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I recently did an extensive repair on my 2002 Chevy Venture with a 3.4L engine.I replaced head gaskets, intake manifold gaskets, timing chain and sprockets, including the timing gasket. All ignition components, coils plug wires, plugs, etc., are AC Delco original and new. I went into the engine due to the common intake manifold gasket failure and coolant in the oil.
Here are some symptoms of the “soft” misfire that vehicle experiences. I define “soft” as compared to a harder electrical ignition type misfire. I have included some other information that is not symptomatic, but might be pertinent to trouble shooting the issue.
* The vehicle cranks right away and usually runs smooth at first. Sometimes it will miss a bit right after it starts. At other times it runs very well until warmed up.
* After the vehicle warms up, a rhythmic, ‘loping’ idol sometimes occurs. The car never totally dies. The headlights will slightly dim when the loping occurs.
* The vehicle misses intermittently throughout the driving range.
* It seems to run best at sustained speeds/ interstate, etc.
* The vehicle occasionally stutters at take off in traffic.
* no check engine light has come on.
* vehicle has not totally stalled out.
Any ideas/ trouble shooing pointers would be helpful. I have checked all ground wires. They seems to be tight and in good order.
Thanks much
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WELL THE MYSTERY OIL IS GOOD BUT I NO YOU HAD SAID THAT THE HEADS WERE CHECKED OUT WIN YOU HAD THEM OFF. SO YOU CAN MOST LIKELY RULE THEM OUT I DO HAVE 5 GAL OF GAS IF YOU HAVE A LIGHTER LOL. BUT TELL YOUR FRIEND TO LOOK AT THE O2 READINGS AND LET US NO WHAT EACH ONE OF THEM ARE YOU MAY HAVE A VAC LEAK THAT IS JUST ENOUGH TO CAUSE THE SKIP, YOU DID HAVE EVERY THING ON THE TOP OF THIS ENGINE OFF SO THIS MAYBE THE PROBLEM.BECAUSE IT SOUNDS LIKE SECONDARY IGNITION IS FINE IF HE HAS DONE ALL OF THAT. I HAVE PUT ENGINES BACK TOGETHER AND SOMETHING NOT SEAT RIGHT AND IT CAUSE A SKIP AND COULD NOT FIND THE LEAK WITH SPRAY.MAYBE THIS WILL HELP.
Being a factory technician, you have options to call factory Tech assistance when you have diagnosis issues. After a compression reading was low, but still at specs on the cylinder that was misfiring only at engine idle rpm’s Tech assistance told me, “they had other cases with the piston rods being bent on 3.1L engines”. I remove the engine cylinder head and found the piston was below the cylinder block deck at TDC.
A few weeks later another Tech in the shop had the same issue and found the same thing on a different cylinder.
We could not find any evidence of water or anything else that would have caused a bent rod.
I never did recommend or use additives, but I have friends that use Lucas (SP) products and swear by it.
If your friend finds the problem, please post it. Good luck.
Hamby’s Auto, I quite literally laughed out loud at the 5 gallons of gas reference. As a former insurance adjuster, the stories I could tell…Once a fellow adjuster adjusted a claim on a burned out vehicle on the side of the road.A pretty young lady even cried at the scene on his shoulder. Later he discovered the car was missing the front axles and transmission…haha..I digress…
When I got the heads back from the machine shop, I did install new valve seals on my bench. The bottoms of the valves (combustion chamber side) looked very clean. There was, however, some carbon on the stems…not excessive. I will keep you all up to date. As long as this post is getting, Eric will need to start charging me for space on the forum :)Thanks for the continued interest and helpful advice…
LOL. MAYBE HE WILL GIVE YOU THE LOYAL CUSTERMER DISCOUNT WRIGHT. WELL LET US NO WHAT U FIND OUT. I REALY WANT TO NO.
Post all you like, no charge. That said, there is only one way a connecting rod can get bent and that’s hydrostatic lock. Either a cylinder gets filled with fuel or water and the piston comes up and the rod gets bent. There really is no other way for it to happen outside of poor installation. That said, have you run through water recently or had a cylinder fill up with fuel? If the answer is ‘no’ to both, then I would look elsewhere. Your compression numbers are low and don’t look great. They’re not bad, but not great either. Especially on cylinders #1 and #5. If I’m not mistaken this engine uses a timing chain. It might be time to look into a possible issue with timing chain slack. This can offset the mechanical timing as well as the ignition timing. I’m not sure how to do it on an engine without a distributor though. That might be a bit tricky. I’m hoping you can check it without removing the timing cover. You might be able to remove the plug from where the distributor used to be (if you have one) and observe the cam as you rotate the engine counterclockwise. If it takes some time for the cam to start rotating, it could mean you have excessive timing chain slack. I have a video on this showing how to check slack with a distributor car that should be coming out in the next couple of months. Sorry I can’t help you with that now. A more detailed explanation of the process can be found here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted and don’t worry about how much you post. That’s what we’re here for.
Thanks much Eric; I did notice that my post was much longer than most. I appreciate the freedom to keep going. I wouldn’t rule anything out as this point, but when I did the work back in January, I replaced the timing chain and sprockets. The new one had less slack than the old and lined up nicely. I’ll see what my mechanic friend finds out soon. I’ll be sure to post it. Also, I’ll pass along you suggestion here. The timing chain cover is unfortunately sealed as it does not utilize a distributor. Thanks for your interest. I have an Aunt who lives in Adams county Ohio, not far from you. She owns a huge farm…would love to come to the “meet up” in July sometime…
Hi Eric,
I had a question for you about tomatofarmer1’s Lumina. You were saying that his compression is low, especially for #1 and #5. How do you determine this as I would say #2 and #6 as the wet compression is somewhat lower than the others. All are within 15% and I thought that was what is perfectly good. Also, I know all cars are different so how does one determine what is normal outside the FSM?
Sidenote for tomatofarmer1. My brothers Equinox was having misfire issues and only throwing the P030X code (it did keep changing cylinders). After a lengthy stay at the dealer, they decided a leakdown test was in order and found for someone reason the catalytic converter was bad. Replaced it and all has been good since. Probably not your issue, but what we learned is misfires come from anywhere! Good luck finding yours.
If you’ve already replaced the timing chain I think we can table that theory. Now I’m beginning to wonder if you have cam lobes that are worn or something like that.
Never rule out mechanical. It’s so often overlooked but is the most important thing when it comes to engine performance. If you don’t have solid mechanical, you don’t have a good running engine.
Please continue to keep us updated.
[quote=”KingMeander” post=96152]Hi Eric,
I had a question for you about tomatofarmer1’s Lumina. You were saying that his compression is low, especially for #1 and #5. How do you determine this as I would say #2 and #6 as the wet compression is somewhat lower than the others. All are within 15% and I thought that was what is perfectly good. Also, I know all cars are different so how does one determine what is normal outside the FSM?
Sidenote for tomatofarmer1. My brothers Equinox was having misfire issues and only throwing the P030X code (it did keep changing cylinders). After a lengthy stay at the dealer, they decided a leakdown test was in order and found for someone reason the catalytic converter was bad. Replaced it and all has been good since. Probably not your issue, but what we learned is misfires come from anywhere! Good luck finding yours.[/quote]
Compression can be in spec, but if it’s not even across all cylinders the engine cannot run smoothly. A good running engine is balanced. If there’s enough of a discrepancy between cylinders, it will run run smoothly and you will likely get misfires and performance issues.
yes i have had engines that have had very low compression. but each cylinder was the same or real close. and they ran very well not a lot of power but ran smoothed.
I respect and appreciate everything you guys share from your wealth of experience. While I would rule nothing out, this misfire was not present until after I went into the engine due to the common intake manifold gasket issue. My first post summarizes what I did in January. So if it is mechanical, it’s likely something I caused during the repairs. This one may truly remain a “mystery misfire” until the end…
hi i got some questions for ya maybe you have already answered some of these but this is a REALLY long post, id like too give this a shot please excuse me if i have already covered anything you already have…
i did see the compression numbers but i don’t think they are bad enough too cause a miss like you are experiencing and i did read the timing chain was replaced… odd compression numbers are not un common due too the fact these engines 3100 and 3400SFI are know for piston slap after so many miles making a ticking noise until the engine warms up due too odd wear with the pistons causing excessive clearences, after a while it wears down on the pistons more you loose some more compression if the engine makes a ticking noise this may be why the compression numbers are the way they are but i would not be alarmed.
another issue that is quite common for these GM engines like the 3400 is a lack of fuel pressure, the fuel pump can start too wear out and fuel pressure lacks causing a lean condition, if your engine is running lean it could very well be a fuel pump issue, fuel pressure should be between 40-50PSI and the area too test fuel pressure is on the fuel rail i believe there is a place too screw a fuel pressure gauge down close too the fuel rail… if you can do a fuel pressure test, below that i would suspect a fuel pump or maybe a clogged fuel filter if your fuel gauge is really wavy and doesn’t read fuel level it could be a indication that the fuel pump may be doing itself in
sometimes the ignition systems get picky on these cars, its best too run AC Delco plugs NGK V power works really good too! recommended running AC Delco wires BWD wires work good too… once had a 3400 in a pontiac grand am come in the shop with a really bad missfire one of the plugs oddly enough was badly cross threaded and had a missfire, but i don’t think you are experiencing this issue… sometimes Bosch plugs cause drivability issues or even Autolights sometimes but not often, my grandpa put Bosh plugs in his century they ran just fine then i replaced them with NGKs later on they ran a little better.
i have not heard much at all about valve timing issues on these engines other than the rocker arms can get stripped from time too time, since the lifters are roller style it doesn’t quite chew up the cam lobes quite as easily unless for some really wonky reason a roller got stuck, my suggestion there is pop off the rocker covers and make sure the rocker arms are nice and snug and none of them are loose, if any of them are loose they may not be opening the valves properly this may cause a lack of airflow too a cylinder and cause missfires, but typically when a rocker arm strips a bad clattering sound is emitted which may be masked if the engine does have piston slap…
if you can get some missfire data and if a pair of cylinders sharing the same ignition coil are missfiring the most try swapping ignition coils and taking it for a drive again and see if missfire data changes too different cylinders if so a ignition coil may be weak.
as far as products like Seafoam and marvel mistery oil, my suggestion is too use with caution because thye can cause issues if not used as directed, we used Seafoam quite a bit when i worked at stap brothers if the fuel injectors got sticky or gummed up it worked sometimes but not always, and if you don’t use it as directed you can ruin a fuel pump! follow the directions on the can and use at your own risk!
Hi 13aceofspades13,
I thought I would address a couple of your questions as this post really is long. Maybe I can summarize so future viewers can be spared the pain of reading my small novel here.
Back in January, due to the common issue of coolant in the oil, I went into the engine. The following items were addressed/fixed: timing chain and sprockets, new harmonic balancer, head gaskets, heads pressure tested at machine shop, valve seals replaced, intake manifold gaskets replaced.
After the repair, I had a combination of issues, including a loping idle and misfires on a few cylinders. Some improvement was made by addressing unmetered air issues in the intake and changing the o-rings on the fuel rail and injectors.
After all vacuum related issues were addressed, I still have a misfire on cylinder number 2. This has been present since the repairs were made, but not before.
The engine only once threw a code, P0336. The following has been addressed. The 24x and 7x crankshaft sensors were replaced as well as the camshaft position sensor (all AC Delco OEM). The spark plugs have been replaced with AC Delco iridium plugs.
To address the possible misfire cause(s) in this cylinder, the fuel filter, spark plug, spark plug wire, coil and ignition control module have all been tested (either replaced or temporarily swapped out). The misfire is still present.
The vehicle is now with a very good mechanic friend for further trouble shooting. I offered your suggestion about the possible demise of the fuel pump. He disagreed, saying that if that were the case, it would likely show up in more than one cylinder. Thanks much for your interest and input. I’ll wait until I have some more solid information before updating my post again.
Keep us updated on what your friend finds. Sometimes it’s nice to get a fresh set of eyes on something.
It’s been a while since I updated this post. The car was at my friend’s shop for several weeks as he did some trouble shooting between paying jobs. He finally exhausted his efforts trying to find the misfire and turned it back over to me. I’m happy to report the mystery misfire is fixed!!!! I discovered the problem was caused by an after market harmonic balancer. Hallelujah!!! I made a Youtube video to help anyone else who may encounter this issue and P0336 DTC code. I’ve attached it below. Thanks to Eric and all of you who offered support and advice as to potential causes. I received much encouragement and learned through this process. Take a couple minutes to check out my video…not much to watch, but hopefully it will help someone who faced a similar challenge.
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