Wow - this is a little weird.

So after a 100 mile run I came off the interstate to a intersection.

The van performed well on the interstate - no issues at all.

Then when I pressed the gas from the stop at the intersection, the van started to backfire horribly. It almost didn't move. I had to pump the pedal to get it to move. As soon as it go to about 2000 RPM (which took about 30 seconds - way longer than usual) the backfiring went away.

So I pulled over, left the van on and for the second time plugged in my BASX OBD Bluetooth adapter. I watched the sensor readings while it backfired. I found that the intake air temp went from 150 to 220 instantly. When it did that the timing was retarded from 15 to 0. It wasn't till the IAT sensor went back to 150 - that is when the timing advanced and the backfiring went away.

I just now ordered a new IAT sensor. I have had this happen once before after the same conditions and just wrote it off as a really hot engine and/or carbon that dislodged in the combustion chamber.

I was thinking of anything else that could cause this...maybe the belly pan gasket is going??? I will check that when I do this job, but I have been getting consistent gas mileage and not losing any oil, so I doubt it. Also I drove 100 miles on my trip out and this was my 100 mile return trip...so you would think it would have done it at some other time during the day.

If you think you have any ideas - please let me know. I think the sensor is just toast. On rockauto.com this sensor has a heart by it - meaning it is one of the best selling parts for the van

Thanks all.

 

Just a thought -

I am surprised that the CEL didn't go off after a event like that...

But, our PCMs I guess are not that sophisticated

 

After doing some research.

My IAT sensor is probably experiencing heat soak. I noticed after stopping for a few minutes, at restart the engine was at 220+ degrees and quickly went back to 200 after about 1 minute.

I will still replace it, but now I am thinking or relocating it to the air filer case-maybe. What happens when our vans see a IAT of 170+ timing goes to 0 and it gets as lean as it can be - that would cause detonation right?

I do experience high temperatures being here in Florida during the summer. I did have a similar situation again when I went to Jacksonville, albeit it wasn't as bad. I did notice that using 93 octane seemed to help the issue coming home.

 

So it gets a little more interesting. It seems like every time I do something on this van there is a mystery


I purchased a new IAT sensor from RockAuto. It is the Airtex version. Now, after looking at ebay and other sites, it looks like RockAuto did send me the right sku (all the pix on different sites showed the same sensor), but it isn't the right sensor.


Here is the sensor connector they sent me...





Here is the stock one...







As you can see the connector is different. I couldn't get it to work.


I had to put the OEM one back in.


I tried using the new sensor and it gave me a IAT code, which means it wasn't working. What was really interesting about driving around in default PCM mode was the van was a lot more responsive and putting more power to the ground. Maybe this sensor has been bad for awhile?


Well, now I need to find the real one. Ill probably just end up going to the dealer and get a OEM one. Just additionally, the old one did have burn marks and seemed brittle, and that makes sense after being in the hot environment for 13 years.


It is always something, isn't it

 

Just an update...

I replaced it today after getting the right one from NAPA.

It seems to run smoother, especially at idle.

The listing on Rockauto for the Airtex is incorrect and they are fixing that now.

Van on guys...

 

Update:

I went on the same 250 mile round trip and exposed the van to the same exact conditions.
I had no issues. The IAT sensor readings were consistent, even when the van was put into the same fast run and then stop situation. Also, there was no spiking of the reading or, from what I can see now, erroneous readings.
I experienced no detonation and had spark advance from idle to 5000RPM, in all situations.

I am now running 89 octane just for insurance until summer is over. Better safe than sorry.

I did notice an improvement of 1+ MPG and I had 300 pounds of more weight* as compared to the last time I had the problem.

*(father in law and fishing equipment - wife caught the most fish - a few snapper and a mackerel LOL)