intermittent highway hiccup

Three very slight problems that may be related.

1) Every now and then when I am cruising at 75mph the car just has a very slight loss of power for a fraction of a second. No sound to go with it or change in the tach or anything.

2) When starting, it seems to take an extra fraction of a second to start. In the last month I have let go of the key and the engine hadn't started.

Now these are pretty insignificant and a lot of people may not even notice them. My car has over 208,000 miles and 175,000 were put on by me so I have a lot of history with what this car should feel like. Also, with that kind of mileage, a lot of things could be going wrong.

3) The SES light came on for one day. After several trips it went out. It isn't the bulb because that still lights when starting.

No mods, just miles. Any ideas?

might want to scan it to see if you got a code stored, might tell you what triggered it and you can start from there.

I'm thinking it's something fuel related.. maybe a funky injector or water in the fuel?

Check spark plugs and wires. How many miles are on each?

i'm thinking wires and plugs, cause mine did the same thing. pull off the first 3 set of wires and inspect the wires.

I would also start with wires and plugs.

The computer saves codes in it's history. Autozone can read the codes and history, see what codes were there.

First thing to do is find out the code. Then if the plugs and wires are old or a visual inspection shows a fault, I'd replace them.

Might be that fuel pressure isn't what it used to be, when you start... try this, turn the key to on, wait 3 seconds and then crank.

This exact same thing happened to me. Here is my view of what to do.

First, try to relax. The big problem with intermittent car problems is getting the car to act up in the first place.

The SES light coming on then going back off should leave a code in memory. Get it read. If you don't have a code reader, AutoZone will pull the codes for free. Or you could buy a code reader. I use car-code by Alex Peper.

If that code is related to fuel, odds are it's the fuel pump. To verify that you need to go to a dealership and have them use a Tech II to command the pump on and off and listen to it work. A tech should be able to get the pump to act up if it is the problem. If you can, buy a Bosch to replace it, the OEM ones are OK but the fuel level sensors are not accurate over time. I think PartsAmerica.com has the Bosch pumps. The cheap way out is to buy a used fuel pump from Ed Morad (run search on this site to find his address/phone).

Now - more thinking. When your car won't run intermittently, or has 'loss of power for a fraction of a second' most likely the problem is spark or fuel interruption. Compression is the only other reason it would not start and run - and if it runs nice some of the time then compression problem is unlikely. Really, really unlikely.

However, we have to find the root cause of *your* problem.

The Riv uses a timing chain, so there's little chance your engine has jumped time even with the 200K miles.

When the Riv ignition is turned on, the computer closes the fuel pump relay. You can hear this--on a cold start (in a quiet place) turn the ignition key from 'off' to 'run' (not all the way to start) and you will hear the fuel pump whirr and maybe even hear the injectors spritz. (if you *don't hear those, better fix the fuel pump and/or relay). If the relay does not close, the pump gets no power and does not run. If the relay is weak or contacts are going bad, it will open once in a while and let the fuel pump stop and it may sound weak or wobbly during that start sequence. But with a weak pump and/or relay it is sometimes the case that a little vibration from rolling along, the relay closes, the pump re-engages, and wha-la you are running again. And d*mn near clueless as to what's wrong, because everything looks and tests normal. So you may want to check the fuel pump relay - and actually they last a long time but not forever, consider replacing it anyway. Checking the pump involves taking a pressure reading at the Schrader valve on the fuel rail in the engine compartment. I do not know the values, and I do not remember if there is a sensor that will let you read the pressure using Car-Code - there may be.

Anyway... If you do nothing, eventually (a couple weeks to a couple months) the car will have highway hiccups more often and then fail to start or stop running. If this happens, you can then use a spark plug tester (basically a spark plug with the side electrode cut off and a ground clip to attach to the engine) - pull the #1 wire off the plug, attach the tester, and crank the car. If you have no spark, you have found a problem.

I bet that as it is now, if you drive it (especially stop-and-go continuously on a hot day) for about an hour and park it for 15-20 minutes, try to start it and it won't start, OR if after driving for an hour or two it gets 'hiccups' the problem is most likely the crank sensor.

You can confirm it this way:

- test resistance across each coil, you have 3, to see if they are all in spec
- when it won't start, check (electrically) an injector to see if the engine computer is sending out pulses. If not, that tells you the computer is not getting a crank signal (assuming it's good, which it probably is) and you thus either have a broken wire, dead computer, or a punk crank sensor. So here's the rub. If the engine computer gets no signal from the crank sensor while starting, you'd think it should set a code. But it does not - at least not on the Riv. One of the mechanics at Fox Auto (local Buick dealer) explained to me that the crank sensor is not checked early enough in the start sequence to even set a code if it is bad. Rather, if there is no crank sensor code, the start sequence will not finish because if there is no signal from the crank sensor, the engine computer won't trigger the coils (via ignition computer) or the fuel injectors, therefore the engine won't start or run. And if the crank sensor fails while running, I am told that to the Riv's engine computer it looks like you turned the car off. So no code is set.

If there is any good news here, it is that the crank sensor is the only component that I know of that will reliably cause the pattern of failure you are seeing. And it's not real expensive. Rockauto.com shows them for $25 to $30.

All that said - I also learned from the mechanic that the crank sensors tend to go due to time and/or mileage. With 9 model years and over 200,000 miles, bub, you are definitely due.

I have to run - hope this explanation helps you even though it's not complete. Search the web for "3800 crank sensor problem" adn you'll find much more about this.

Albertj

PS - A crank sensor is a Hall Effect sensor (if you are curious, search "how a Hall sensor works" on the web). It has no moving parts, but when it is near end-of-life its internal resistance goes to infinity when it is heat soaked, and returns to normal when it cools. So when the engine is cool, you can't find any problem. And the way the engine controls are programmed, no code will be set. And when it is warm, the problem appears when the crank sensor is heat soaked and goes away if you open the hood and let it cool off. Get the picture? the thing will quit on the highway, and by the time you get hooked up and towed to a repair facility it may well have cooled off and everything will work again. Eventually it will quit and stay quitted. After stranding you more than once.

PPS - do NOT be surprised if you have a fuel failure (the pump or the relay or both) *and* this crank sensor failure at the same time. At your mileage, those components are past the end of their design lifetime (which I was told is 150-ish thousand miles).

Thanks for the ideas. The code went out after one day?!?!?!?!. It has been 60,000 miles and about 18 months since plugs, wires and fuel filter were done. While traveling home yesterday it got a bad case of the hiccups. the hiccup still lasts for only a fraction of a second but I had more of them. Dropped the car off at the shop last night. I may have them do all of the above. For me this would be less painful than being stranded. Unless I got stranded next to a golf course!

Wires and/or Plugs. Check them all again. Sounds exactly like the problem I had with a cracked plug. Runs fine most of the time until the heaviest load (torque converter locked up cruising), then kicks at you from time to time.

What happens when you push the throttle to the floor? A shudder at WOT would reveal a faulty plug or bad wire. Keep in mind that a wire can look perfectly fine to the eye, and work great under normal driving conditions, but when the PCM switches to the spark map for boost, it may not be able to take the extra voltage demand. I thought my transmission was falling apart once... it was only a bad ignition wire.

UPDATE The code was still in memory. "FUEL TRIM" The fuel filter was clogged. Since the car also just went over 209,000 miles I had the fuel pump replaced as well.

I was told that a FUEL TRIM code can be set when the engine is running lean. To answer the post above, acceleration at WOT has seemed a little more sluggish lately. Could this be the lean condition is causing the engine to call for more KR?

I have not had a chance to drive it much to see if this will cure everything. I really appreciate all the ideas. I will probably have the crank sensor replaced as well as the plugs and wires done as soon as I can. The plugs and wires have 50,000 miles on them but I can actually do this myself.

If you don't have other mods, the factory plugs are good, no kidding, for around 100,000 miles. More highway service = longer plug service becuse the plugs do less duty. In general it takes that long, 100K, for the gap to creep beyond factory spec. If something else goes wrong (craked insulator or what have you) then gota react to the problem, naturally... Factory wires are pretty good too, one of mine quit after about 80 or 90,000 though, and took a coil with it.

Albertj

If the fuel filter was clogged, you almost certainly were running lean. This condition actually causes knock because fuel delivery is hampered, so your A/F ratio is skewed. Your KR was probably through the roof!

When I hit the road again on monday I will be looking forward to the acceleration again.

AA wrote:

I thought my transmission was falling apart once... it was only a bad ignition wire.

yea, the transmission was later sorry, I had to AA.

I got 110K on my stock plug wires - I think Im nearing a record.

I was at exactly 110k when my wire went! Drive carefully...