Chugging while accelerating on hills

[Ken_W]

I brought this up a few weeks ago, but the thread fizzled quickly. Maybe if I present things differently I'll have more luck...

My SSEi (other than its current rear suspension problem) drives smoothly 97% of the time. When going up gentle hills on the interstate (around 45-60mph), however, it starts "chugging" (probably not the best term). It seems like somebody is putting their foot on and off of the gas pedal, maybe five times every three seconds. RPM's stay constant and the car makes no noticible noises. The car does not speed up or slow down; it just seems like it is struggling in an on-and-off fashion.

So far I have checked the tops of my ignition coils; they were 6.7, 6.8, and 6.7. I know I could remove them and check the bottoms, and take the ICM to Auto/Zone and have that checked, but since the car runs fine 97% of the time I have a feeling that the problem lies elsewhere. Could this be the early stages of my cat failing? What else could I check?

Ken_W

[Ken_W]

Other info:

Ran one hour last week with disconnected MAF sensor. Still had the chugging on hills. Interestingly, did not trigger Check Engine light. Went to Advance Auto and had them scan for OBDII and ABS codes, only history code found was B1287 "Steering Sensor Excessive Rate / Wiper Offset Malfunction" which I take to mean I need a new SWPS. (My "Service Stability System" light comes on every now and then, and then goes back off.) This, however, is probably unrelated to the chugging.

Other info: (to rule some things out)

- Replaced spark plugs (NKG TR55 V-Power copper), wires (AC Delco), PCV valve, fuel filter, air filter, and front O-2 sensor (Denso) ten months / 12K miles ago.

- Cleaned MAF sensor and throttle body a couple months later, and also have run Seafoam and Techron through fuel a couple times since then.

- Checked fuel pressure 5 months ago, it was fine. Checked fuel pressure regulator and it seemed okay.

- Rubber fittings on vacuum lines starting to crack but seem to still be doing their jobs.

What else should I check?

Ken_W

[Archon]

Replace any of the vacuum lines that have cracks, and check the others closely. In particular the "T" from the LIM under the supercharger snout. Intake gaskets ever replaced?

[Ken_W]

I will replace the vacuum T as you suggest, just to rule that out (if not get lucky and solve the chugging problem). I already had my eye on the GM "vacuum harness" that contains this T along with a couple other rubber fittings. Should I go ahead and get that, or is there an easier, cheaper way to get the same result? Does somebody make compatible/universal aftermarket fittings?

I have not replaced the intake gaskets yet. (That's the only thing on the Club's 3800 Maintenance List that I've yet to complete.) The LIM gasket that is in there is black, but may not be original. I've owned the car for 11 months (purchased at 150K, now at 168K). I watch the coolant level closely, and check the oil for signs of coolant, and so far I have seen no signs of trouble.

Now that you mention it, however, I did a coolant flush nine weeks ago (at home, using Techinfo procedure), and this chugging problem started about 3-4 weeks after that.

Ken_W

[00Beast]

There are no aftermarket fittings, you can make them with vac line and plastic vacuum t's, but it's just not worth the hassle. The vac harness is like $26 at your dealer.

[swampthing]

See if you can find a mother set of coils to check, when I first had this problem after chasing a misfire a new set of coils took care of it even though all 3 were within spec when tested

EDIT: I meant another set not a Mother set, that's what I get for typing in a hurry lol!

[Bing]

I would try the vacuum harness first just to rule that out of the possibilities and then go from there.

This is fairly cheap and it sounds like it needs to be done anyway.

[00Beast]

I concur with a possible bad coil. I'd swap them out with a set from the JY.

[Ken_W]

Vacuum harness has been ordered. Should get here later this week. The price has risen on those things, up to over $40 shipped. They were $26 plus shipping a year ago; now they're up to around $32 plus shipping. I guess the prices go up as inventory dwindles. The part number is 24508742, for anyone who may be thinking about getting one.

As for coils; could I just get one new coil and systematically rotate it through the three positions one-by-one (seeing if it makes a difference), or it is better to have all three coils be the same age? Only one of my current coils still has the original white numbering on top, so apparently the other two were already replaced at some point.

Ken_W

[01bonneSC]

Im leaning to torque converter not coming out of lockup.

[00Beast]

I'm leaning that way.

Just get a junkyard coil and swap it around, or get all 3. Doesn't matter. Don't spring for a new one, not worth the cost...

[Ken_W]

I finally installed the new vacuum harness yesterday. Took it for a test drive on back roads. Was not able to get it to chug. Took it for a short 20 minute freeway test drive today -- still no chugging.

So; I'll continue to watch it. Perhaps the right conditions have not yet occurred, or perhaps it is fixed. Will post an update later this week.

Ken_W

[jedwards83]

My car does the same thing while going up hills with the torque converter locked. These cars like to hang onto high gears for economy reasons, and usually once I give it enough gas to get into boost it starts chugging.

I think it's ignition related. It got pretty bad once and I replaced the plugs and it was a lot better afterward. There was an even bigger improvement when I ditched the TR55 plugs for an Autolite 104 equivalent. The TR55's protrude a lot farther into the combustion chamber when compared to my current plugs side by side.

[wjcollier07]

Is transmission maintenance 100% up to date? It could be the transmission slipping under load and causing a shudder that is translated to you as a chug. Maybe do a drain, filter and fill with Lucas trans fix along with your normal trans fluid just to fill another void of possibility. Obviously its more likely a coil though. I'd grab a junkyard set and swap em over quick just to compare.

[00Beast]

He just had the trans partially rebuilt, John.

I believe he's swapped coils too.

[wjcollier07]

I didn't see anything about swapping coils...but I did miss the part about the vacuum harness possibly solving the problem. Also didn't know about the trans.

Hope that fixed it for yah!

[Ken_W]

I have a set of used coils (from Beast00's first Bonne, which apparently got totalled), have not put them in yet. I've been wanting to see if the vacuum harness would fix it first.

Have not been driving the car for the last several days. Took it to my mechanic to get rear suspension components replaced, and have not gotten it back yet. On my way there, however, I did get a reduced chug at one point (less than before, but still there). So -- not cured yet. I'll swap out the coils when I get it back, which will hopefully be tomorrow.

As Beast mentioned, the tranny was partially rebuilt 10 months ago and refilled with DexVI (synthetic).

Ken_W

[01bonneSC]

What all got replaced your partial rebuild?

[Ken_W]

I will dig up my receipt and list the parts that were replaced in my trans later. Unfortunately transmission stuff is all greek to me, so I cannot list the replacements from memory.

I've been driving the car for a couple days now, and it is definitely better. Instead of chugging 4-5 times each way on my one-hour commute, it only chugs 0-1 times, and when it does chug it is in a smoother way, less abrupt than before. I'm wondering if I should replace other vacuum components, like that cap that covers a stub and commonly gets cracked with age? (on top of engine, near throttle body) Mine has a bunch of micro-cracks. Are there other vacuum areas that commonly rot out with age?

I'll also start experimenting with ignition coil swap-outs also, as discussed above in prior posts.

Ken_W

[Ken_W]

Some new information that may aid in diagnosis:

I had long suspected that humidity played a role in this. It seemed like it got worse on highly-humid days, or in the rain, but I was never really sure. Since it had been running pretty well lately, I was actually looking forward to the rain that began on my way home from getting new tires today. It ran great on my way to the tire shop -- no chugging whatsoever on the 30-minute trip. At this point, however, it had not rained in over a week.

Afterwards -- sure enough -- it was raining and the chugging problem was back with a vengeance. It most certainly gets worse in the rain. It remains, however, less severe (when it occurs) since I replaced the vacuum harness.

Does this clue help anybody to ID the problem?

[Edit: have still not yet swapped coils.]

Ken_W