Pulsing at idle after engine warms up

[CursedH1]

Hey there! Got a bit of a mystery on my hands.

My brand new P400, with brand new IP and PMD < 1 year old has an issue where, after I've driven it a while, usually on the highway - and gotten the engine nice and toasty (on the H1's that means up past 205) - then when I come back to a stoplight and idle, every once in a while I'll get a dramatic, half a second RPM drop that you can really feel. The engine runs like a freight train when driving normally and really hauls the mail - it's only at idle that I have experienced something like this.

My mechanic has confirmed that he's experienced it, but only once so it's not enough for him to figure out what's going on. I'm getting a fuel pressure gauge installed at the IP inlet while its at the shop as well. PMD is relocated and on a giant aluminum heat sink.

FFM and filter media was just replaced about 3000 miles ago. Don't have a clear IP return line (I know I know)....

By itself I'm not worried about it damaging the engine or IP, I'm just worried that its a precursor to a bigger issue. Anyone have any ideas?

Thanks in advance!

 

[Will L.]

Too many variables still. Once you see the pressure and maybe have to set up go pro to record the clear line ya install when you do the pressure gauge, you could see if anything is going on there.

It could be the program hiccup- but also could be an air pocket build up.

Being able to recreate it would be helpful.

And man, be careful with those new rings still being tempered and getting the temps high. Sure fire way to have blowby in short order. Nothing magical about p400 rings...

 

[CursedH1]

Too many variables still. Once you see the pressure and maybe have to set up go pro to record the clear line ya install when you do the pressure gauge, you could see if anything is going on there.

It could be the program hiccup- but also could be an air pocket build up.

Being able to recreate it would be helpful.

And man, be careful with those new rings still being tempered and getting the temps high. Sure fire way to have blowby in short order. Nothing magical about p400 rings...

Thanks Will. I'll be sure to report back once the fuel pressure gauge is in place. I think I put together a parts bag of adapters to get the sender mounted right at the IP inlet. Only one aluminum part - the rest is SS.