2001 Pont Grand Am - 3.4L Surges / Misses FIXED/ NEW PROBLEM

[Ruger77]

2001 Pontiac Grand Am w/3.4L surges; sort of like a miss climbing hills & acceleration. Seems to only happen when torque converter is locked. I also seem to reduplicate at 1.20 - 1.35 V on the TPS but only while driving. Only codes in memory was P1122 Tp circuit (I replaced TPS just to eliminate....scope pattern looked a little fuzzy) & code P1189 Eng. oil press circuit. No misfire codes. Customer just replaced plugs & wires trying to solve problem, but no success. I monitored fuel pressure while duplicating surging at 50 mph & it would fluctuate a little w/the fluctuation in engine rpm but still 50-55psi. Problem does not "feel" like an ignition miss........ it feels to me like your playing with the accel pedal, you can see it on the tach.


Any help greatly appreciated!!

[Ruger77]

I think I may have answered my own question. It appears that the problem is the TCC solenoid or TCC maybe not holding at partial lock. The surge only occurs when the TCC is applied, & I'm getting slip RPM's (100 - 600) that are very erratic during the surging event. If I completely lock or unlock the TCC with the scanner manually, problem goes away. Any thoughts?

[steven kiser]

yes you answered your own question. funny, i've posted issues then saw the answer in the question and deleted the post. it's funny, sometimes when it's written down you can look at it in a different way and solve it. i'm glad you didn't delete and are now a member of the forum. welcome and don't listen to what others say about me. if you do i'll be "forced to add your name to the list of people that really piss me off" calvin, gotta love that little guy. remember just ask away, we're much more friendly that the other technical support groups............

[brianp87]

[Jeff @ Able Auto]

Is that the "sensitive" side Steve

[Ruger77]

I typed the wrong engine size in my first post.... it is a 3.4L. Now I have created a new problem, how to isolate the ECM and wiring, or trans repair, or complete trans replacement / torque converter. Customer is willing to pay more diagnostic time. I have some tests in mind, but any thoughts?

[steven kiser]

how many miles on it and what's the overall condition of the car. i'd drop the pan and check it's contents. if there's more metal in it than under the shop grinder i would suggest an r&r. to answer the sensitive side question, to define some one as being occasionally sensitive wouldn't you have to know their usual disposition.

[Ruger77]

The car is pretty good condition.... but now I'm leaning more toward an ECM than a TCC or solenoid. I can lock & unlock the TCC with the scanner & problem is not there & no slip RPM's (TCC will go to 99%). If I let the computer control TCC engagement, it only goes to about 35-55% duty cycle, never going any higher than 65%, and she slips from 100 - 600 rpms but with no codes. According to my research, the ECM controls TCC solenoid duty cycle based on slip RPM's, and when it see's that high, it should raise the duty cycle (which it doesn't) & over 200 slip rpm's should set a code (which it hasn't). On the datastream we are looking at ECM COMMANDED duty cycle of only 35-55% when clearly the ECM is seeing a high enough slippage to warrant COMMANDING a higher duty cycle. I thought originally maybe the solenoid was just bouncing at midrange, until I found out that I'm looking at commanded duty cycle, not actual. I think I'm going to recheck my grounds & wiring, then order an ECM. Am I in the giggleweeds with this theory?

[steven kiser]

as a rule if the scanner can control the transmission without an issue it is the pcm. however, i would replace the solenoid before i did any more diagnostic work. it probably has been damaged if it's not the actual fault.

[Ruger77]

ECM solved the problem. Very low slip RPM's (0-125) with very steady duty cycle & no surging.

[timbre4]

ECM solved the problem. Very low slip RPM's (0-125) with very steady duty cycle & no surging.

Thanks for followthrough on posting solution!

[Ruger77]

Same car, new problem. Installed new PCM and test drove car several times with great success. TCC works great. However, went to back car out of shop next morning.......no start!! I have spark, fuel pressure, crank RPM's on both 3X & 18X sensors, a good Cam sensor waveform at sensor and PCM......but no injector pulse. I have power to injectors, all injectors ohm good individually. Here is the kicker, on my 2009 Modis data stream, I have a line that reads "Cam Sig Present" with a " NO " beside it. To me this would indicate that the PCM is not recognizing the Cam signal. Do I have a bad PCM (It is a Delphi unit from Napa, reflashed by Napa). Also thought maybe Passlock possibly the problem, so I unhooked battery and unhooked PCM for 30 minutes or so, rechecked grounds and Cam sensor wiring, then rehooked PCM and did the 30 minute relearn on the Passlock system. I do not have a Security light on, BCM data shows "Passlock Data Valid" but still no inj. pulse. Also no codes in PCM or BCM. HELP!!! I promised car today, guess I goofed.

[steven kiser]

i would get the original back from napa if possible and throw it in and see what happens. i've had remans that function great and ones that make you want to go to the factory and pop the builder in the mouth. this could be a separate issue in the harness caused when you were moving it around. find the wire for the sensor at the pcm plug and test it there. if it checks out then i'd say the pcm is the problem. if not you have a wiring issue. another tip here use a good tape when you tape the pillow on the wall to cushion the blow to your head. sorry had to say that. i can rarely fit that in.

[Ruger77]

I did check it (Cam sensor signal) at the PCM and I have it there, but it is reading a "NO" on the "Cam Sig Present" line on the datastream. My first thought was wiring also, but I have crank & cam signals going in to PCM, but no inj. pulse out, and a PCM that is not recognizing the cam signal. Seems like I got a lemon of a computer. I'm not sure if I'm missing something?

[Tim Martin]

Interesting. Very interesting.

I use only oem pcm/tcm/vcms. Have had so many problems with others, especially napa.

If the pcm is not the problem, it almost sounds like a wiring issue. Perhaps a poor connection. I think I'd be using my lab scope on the cam/crank sensors and see if that exposes the problem. Just a thought.

[fortknoxx]

can you read the rpms from the scanner? are they reading within normal range? if they are reading low at normal idle. i would check the crank pos sen. if the cps is not sending the right info to the ecm, that might be the problem. i would double check all the sensors before condeming the ecm. have you pulled the cam sen to see if there is debris on it, possible distorting the signal?

[Ruger77]

I have rpm on the scan tool on both crank sensors (3X & 18X) and I scoped the cam sensor right at the PCM and it looks good. I'm preparing to install the old PCM to try that ( had to get it back from Napa). Just for clarification, this is a no-start now, I have everything but inj. pulse. I'll post the results shortly.