Crysler voyager -95 3.3l Backfiring in aircleaner ,New info!!

Hey Janne,

What you have described so far isn't possible. Here's what I'm hearing you say:

1) Backfiring at part throttle, not full throttle. 2) Ignition system completely checked out with a friend's scope and timing is correct and all parts of ignition system have been replaced 3) Car completely within emissions.

In short, this isn't possible.

So, let's go back to the beginning and start over.

If this was a spark plug/secondary ignition problem (bad coil, crossed wires, etc.) then the misfiring/backfiring would get worse the higher the rpm.

If this was a spark primary ignition problem (ie: timing) then the friend and his scope would have caught it.

If this was a restricted fuel filter or bad fuel pump then the higher the rpm the worse the problem.

If this was a compression problem it wouldn't be backfiring.

If this was a fuel problem then the emissions would be out of wack.

So I have to conclude that your testing methodology is flawed. If you are absolutely positively positive that the timing is perfect and the ignition system is perfect - which means your friend and his scope tested it out correctly - then the problem is in the fuel system, specifically the engine is running too lean - which means that the HC would be high and the CO way low - which means the emissions would be off.

In short, you cannot have it both ways. You cannot have a perfect emissions report AND a perfect checkout with your friend and his scope, and still have this problem. One of them has to be wrong.

Off the cuff the most likely candidate is bad timing at part throttle, OR too lean condition at part throttle. However both the timing and the mixture are computer controlled. There is an old saying with computers, garbage-in, garbage-out. I think the likeliest problem here is you have one or more bad sensors feeding into the computer.

The fact as you say that sometimes it runs fine is even more an indication that it's a sensor-to-computer problem. Maybe a bad sensor that with the vibration occasionally "heals"

Some would say that if it's a bad sensor that the computer would set a code. Well I have a '95 T&C with a 3.8 and when I bought it 3 years ago used, the EGR valve was shot, and the van wouldn't pass emissions, and there was NO CODE set. PERIOD. Replacing the EGR valve dropped the NoX down and it passed emissions. So don't argue with me and tell me that the computer in these things is smart enough to detect if a sensor is shot. I know from experience this is just wishful thinking. Sometimes sensors will fail in such a way that the computer cannot figure out that they are bad. For example, your TPS could have worn out the middle of it's slide and the computer not know where the throttle is, fuel mix is going to be wrong, then. Car computers are notorious for saying one part is bad when it's another part entirely.

You say you have already shotgun the ignition system components. Well fine, great, quite replacing them. Or better yet keep replacing them and send me your old ones because they aren't broken.

It's time you put a scan tool on this vehicle, or pay someone to do it. If you really want to do it yourself, you can buy an OTC Monitor 4000E off Ebay pretty cheap that will do this. You need to scan it and run the engine and make sure your actually getting valid inputs from all the sensors. You need to check timing with a timing light - yes I know the factory manual says timing is non-adjustable, but a timing light and degree wheel on the crank still work. The cam chain could have jumped a tooth and that is going to shift timing out of wack. You need to put a fuel pressure guage on the fuel rail and test that. In short, you are past the stage of being able to fix it with a $39.99 on-sale Sears Craftsman wrench set, a Haynes manual, and a bucket of miscellaneous screwdrivers. You are either going to have to go out and buy the tools (and documentation, like the Factory Service Manaul) to troubleshoot it properly or pay someone who has the tools to do it correctly.

Ted

garbage-out.

This kind of reminds me of a weird one I had a few years ago. Intermit no power, pops back thru intake, didn't run worth a shit at part throttle and may even die at times. No codes were present. Finally caught it acting up and it was the crank position sensor. Never came back for that problem after replacing it.

Denny

Hey Ted

That is what i call a answer!.

I have two problems, a car that dont work properly and the fact that i dont know the English technical terms for everything in the car and a lot of other words as well i´m sorry to say. How good is your Swedish????.

You have missunderstood some things i´ve said i think.

1) Backfiring at part throttle, not full throttle. 2) Ignition system completely checked out with a friend's scope and timing is correct and all parts of ignition system have been replaced 3) Car completely within emissions.

In short, this isn't possible.""

1) If i press the throttle as slowly as i can in neutral it will run perfectly up to 3780rpm and then start to miss slightly and the rpm gauge will start to wiggle between 2000 and 7000 rpm´s, if i continue to put more throttle on, it will missfire more and more until it starts to blow back into the aircleaner. It will do the same thing if i would press throttle right to the floor, rev up and BOOM miss miss boom. Sometimes it don´t backfires but just missfires and chokes.

I´ve said nothing about NOT backfiring at full throttle.

2) We tested the ingnition with a timing strobe and it´s behaves correctly. I have replaced the wires and plugs, not the ignition coils.We measured them and they seems ok according to the values that i found on Allpars.com. 3) The cars emissions is ok. I dont know how you are doing the test in your country but here we test at idle and at what they call elevated idle (about 2500-3000rpm) and it passes that test. I have a long sheet of paper with the result of the tests we made but they are at my friends workshop unfortunatley.

We also tested the fuelpressure (OK)and the vacuum (OK)and alot of other things that were OK.

He dont have a scantool for Chrysler, but i will be able to borrow one within a month time i hope.

As i described before i could fool the engine to go just right if i do what i had to do with my old Chevy van with a bad acceleration pump in the carb. I go in about 35-40 mph thrusts the throttle to the floor and starts to pump up and down about one third of the throttles total travelling distance a couple of times and then floor it again and it accelerates just fine.

I think just as you do it must be one of the sensors, probably the TPS sensor that also works as a "acceleration pump" what i understand. I´m not sure about that last thing, but you maybe know that Ted. It seems to me that the engine suddenly dont get enough fuel, but why always at that same rpm regardless of the load on the car, i dont understand that. Could the TPS sensor give me this problem if it´s worn out somewhere in it´s slide range?. TPS=throttle position sensor ..right? The throttle can´t be in the exact same position when i test it in neutral as it will be when i test it on the road for example upphill with a caravan or a trailer, but it will always start to mess around at the same rpm.

As you said...it´s a impossible problem and i hope the scantool will help me otherwise i have to throw my motto away and go to the local Chrysler workshop with the tail between my legs....and i don´t like that, i tell you that!.

And Ted I have access to (almost)a fully equipped workshop with owner and that hasen´t helped me so far unfortunatley, but my hope lays on the scantool. Thank you for your help in this matter, you put some new idéas into my head to try if the scantool takes to long to get hold of.

Janne

Then in that case, the symptoms are consistent with a intermittent secondary misfire. Since only the plug wires and the coil itself are part of this system, and you said you replaced the plug wires, then the next suspect is the coil.

I had thought in one of your prior posts you had said you replaced the coils.

And I am positive in a prior post you said you had replaced the plug wires.

A resistance measurement for a coil is useless.

OK, well then that kind of testing is garbage. Do you drive only at idle speed and only at 2500-3000rpm when you are on the road?

I have a long sheet

Here, 1995 and prior vehicles are tested on a dyno. The car is run from idle up to around 4000rpm in a gradual curve, then back down. They have to have the exact vehicle make/model/engine so I am of the opinion that the curve used is different for each engine. It is probably optimized to try to make the vehicle fail, at least that is how I'd program it if I wrote it.

OK clarification then:, when you "floor it" your going at WOT right?

You see, this basically knocks out the intermittent secondary misfire idea/coil failure diagnosis.

If it was a real ignition misfire such as coil or plug wires, it would do it ALL the time including the time that you are saying that it's "accellerating just fine" regardless of the pumping your doing.

could be. I know what you want me to say, you want me to say it's the TPS so you can go waste more money shotgunning.

It's not an impossible problem - this is why they make scantools. This is your own vehicle, right? Why are you so resistant to buying a scantool?! Here's an example of one that would have worked perfectly for you, check out the price!!!

You really need a factory service manual if your trying to DIY.

Ted