Car skips going up hill or under load

Maintenance/Repairs
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I have a 1995 Park Avenue 3.8 with 278,000 miles. Runs fine until about 3rd gear and 55mph when if under any load at all the whole car jumps and shutters. If not under load, like going up-hill, no shutter or skip and runs smooth. If accelerator pressed at all, even when running smooth the shutter begins. Normally does not shutter at lower speeds.

Thought it was the transmission, so serviced the transmission. No improvement.

Took car to local transmission repair. They drove and do not think it is the transmission. They did check pressure at the throttle body, gas flow - let gas flow into clear container, no debris or water - and pressure was in the 52 range. Dropped some on acceleration while in park.

Shop did scan the computer, no codes. Check engine light is not on. Checked fuel filter and it was good.

They also checked all the spark plug wires and indications were that all were firing and in good order. They misted the wires with a spray bottle to see if they could detect electrical leaks - did not find any.

The car is not driven that often and was very low on gas. After leaving the transmission shop, bought gas and initially the car ran great with no hesitation or shutter even at 55mph. Shutter returned within about a mile. The car acts as if it has time to fill a container with gas it runs fine until the container looses some of the gas then it runs rough, or if you are driving along and try to take more than the normal flow out of the container the car runs rough - if they makes any sense.

Bought new gas filler cap just in case. No change.

The fuel filter and fuel pump were replaced at the same time about 2 years ago.

The EGR was replaced about 1 1/2 years ago. New plugs and wires about 1 1/2 years ago.

There is sometimes, but not all the time, a loud pitched whistle which seems to be coming from the area of the gas tank. Oddly enough
if the car is in park and running while the whistle is happening, if the brake is pressed, the whistle changes in pitch to a louder and fuller whistle. When the brake is released, the whistle pitch drops in volume and more of a shrill whistle. Same happens moving transmission from P to R.

I feel I have a fuel problem, however, fuel flow, pressure, etc., seem to be ok. The mechanic drove the car with pressure gauge attached to the throttle body and didn’t seem to feel that the gas was the problem upon returning from the drive.

They had no idea and asked that I leave the car for them to check it. Couldn’t leave it at the time.

Hopefully someone has had this type experience. Even if not, any suggestions or recommendations would be appreciated.

Thanks in advance.

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Skipping under load usually indicates a fuel starvation problem.

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MikeInNH, if the car is in P and at idle and if the fuel flow and pressure at the throttle body is good, and the fuel filter has been checked, would your guess be the fuel pump or is there a sensor or something that could be causing the skipping when car is placed under load? Although failures are always possible, the fuel pump was replaced 2 years ago.

Thanks

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I didn’t see anywhere in your list of parts replaced that you changed the air filter???

I also think the whistling may be a vacuum leak. I’d check all the vacuum hoses for cracks or splits, especially the intale duct from the air filter to the throttle body and the vacuum hose to the brake booster. Sometimes these cracks can be on the bottom side and not easily seen.

These hoses being that old, you are bound to find a few that have weathered and cracked. I’d even think about getting a roll of the appropiate size vavuum hose and replace them all.

Yosemite

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Well, my Riviera with the 3800 was doing the same thing and thought it was the transmission. Turned out to be the crank sensor coming apart. Of course it could be other ignition issues like wires, coil, etc. or gas issues, but the crank sensors are pretty common they tell me on the 3800’s.

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Yosemite, good recommendation on the hoses and I will check that. The whistling is definitely coming from the gas tank area of the car and not toward the front, although it is hard to distinguish the location when the whistle is first heard. Doesn’t whistle all the time, but when it does going from front of the car to the rear the whistle is louder just past the back door.

The air filter is good.

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Bing, when you were having that problem did the car run ok until you put a load on it, for example starting to go up a steep hill or just driving along and start to pass another vehicle, for example. My car is running fine unless I introduce a load - basically having to give it more gas while at a cruising speed.

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My son’s Jeep did the same thing, ran fine until under a load. It has a single ignition coil, replaced that and the problem went away.

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Yep, coming out of St. Paul on 35E, up the long hill from 50 to 65 mph, in high gear, a slight hick up.

Word of warning though, I had just overhauled the transmission so knew it wasn’t that but the shop put 12 volts on the 4th gear solenoid anyway and blew it out for me. A $400 job but covered under warranty. They missed the cracked crank sensor that blew apart the next day causing a $70 tow, $500 repair (with the coming apart balancer) and a day lost. So be insistent that they check the balancer and crank sensor at a decent shop. That was strike three for my shop.

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Remove a spark plug and check the gap dimension. Over-wide spark gaps can cause this. Normally you’d hear some pinging too. But not always. That’s a good time to assess the condition of the spark plug too, for any signs of oil fouling, overheating, etc. If you’re the obsessive type you could remove and check them all, but at this point I’d just remove one and check it.

Also check that the brake booster is holding vacuum like it should. If its diaphragm splits symptoms like this can develop.

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George SanJose, thanks. Very interesting that you mention the brake booster. I mentioned in my original post the whistling noise which changed if I pressed the brake pedal or put the car in reverse. I had no clue that there could be such a connection. I will take your advise.

I am also going to do as Bing suggested and check shaft sensors. For anyone having a similar problem, my next step is to follow the procedures outlined at http://troubleshootmyvehicle.com/gm/3.8L/how-to-test-the-cam-sensor-1 and hopefully determine if a sensor is the problem.

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Crank sensor, not cam sensor, and the rubber cored balancer can come apart and cause a wobble that can throw the crank sensor off.

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Bing, from everything I am reading my car has a cam and crank shaft sensor. For no other reason than I found the cam shaft sensor test procedure first, I am going to test the cam sensor and if it is good I am going to check the crank shaft sensor. The two tests appear to be very similar so it makes checking both at the same time very straight forward.

Yosemite mentioned vacuum hoses and I checked those today. Found one very small one which was definitely cracked. Wrapped it tightly in electrical tape. It helped just a little but did not eliminate the problem.

Thanks, and if I can perform these tests and determine the problem I will definitely post my finding and hopefully someone will be helped in the future.

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It’s gonna be hard for a non mechanic to tell if the balancer is coming apart though and I’m not one.

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I finally found my problem. I do appreciate all the suggestions and recommendations but as it turned out the problem was an ignition coil.

Since someone else might run across the same problem I was having, which in a nutshell was a car that was running fine until put under load, for example, starting to go up a steep hill or merely pressing the accelerator, I am going to give the steps I took to trace down the culprit. Any one of the things I checked could have been the culprit. I found the ignition coil to be the problem and had I done things in the correct order I would have found the problem with little to no effort.

First thing I did was to verify that the cam shaft sensor was working correctly, which it was. This is an excellent document on how to check the cam shaft sensor. http://troubleshootmyvehicle.com/gm/3.8L/how-to-test-the-cam-sensor-1

Both the above cam shaft sensor test and the following crank shaft sensor test require turning the crank shaft manually - not with the starter. Not everyone will have the tools needed to perform these tests - I just happen to have them, not from working on cars but for another reason. The shaft takes a 24mm socket and I think all 24mm are made for 1/2 inch and larger drives. And, if by chance you had to replace the crank shaft sensor, the balance has to be taken off and you will need a 1/2 inch or larger breaker bar or large 1/2 inch or larger rachet.

After checking the cam shaft sensor I checked the crank shaft sensor. The following is excellent documentation on how to check the crank shaft sensor - mine was good. http://troubleshootmyvehicle.com/gm/3.8L/how-to-test-the-crank-sensor-1

The next logical sequence in checking the firing system would be to check the ignition control module.
On this car and many of the 3800 series I (pre-1995) and series II (1995 - ) the ignition control module is separate from the ignition coils (has 3). My ICM was good. This is excellent documentation on how to check the ICM. (They won’t let me put but two links in this post as I am a new user. The same site has documentation on how to check the ICM.)

Within the documentation for the ignition coil pack tests, the author recommends that you have or buy a HEI (high energy ignition) spark tester. Interestingly enough, both AutoZone and Advanced said they did not carry HEI spark testers. The clerk at AutoZone said we do have spark testers, took me to them, and showed me one. One the neck of the spark tester was HEI. They don’t carry it as such in their computers.

I checked each spark plug wire as directed in the documentation with the HEI spark tester and as luck would have it, all wires sparked until I got to the very last one. It did not spark.

Next step is to check the ignition coil to which that spark plug wire goes. Of note is that each ignition coil accommodates two spark plug wires. One wire goes to the front bank of spark plugs and the other to the back bank. Both plugs spark at the same time. Do not make the mistake of assuming that if the plug in one bank sparks that the plug in the other bank will spark. They may not. One of the pair may spark and the other not.

The cylinder which was getting no spark was number 2. I traced the wire to the applicable ignition coil. I removed the spark plug wire from the ignition coil and did as directed in the documentation. I did not get a spark. I then check the other tower of the coil and there was a spark. This meant that 1/2 of the ignition coil was not working.

I replaced the coil and now the car is running like a charm.

As I mentioned earlier, I did things bassackards. Had I started checking the spark from the beginning, which in reality is the smart way to go, I would have spent a whole lot less effort and time.

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Good for you OP for getting your 278K Park Ave running smoothly again. You make a good point when you say checking the easiest and most basic things first is always good plan. But I don’t think the order you chose to test is wrong either. The order of things to test is always a guessing game.

Edit: It’s interesting about the 2 leads from the same coil, one may work while the other doesn’t, thing you discovered. I thought they were actually connected to the same winding, so when one fires the other does too, sicne they are connected together. Just that maybe the other one fires on the exhaust stroke, which doesn’t actually do anything other than reducing the number of coils needed. Maybe in fact they are different windings. Or just maybe still just one winding, but that common connection fails for one of them.

Weird that you got no codes for a miss on the cylinder.

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I ran across the fact that both “towers” in the coil fire at the same time even though only one of the two firing cylinders have gas at the time of the firing. Another thing interesting was that the transmission shop checked all the spark plug wires and said all cylinders were firing - when in fact one was not. That is perhaps why the author of the article insisted that the HEI spark tester be used instead of the old fashion way of just grounding the spark plug in the cylinder hole. When I checked the cylinders with the HEI spark tester all of them except the bad one had very active very visible sparks. The bad one had a very faint spark that happened only sporadically. Guess that is why the shop picked up a spark, it just was not a viable spark.

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I’ll bet you lunch the shop that tested for spark just laid each wire against ground, to check for spark

That is not the proper way, as you now know

A weak and/or failing coil might pass this test, but not pass the test with a proper spark tester

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I wonder if OP did the spark test the way I usually do it would have shown up the problem? I use a spare spark plug gapped correctly for the engine,. I connect it to each wire one by one. I hold the metal base of the spark plug against a chassis ground while cranking, and look for a whitish-blue spark between the spark plug electrodes. If there’s a spark but it is reddish rather than white-blue, that one doesn’t pass.

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Yeah I suppose you have some way to easily ground the plug but I’ve been afraid of getting zapped ever since I was a kid and grabbed the plug wire on my Briggs. I don’t know how to write the feeling with words but it was something like ZZZZZ#@#%. No one heard or saw me but I can still feel it after 50 years.

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