fuel filter first is a good place to start, as suggested, as well as the regulator itself.

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After I submitted the link to the Fuel Pressure Testing tutorial on my website, there have been several comments about how the fuel pressure should be checked. If my instructions have errors or omissions please let me know about them. I'm always willing to make changes when needed. I want the tutorial to be as clear and concise as possible.

Please keep in mind that the Fuel Pressure Testing tutorial was intended to be a test of the fuel pumps ability to maintain pressure to the fuel injectors. Testing the fuel pressure regulator was intended to be in a separate tutorial that I have not gotten around to yet. - BTW, that is the reason the vacuum pump is shown in the list of tools used and that is the reason the regulator and the vacuum line going to it are labeled in the photos.

Edited by Ronnie (see edit history)
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I think the average joe must join and get a password to link to the site? I just clicked on it and asked for authorization? I'm sure it's good test info. I only mentioned the regulator as it was brought up in a prior post. Essentially a fuel injector is flow rated at a specific differential pressure, the difference between the intake manifold pressure or vacuum and the fuel pressure. The regulator "sees" the vacuum in the intake manifold and reduces fuel pressure to keep the relationship stable. The vacuum pump can simulate the manifold vacuum. Approximate value is 1psi for every two inches Hg manifold vacuum. It also works in reverse when the manifold is pressurized due to turbo or supercharger and raises fuel pressure in a direct relationship to the amount of boost. The regulator is a separate issue from the fuel pump but if it malfunctions and keeps the pressure higher than required it does put more strain on the fuel pump. A boosted engine is even more sensitive to the ability of the fuel pump to keep up. An engine running up to one bar of boost will need to maintain flow at up to 60 psi or so, usually requiring an upgrade.

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Guest Corvanti
If I had realized about six years ago that posting a link to the FSM was so much easier than writing a tutorial I sure could have saved myself a lot of work. :D

Ronnie, as i have said in the past, the FSM was written for Mr.Goodwrench in his dealer's service dept, with virtually all needed "special" tools available and does the work on a daily basis. the "Tutorials" seem to be written more for us "shadetree" mechanics that may do a specified repair only once in the time we have the vehicle.

while i do check the FSM before repairing my Reatta, i also see if there is a Tutorial on the subject and find them most helpful!!!:)

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I'm somewhat confused about this: "I'd start with a jumper wire from the positive terminal of the battery to the green connection to get another reading on the fuel pump pressure at different rpms"

I ran the Fuel pump load test as per Ronnie's journal green test connector and negative post of battery) with the key on Run and got a reading of 10.9 Volts. Are these two different tests?

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I'm somewhat confused about this: "I'd start with a jumper wire from the positive terminal of the battery to the green connection to get another reading on the fuel pump pressure at different rpms"

I ran the Fuel pump load test as per Ronnie's journal green test connector and negative post of battery) with the key ON but engine not running, and got a reading of 10.9 Volts. Are these two different tests?

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Guest 89 Maui

The confusion is the green connector needs a jumper wire to the positive terminal of the battery. By putting +12V from the battery to the green connector puts 12V directly into the fuel pump. This bypasses all wiring and fuel relay. You will then hear the fuel pump running. Then measure the fuel pressure on the injector rail.

You may have a weak fuel regulator which may be letting some fuel pressure head back to the fuel tank.

Woody

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Guest Corvanti

...and, if i recall correctly, the key should be in the off position or out of the ignition switch. the jumper wire runs directly from the battery to the fuel pump.

thanks, Woody!

i was looking thru the FSM to see if my "oldtimers" was kicking in again!:rolleyes:

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Guest Mc_Reatta

Only reason to worry about that green connector is to figure out a problem with getting power to pump if it isn't working. Can tell you if the fuse or relay isn't working or the pump is getting power but is broken.

That's not your problem. Your pump runs, your just trying to figure out if your getting good pressure from the pump, your filter isn't clogged, the vacuum pressure regulator is working, and the pump seals are not letting the fuel drain back into the tank too quickly dropping the rail pressure and making restarts harder.

Those tests are well documented in the FSM as are some injector tests.

By the way, think you need to charge your battery. 10.9 volts key off is pretty low. Check it at the battery. If it's 12 volts, then you've go some bad connections between it and the pump.

Getting registered on Reatta.net and getting access to all that good info and documentation is part of the holy trinity of things to do for new Reatta owners.

(This site and Ronnie's site are the other two)

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<I>"I have a problem with clicking the "Submit" button."</i>

I can't even see the Submit button. I clicked on the Reply, and when I didn't see my message I posted it again, and then both were up. When I tried to delete the duplication, both got deleted. When I reposted it (once) both got reposted. Thus the dual post (#28 and #29)above.

By the way, one of the tests indicated that the fuel pump fuse should be checked. There is no fuse marked Fuel Pump in the cabin fuse panel. The Service Manual makes no mention of one anywhere else.

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Guest Mc_Reatta

Don't worry about your problems with being submissive. :rolleyes:

Since only those without problems are allowed to cast stones, there would not even be a need to duck.

Fuse is not the problem as your pump runs, but in an 80's it is on the firewall above the fuel pump relay. In a 90's it is inline inside the console behind the relay center.

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"I have a problem with clicking the "Submit" button."

I can't even see the Submit button.

Scott,

You are correct. There is no "Submit" button any longer. But, at one time before the Forum was updated/upgraded, there was a "Submit" button.

It was then that I put that statement in my sig. There are still "Submit" buttons on other sites and I still have a problem with them. :)

John F.

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Guest Mc_Reatta
"By the way, think you need to charge your battery. 10.9 volts key off is pretty low. Check it at the battery. If it's 12 volts, then you've go some bad connections between it and the pump."

Battery measures 12.6V.

You're probably AOK then. There's a lot of draw on the system in run and without the alternator running I wouldn't expect battery voltage to be maintained. If you're worried check it with engine running, and I bet you will see 13+ volts.

You haven't said what pressure reading your seeing on the gauge, but I think you're barking up the wrong tree looking for the source of your problem.

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"I'd start with a jumper wire from the positive terminal of the battery to the green connection to get another reading on the fuel pump pressure at different rpms"

So this is with the engine running, right? And we're not talking about a multimeter reading between the negative battery cable and the green test connector, but a pressure reading off the pressure regulator. Someone above called it a vacuum regulator, and again I assume it's one and the same.

One reason why this thread may have gone FUBAR is due to my piecemeal response to clarifying questions, but I had to go buy a pressure test kit, and then a multimeter, and now I'm going back for a jumper wire to conduct the above test, plus an assistant is not always available when I need one. Please bear with me.

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Guest Corvanti

sorry if i mis-stated or didn't make it clear.:o the jumper wire is used with no key or ignition on. a 12 or so gauge wire with alligator clips homemade will work from the positive battery terminal to the green wire will work. put the fuel pressure gauge on the schrader valve as stated before. that will give you a reading of the fuel pump bypassing the other stuff.

i'm starting to think this is NOT your problem, but should rule it out before going further...

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