Engine bucks (misfires)

[Johnnywiffer]

I'm having a real problem with the '96 Olds van I got recently.

SOMETHING makes it buck. It only seems to happen when I'm going level or downhill. If I'm going slightly uphill or accelerating, it doesn't seem to happen. Or at least not as much. And it doesn't happen until the engine is warmed up. In other words, I can drive maybe 4-5 miles before it starts to happen. It actually began doing it when I was bringing the car home—but only after 2-3 hours of 70mph driving.

That made me think it was something in the gas—maybe water. A while back, I put in a bottle of Heet”, which is mostly ethyl alcohol. And it seemed to go away or only happen later in my drive time than it had previously. Then it began happening more and more. So I put in 3 bottles of “Heet” (“If a little helps, a lot will....” (You know the saying.) But now it bucks MUCH more and sooner than previously. Sometimes it will die at a stop light but so far, has always started right back up.

I'm thinking it is not the electrical system because accelerating seems to help, tho not always.

Does ANYONE have any ideas?

John

[41 Frank]

Lots of possibilities here John. Bad spark plugs,dirty injectors,bad MAF (mass air flow sensor) Does the "check engine light" come on?

[Jim B PEI]

Wild guess. Something like the 'coasting' valve/circuit?

[Johnnywiffer]

The "check engine" light is on but as for bad spark plugs or dirty injectors, it accelerates very well. usually without misfiring. In my opinion, when the goop in the gas tank (if there is any) gets up around the fuel pump intake (in the front of the tank) when I decelerate or just drive on level ground, the car misfires.

When I accelerate or go up hill, it SOMETIMES will mis-fire but usually doesn't. It has never failed to start easily when it (infrequently) dies at stop lights. The tank is about half full but I'm thinking about jacking up the car, so whatever may be in it runs to one corner of the tank, then boring a hole in that corner of the tank (it's plastic) and seeing what runs out. Then put a screw in the hole and seal it with J&B Weld.

As for the check engine light, I have not checked the codes because from the 1995 model on, it requires a reader, not a paper clip. And I have put off paying $60 just to be told my gas tank has some crud in it. (In the dictionary, next to "CASO" is a picture of ME!)

John

[Bob Andrews]

Just went through this exact issue with my 02 Rendezvous with basically the same engine.

I was sure it was a coil pack, since it ran perfect until it was FULLY warmed up- like 10 miles or more, and then only under load; classic failing coil. SOLUS said cyl. 4. Injector tested fine. We put on a known good coil pack- did not solve it. My techs were stumped.

Solution was to get with one of our "contacts"- a brilliant young kid that's a GM tech, and does troubleshooting on the side as well. He took the car home and brought it back fixed the next day! (Smart-aleck kids<G>). Where we have a $5K SOLUS, which diagnoses all makes, he has a $25K GM-specific machine; tests every wire and coil separately, even runs each injector individually. Turned out my problem was a corroded wire going to injector #4 (!). Was fairly easy to track down with that equipment.

Here's something we have found: When doing diagnostic work, it is common for techs to check wires for power with a test prod. GM does not recommend this, because by probing a wire you create a pinhole in the wire insulation. While it doesn't seem possible, moisture can wick into that hole and can cause corrosion and failure of wires and connections. That's what our GM tech said happened in my case! Has run perfectly since his repair.

So if your car was mine, I would suspect plugs/wires, coil or coils, then finally fuel. Could be any of these. Ultimately, quality diagnostic is the key. That, or throwing parts at it Most of the time, it's cheaper to pop for the diagnostic- at a shop you KNOW is honest.

Let us know the resolution.

[Packard53]

I had a problem with my 2006 HHR and took it the mechanic I have been going to for 25 years he worked on my car for two days trying to find out what the problem was using his five year old diagnostic computer equipment. Turns out he couldn't find the problem and I took the HHR to another mechanic who had up date equipment. It took them about an hour to find the problem which turned out be leaking sealing o-rings on two of the fuel injectors and an other two hours to fix the problem. Now the new mechanic is getting most of my business because he has up to date computer equipment to do the diagnostics.

John S.

[Johnnywiffer]

OK, guys, looks like it's off to the shop for a diag. I'd sure hate to drill a hole in the gas tank only to find it was the coil or a wire or whatever. I truly appreciate the help.

John

[fargoguy]

I think that some of those GM V6s had trouble with intake manifold leaks- maybe a small leak once it warms up causing misfire in one or two cylinders?

[Johnnywiffer]

The lower intake manifold gasket disintegrates after a time on those engines but my experience has been that it usually lets water into the oil, not leak air. Of course with GM engines anything is possible.

I had 2 '96 Pontiac vans with the 'water-in-the-oil' prob. Cost about $600 to repair each. The service writer at one place told me that there was a national back order (at the time, about 5-6 years ago) on those gaskets because of the problem. A service writer at another shop said he could make a living JUST fixing those engines and showed me the broken gasket from mine.

And that prob wasn't just in the '96s. It continued past the 2000 models on the 3400 engines. GM never admitted any fault in the engines.

John

[Johnnywiffer]

Finally took the van to O'Reilly's to have the codes read. There was only one. Said something like "bad cat". I've had a car with a stopped up cat. It would barely go 20 mph. Of course, maybe the "bad cat" is caused by the bucking.

A guy on the Olds Forum suggested a bad ground somewhere, aggravated by the engine warming up. Or a bad fusible link. Where the heck are THEY?

It looks like my $400 van is gonna cost more.

John

[Bob Andrews]

Still recommend your plan in post #7.

[bige]

These engines don't react to bad plugs the way the old ones would. They can feel OK with HUGE plug gaps and worn electrodes. Coils, plug wires and plugs are most common causes and since it doesn't require a load to act up it I'd guess wires or coil first but it doesn't make sense not to do the plugs.

ErnieR

[Nelsen Motorsports]

My Eagle misfired at low rpms, but ran good above 1,500 and this was due to old plugs.

[Johnnywiffer]

Mine is just the opposite. It idles OK and accerates well, just bucks mostly when on a level or doing down hill. On slight incline or accelerating, it's pretty much OK. I'm really leaning toward checking all the grounds I can find tomorrow.

One guy on the Olds Forum had a similar prob, with a thread that took up 5 pages, detailing changing just about everything imaginable. But his had MAAAANY probs--beside bucking and stalling, the side door wouldn't open automatically, instruments went crazy, radio worked only sometimes. Really a very long tale of woe. Finally found it was a BUNCH of shorts where a wire group rubbed on the AC drier. I'm checking for that kind of thing too.

But I do appreciate all the help from here. I just don't want a $400 car to turn into an $800 disaster.

John

[Johnnywiffer]

Learned something interesting today. Since we got it home, I had never driven the van much. Usually my wife would and it didn't buck until she got home or near home from work.

However, today I drove it and I noticed that once the engine revs to 4000 rpm, it will not go higher AND if you hold it at 4000, the tach goes back and forth from 4000 to 3800. I held it wide open for maybe 10 seconds and that's what it did--never above 4000 or below 3800.

Does that sound like ignition or cat? Or both?

John