Volvo 855T popping during deceleration

henrysin44 · Post by **henrysin44** » 24 Jun 2018, 16:13

A few days ago this phenomenon started, usually when I let off the gas the RPM will hold for a second then start engine breaking but now when I let off the gas it makes this rapid popping sound for a second or two then starts engine breaking. Happens in every gear, I did replace the spark plugs with NGK nickel plugs (0.028 gaped) a few days ago, but honestly can't remember if the popping happened before or after.

The ECU is tuned for M56 manual and green injectors. Also its unfortunately straight piped, there is a flex pipe that could be making the popping but the sound correlates to feel as in coasting isn't smooth when off the gas.

Post by **tryingbe** » 24 Jun 2018, 17:57

No catalytic converter/muffler?

henrysin44 · Post by **henrysin44** » 24 Jun 2018, 18:10

tryingbe wrote: ↑24 Jun 2018, 17:57 No catalytic converter/muffler?

Theres a cheap cherry bomb muffler but no cat, I do have a R exaust system with a 19T that I plan to put on my motor soon, just waiting on a turbo rebuild kit to come in.

I just took the volvo for a quick drive on a hilly backroad and paid close attention to its behavor. If in third going 25 or fourth going 35-40 it will have rapid popping and slight bucking if I let off the gas then after a few seconds it will start engine breaking (which is normal minus the bucking and popping).

Post by **bmdubya1198** » 24 Jun 2018, 21:22

Has it always done this with your current exhaust setup? If so, I'd blame it on the exhaust. My cousin had a cherry bomb on his S70 T5 and if he ran it in low gear while doing 25-30 through the neighborhood, it would pop when he let off.

henrysin44 · Post by **henrysin44** » 24 Jun 2018, 22:02

bmdubya1198 wrote: ↑24 Jun 2018, 21:22 Has it always done this with your current exhaust setup? If so, I'd blame it on the exhaust. My cousin had a cherry bomb on his S70 T5 and if he ran it in low gear while doing 25-30 through the neighborhood, it would pop when he let off.

Always yes but a month ago i tuned my ECU with a T-5 manual transmission BIN and it stopped popping until recently. I don't mind the popping its the slight bucking with it thats annoying. Im wondering if it might be spark plug related, i previously had those fancy 4 ground straped iridium plugs and recently swapped them for a regular plug

Post by **tryingbe** » 24 Jun 2018, 23:07

I think the holes in your cherry bomb muffler are all plugged up. Factory muffler uses a baffle design.

henrysin44 · Post by **henrysin44** » 25 Jun 2018, 00:07

tryingbe wrote: ↑24 Jun 2018, 23:07 I think the holes in your cherry bomb muffler are all plugged up. Factory muffler uses a baffle design.

Plugged up? As in by design or clogged? Its the cherry bomb turbo btw.

henrysin44 · Post by **henrysin44** » 25 Jun 2018, 14:33

Mystery solved! It was the MAF sensor!

I ran into a volvo tech I know in my hometown, hes been away for awhile and wanted to check out my car after all the mods and work I've done to it and he noticed I've been using a K&N filter and told me never to use them as the filter oil gets stuck on the MAF sensor. Went to AutoZone got a paper filter, cleaned the MAF, and now the popping and bucking us gone!

Never putting K&N anything in my car, oil filter would make my valves tick and the air filter clogs up my MAF, guess sometimes cheap parts are better.

Post by **bmdubya1198** » 25 Jun 2018, 14:41

I've never been a fan of K&N. My GLT came with one when I bought it, but I replaced it with a Mann OEM paper filter.
I grabbed a K&N for my R from the junkyard because I've heard they do help along with other mods, and it was $4... great deal!

Glad you got it fixed quickly!

henrysin44 · Post by **henrysin44** » 25 Jun 2018, 17:03

bmdubya1198 wrote: ↑25 Jun 2018, 14:41 I've never been a fan of K&N. My GLT came with one when I bought it, but I replaced it with a Mann OEM paper filter.
I grabbed a K&N for my R from the junkyard because I've heard they do help along with other mods, and it was $4... great deal!

Glad you got it fixed quickly!

Welp I spoke too soon, popping and bucking is back, unplugged the MAF while it was running and there was no change to the idle, to the best of my knowledge that means a bad MAF. I have a few laying around to see if it makes a difference. Although sense I bought the car back in '16 its had a code set for bad O2 sensor maybe its finally too toast.