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Mike S.
Mike S., ASE Certified Technician
Category: Dodge
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Experience:  ASE certified
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Dodge Caravan: I need some help. 97 dodge caravan 3.3l backfire

Customer Question

I need some help.
97 dodge caravan 3.3l backfire out throttle body???
- new coil pack
- plugs and wires
- new iac
- new cam position sensor
- I have a new crank position sensor I have yet to put in because the old one is seized in place... Old one is in still.
- tps checked out good
- cleaned throttle body and iac port
- checked harness for melted harness (common issue) didn't see anything.
- fuel pressure stable at 48psi. 50 psi is spec.
- new fuel pump.
- old fuel filter but pressure isn't dropping...
- CAR RUNS GREAT POST 2000 rpm.
Ideas?
Submitted: 1 year ago.
Category: Dodge
Customer: replied 1 year ago.
It also has a rough idle.
Expert:  rpmdiag replied 1 year ago.
Hi, I’m Ron and I can help you.I have been in this business since 1975 and also teach automotive repair. I am confidentwe can resolve your problem together. Please understand that I don't know your skilllevel. I can't see, smell, hear, or touch the vehicle either, so it may take a few replies toget to satisfactory results. Please be patient!I also try to give all of the information you may need, expecting a “positive rating” inreturn. I will also continue assisting you after you have rated me, if necessary. If thereis any reason I cannot get a positive rating, please let me know why “in advance”, so Ican go another direction for you. I am sorry you’re having this problem; I’ll help youthrough it. There would have to be codes associated with this problem that may also help us and it would be my next choice to get some scan data including freeze frame and MODE6. We may even need to use a lab scope on that crank sensor.Thanks, Ron
Customer: replied 1 year ago.
Thats the odd part, there is zero check engine lights
Customer: replied 1 year ago.
https://www.youtube.com/watch?v=Ky1lq53VwA4
Expert:  rpmdiag replied 1 year ago.
That tells me that the computer is NOT working then, it's NOT able to recognize a problem. Disconnect something like the TP sensor and see if the light comes on. The PCM may e your whole issue.Thanks again, and please don't forget to rate me and keep this link in case you need me again later on.Ron
Customer: replied 1 year ago.
The computer is working. I just unplugged the TPS sensor and had 2 codes pop up. po122 and po123 both TPS circut codes. I cleared the codes and they do not come on again. Odley enough the car ran the exact same without the tps sensor plugged i. no change
Expert:  rpmdiag replied 1 year ago.
Okay, but that doesn't mean the PCM will set a code for misfires like you have. Disconnect and injector and see what happens with codes, a different one.Ron
Customer: replied 1 year ago.
Po205 when I unplugged an injector
Customer: replied 1 year ago.
However, when i unplug a spark plug I get wire I get no code.
Customer: replied 1 year ago.
Spark plug wire that is.
Expert:  rpmdiag replied 1 year ago.
Okay, you need to do a compression test, wet and dry including running for dry.Ron
Customer: replied 1 year ago.
Running for dry means what?
Expert:  rpmdiag replied 1 year ago.
No oil added to cylinder and start engine when running compression test, then accelerate to 2000 RPM's then record the difference from idle to 2000. You may have a valve train issue or sticky valves.Ron
Customer: replied 1 year ago.
The front 3 cylinders (ones that are accessible showed 120psi across the board (dry). I was only able to get one test done with the (running for dry) it was 20psi at idle and 25 psi at 2000 rpm. That was with me clearing the gauge pressure every 3 seconds or so to make sure it did in fact return to the same value. The compression gauge is stuck currently in the cylinder so i have to wait for the car to cool off. I should also add that the car smells of horrible exhaust fumes. and the plugs when removed looked wet and rich. see photo
Customer: replied 1 year ago.
Id also like information on testing the crank position sensor. To see if it is functioning properly. When i tried to remove it i could not and did not install the replacement unit i have. Unless you think i should be looking elsewhere
Expert:  rpmdiag replied 1 year ago.
You can check the crank sensor with scan tool or a scope.
Customer: replied 1 year ago.
Ron, what about all the other information I just gave you. And yes I am aware that i can use those tools but what wires? Where do I connect things? Also, I do not have access to an oscilloscope . why did you have me do all those tests? I gave you answers, do you have an opinion on results?
Expert:  rpmdiag replied 1 year ago.
Do you actually have a misfire, or just back firing through the throttle body?
Customer: replied 1 year ago.
I attached a YouTube link above. It has a rough idle and backfires every once in a while. The video explains u backfires every once in a while. The video explains it best. The spark plugs are also saturated by carbon in the attached photo in a prior message there is evidenc The spark plugs are also saturated if you'll look like carbon in the attached photo in a prior message. There is Reminence of some form of smoke also as the engine is warming up coming out the tailpipe and a whitish color which typically signifies a coolant leak four head gasket. It does not smell like cool, it smells like a burnt catalytic converter. I should also note that the O2 sensor's have been replaced less than a year ago by the prior owner
Expert:  rpmdiag replied 1 year ago.
We need to find the reason for the rich running and that also probably plugged the cat too. I would personally get all the scan data I could at this point including MODE 6 and fuel trims and freeze frame.Thanks, Ron
Customer: replied 1 year ago.
Ron, can you walk me through the process? Mode 6? what am i looking for on the short term and long term fuel trims?
Expert:  rpmdiag replied 1 year ago.
Forget MODE 6,it's way too hard to teach over the internet.Trims need to be normal, not too lean or rich.Freeze frame data is important to see where and when the code set.Thanks, ***** ***** don't forget to rate m.Ron
Customer: replied 1 year ago.
please walk me through what normal short and long term fuel trims are? What am I looking for. Please respond as if I know nothing. I'm feeling like your giving me a lot of geric information. You still haven't responded to the prior test that I did ( compression test). Please give me direction.Do... X, y, z (and here's how in detail) and report back. Then when I give you the data. Respond according.The compression test we did tells us that...... So now we can forget about this and look at that.Thanks.
Expert:  Matt C. replied 1 year ago.
Hello, I see the previous expert had opted out of this question. I would like to see if I can help you a little further. I had just watched the video you posted to YouTube, I noticed in the video that the valve cover says 3.9L? You had said this was a 3.3L, Is that correct?
Expert:  Matt C. replied 1 year ago.
Also, do you have access to a scan tool to view engine data? This is going to be very useful to us.
Customer: replied 1 year ago.
Thanks for trying to help me out. Greatly appreciated. I do have access to a scan tool. So far there has been no codes. I do have a scan tool. A photo is attached. It is a 3.3l (vin r I believe) the sticker is just worn off. :)
Expert:  Matt C. replied 1 year ago.
Sorry for the delay, my computer just crashed on me.OK, let the engine warm up to operating temperature then pull up the data for the long term and short term fuel trims and let me know what it says. Backfires through the intake are typically caused by a lean condition so we are going to try and see if the fuel trims are out of spec. The fuel trims will show us if the computer is trying to increase or reduce the amount of fuel to the cylinders. Let me know the readings and we will continue.
Customer: replied 1 year ago.
Thanks, ***** ***** not be by the car until Monday. Hope that's ok. I'll get back as soon as possible.
Expert:  Matt C. replied 1 year ago.
Not a problem, talk to you soon.
Customer: replied 1 year ago.
Here's a video today of the live data. http://youtu.be/QclASiuF4ag
Expert:  Matt C. replied 1 year ago.
OK, other than the backfiring and the rough idle, has there been any other symptoms? Specifically any type of rattle noise and stalling.
Customer: replied 1 year ago.
There has been a small rattle that I can't identify. Sounds weird. Horrible smell from exhaust. Plugs were soaked with fuel. What did the fuel trims tell us?
Customer: replied 1 year ago.
The car does stall every once in awhile. While in drive and idling it has just died twice.
Customer: replied 1 year ago.
Today there was also an PO118 and PO 353 code. (We were unplugging and plugging in the coil the other day when the last tech on the site was trying to get the Ecu to respond. Maybe not the coolant one though. Don't remember disconnecting anything coolant related.
Customer: replied 1 year ago.
And lastly, it seems to stop backfiring once it's warm. Like literally almost non existent. After its warm the idle is very ruff and it hesitates when you accelerate
Expert:  Matt C. replied 1 year ago.
The fuel trims looked pretty decent, slightly lean on on the down rev. I would like to see if you can pull the little inspection cover off from the bellhousing and examine the flywheel for any cracks. Also take a look at it while it is running and check for a wobble.
Customer: replied 1 year ago.
Sure I can do that. I should note that the exhaust creates a white-ish smoke when the engine is cold. Also, while running the exhaust is bad enough to where it will cause anyone that is behind it or near it to get extremely lightheaded and complain.
Customer: replied 1 year ago.
And that is while its running outside, with a breeze.
Expert:  Matt C. replied 1 year ago.
There has also been problems with the harness (behind the engine, firewall side) for the fuel injectors, it would be worth a look at that harness for any melting of wires.
Customer: replied 1 year ago.
Ya, I'm aware of that issue. I though it was only on 2001 and newer models
Customer: replied 1 year ago.
I issue is, I have to remove the intake manifold to get to the harness In the rear.
Expert:  Matt C. replied 1 year ago.
I was just reviewing again what you said you had replaced. You should definitely replace the fuel filter. You may also want to check/clean the EGR and ports.
Customer: replied 1 year ago.
egr is brand new, im pretty sure i know the location of the fuel filter. This is a braun handicap accesable van that was converted from a 97 dodge caravan so the fuel filter looks to be aftermarket and crammed into the least likely part as possible. Hoever if that was clogged wouldnt my fuel pressure drop off during reving? Also i removed the flywheel inspection plate and found nothing abnormal. I can show you a video if youd like. What am i looking for?
Expert:  Matt C. replied 1 year ago.
When looking at the flywheel with the engine running, you would be looking for it to wobble at all. With the engine off you would be looking for any cracking on in the flywheel. I saw you said you were reading 48psi, was that reading taken engine on key off, while idling, or while revving?
Expert:  Matt C. replied 1 year ago.
Sorry, *key on engine off* (been a long day).
Customer: replied 1 year ago.
id have to double check but i now for sure while it was idling it was 48psi. Also when i reved it to 2000rpm it was right aroun 45-48 still i believe. I never tried key on engine off. should i?
Expert:  Matt C. replied 1 year ago.
The only specification I see is with a key on engine off test which states "If the gauge reading equals 338 kPa (49 psi) further testing is not required". That is directly from Chrysler. I would assume that if you are getting that reading at idle you would also get that reading with the engine off.
Customer: replied 1 year ago.
That's why I didn't decide to change the fuel filter
Expert:  Matt C. replied 1 year ago.
OK, well, like I had mentioned, take a look at the flywheel and let me know if you see anything.
Customer: replied 1 year ago.
I did look at the flywheel, nothing looked unordinary. I have a video of it if you would like to see it both still and running
Expert:  Matt C. replied 1 year ago.
It would be hard to see in a video but I wouldn't mind taking a look.
Customer: replied 1 year ago.
http://youtu.be/gqDPXR0vKxc
Expert:  Matt C. replied 1 year ago.
From what I was able to see in the video it doesn't look like there is a wobble to it, but again, I am not entirely sure that would show up on a video. You have a pretty good head scratcher. I am unsure of what else would cause an intermittent problem like this. I am going to opt out of this question so I can open it back up to other experts to see if someone else has any suggestions. Sorry I couldn't be more help
Expert:  Mike S. replied 1 year ago.
There are several things that can cause backfiring back out the intake. The first thing that comes to mind is a blown head gasket. That brings me to my first question, "why did you only check the compression on 3 cylinders". Second, is spark plug wires crossed, next is a too lean fuel mixture like when you have a vacuum leak, weak fuel pump or an injector not working. Next is an intake valve not seating. I might want to also include a clogged exhaust. A shorted spark plug wire. Anything lese that would either cause an ignition spark at the wrong time, that is with the intake valve open or a lean mixture.So, I would complete the compression tests and then I would consider dropping the exhaust pipe and run the engine to see if the backfiring and rough idle goes away. Wait until nitetime and run the engine and look to see if any spark pug wires are shorting out. You will see and hear arcs if any are.
Customer: replied 1 year ago.
I only did compression test on 3 cylinders because the back three are an abolsute pain to get too. However, I can if you think that is a must.Spark plug wires are crossing each other, there's no way around it really. They are not "touching" eachother.I will finish the compression test, and drop the exhaust and report back.
Customer: replied 1 year ago.
Is there a way to see if the crankshaft position sensor is working properly?
Expert:  Mike S. replied 1 year ago.
By crossed spark plug wires, I meant on the wrong cylinders throwing off the firing order.Other than watching the pattern on a scan tool, I would think that if there was something wrong with it, it would set a code.
Customer: replied 1 year ago.
Not to emotion it runs well when it's warmed up. I can't get it to backfire once warmed it.
Expert:  Mike S. replied 1 year ago.
Change the coolant temperature sensor and try it again.

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