97 Regal GS Hesitates while driving

[jayjay444]

While driving at highway speeds car seems to drop rpm's and goes back to normal with in a few seconds. I can get it to stop doing this by giving the car more gas. Problem will go away on it's own and doesn't come back for a week or two, sometimes longer. The car has 132000 miles with new injectors, fuel filter, EGR valve, plugs, wires, and fuel pump speed control relay. Thanks in advance for any help. jayjay

[HotZ28]

Originally Posted by jayjay444

While driving at highway speeds car seems to drop rpm's and goes back to normal with in a few seconds. I can get it to stop doing this by giving the car more gas. Problem will go away on it's own and doesn't come back for a week or two, sometimes longer. The car has 132000 miles with new injectors, fuel filter, EGR valve, plugs, wires, and fuel pump speed control relay. Thanks in advance for any help. jayjay

Do you have this problem with the cruise control on, or just using the foot pedal? Have you checked for any codes? It is important to verify if you have a “misfire” during this rpm drop! Check the TPS performance on a scanner for proper operation. Also, check and clean battery connections with a brass brush and lubricate with dielectric grease. Be sure to check all ground connections!

[jayjay444]

I unhooked MAF sensor to see if it would act up in limp-mode; of coarse it still does it. No prior codes before unhooking MAF. Plan on checking grounds & TPS connections tomorrow. Problem happens with cruise on or off. Can I check the TPS with a OBD II scanner? After searching AF my car does what people call chuggles or fishbites, any ideas on this? jayjay

[HotZ28]

Is this happening with torque converter engagement? Normally, the "fish-bite" condition would be torque converter chatter, caused by a defective clutch, solenoid, or valve body. If this were a misfire condition, you should get a P0300 code. Yes, the TPS can be checked with an OBD II scanner.

[BNaylor]

Originally Posted by jayjay444

Can I check the TPS with a OBD II scanner? After searching AF my car does what people call chuggles or fishbites, any ideas on this? jayjay

It could very well be "fishbite or "chuggle"? When was the last tranny service. ATF and screen filter?

Chuggle/fishbite is the effect of a problem that causes the torque convertor (TCC) to lock and unlock which gives a jerking feeling typically while under a load such as going up a hill or incline. It could be a TPS, spark plugs, ignition wires, coil pack, 02 sensor (if closed loop mode), tranny or other issues.

GM has a TSB out on the issue and claims the TPS sensor is the cause but replacement very seldom if ever corrects the problem. You can check the TPS output with a DMM but a bad TPS on an odb-ii system will normally generate a DTC.

I would get it scanned with a trans capable scanner and one that can detect GM extended DTC codes. Some DTCs related to the autotransaxle (4T65E-HD) may not trigger a SES/CEL MIL light but store for retrieval.

A simple test to see if the torque convertor is working properly is to drive on a straight, level road. Make sure you are in D (OD-4th). Take the speed up gradually to above 45 mph. Watch the tachometer. When the TCC engages you will see a dip of a few hundred rpms. Then tap the brakes to see if it disengages and rpms should dip up.

[jayjay444]

Checked battery connections and power lead terminations. Battery positive connector a bit corrosive, cleaned and greased; negative looked good greased. Removed and inspected negetive termination at bell housing, looked good. Removed bolt on chassis ground and polished to bare metal, reinstalled and greased. (had battery on charger for 2 hrs while working on connections).Also cleaned connector to TPS and pulled MAF and sprayed the shinny objects in the "tunnel" with electric cleaner. Took car out for test, 25 minutes of driving and it started to drop in RPM and regain while cruising at 65MPH. Put car into 3rd and it still did the drop and regain (don't think it's the tourqe convertor??) this episode lasted about 15 secondsNext I pulled trunk access cover and put my digital volt meter across the fuel pump leads, drove for another 45 minutes with it driving fine. DVM would read 10.2v - 10.6v while the fuel pump speed control relay was in control and 12.2v - 12.8v while not. How can I check the fuel pressure at the rail while driving?? Are the above voltages legitamate? Car only seems to act up while at highway speeds. Have actron Model CP9135 OBD ii scanner, not sure if it will display the MAF or TPS feedback; will look in on that now or do you know if my scanner is capable of it?

[BNaylor]

The CP9135 is just a generic odb-ii scanner and won't even read GM extended DTC codes. The CP9145 does. Before you monitor fuel pressure at the front rail during a test drive what are the fuel pressure readings at fuel pump prime (ignition on) and idle with and without vacuum connected at the fuel pressure regulator? Does it meet GM specs?

If you don't have one Actron makes a good fuel pressure tester and comes with the connection for the Schrader valve.

On the fuel pump speed control relay bend pin 85 down (open circuit) to put it in resistor bypass mode so the fuel pump runs at high-speed only.

[jayjay444]

Got a fuel pressure tester: reading at rail was 55 psi for the 2 second charge at ignition on. While starting it would read 55 psi, dropping to 48 psi when running. With vacuum line disconnected from the fuel regulator, the pressure reading was also 55 psi. GM specs are 48-55 with ignition on, and 3-8 psi less than ignition on reading while running.

Today the car didn’t want to start too great; cranked over for 6 seconds without starting. On second attempt of cranking it started after approximately 6 seconds. No codes were set. Seems these episodes happen 1-2 times out of 20 with the engine not starting as quick as usual. (always starts w/in 2 seconds, except for it’s “episodes”).

Today the car drove fine, no drop in RPM and return while driving. I tested the pressures after we got it home. Didn’t have gauge along to check readings when we had the trouble starting.

Am I on the right track?? Is it common for a fuel pump to be fine one day and not the next? I’ll keep the gauge in the car. Any ideas on why the RPM fluctuation would happen at highway speeds and not while at idle or at less than 40 MPH??

[BNaylor]

Your overall fuel pressure readings appear good. The part that may be questionable or marginal is the amount of fuel pressure difference when vacuum is removed from the fuel pressure regulator. It looks like it is borderline. A bad fuel pressure regulator will cause difficult or long starting. It sounds like you may need to connect the gauge where you can view it while driving to rule out a fuel supply problem.

The only component electrically that I can think of that may give similar symptoms is the crank position sensor. When the stall occurs do you get any IP idiot lights? Like trac off? Doesn't always give a SES/CEL light either.

[bigciccone]

sounds like the same thing thats wrong with my regal.. about 99% positive its the coil pack.

[jayjay444]

We changed the coil pack about 10,000 miles ago and the car still did it. It hasn't done it now for over 1,000 miles after cleaning all electrical connections. I hope that is all it was. jayjay