Stumble, hesitation and back fire under load

[Danny915]

Ive searched the forum for the past week trying to see if this is a common thing but i need to take a more direct approach. Motor is a 2.5 m20 with a dinan chip. Cat delete and aftermarket muffler. I have done the following in attempts to fix this problem:
-O2 sensor
-CPS sensor (dealer part)
-cleaned MAF
-plugs
-wire
-coil
-cap and rotor
-valves adjusted
- smoke and leak down test

Issue: 1) Car drives fine daily, no problems at all, I drift the car as well and flat out second gear for 3/4 of the day no problems. Now after a while a stumble starts around mid rpm range while accelerating once past this point it drives ok again but i notice i slight decrease in power.
2) very randomly while driving under a load, could be accelerating in 3rd to climb a slight hill or 5th gear going WOT, car stalls for a split second (no power) and then runs again, check engine blips, and then huge backfire and a flame out exhaust.

Im going to clean out tps today in hopes of fixing something but if anyone has any ideas plese let me know. Thanks in advance.
-Dan

[Swanny]

My brothers car is doing something very similar and have yet to figure out the cause....been looking for answers but haven't found much. Only thing I haven't gotten into yet is the cap/rotor/wires/plugs which were all inspected but perhaps could have failed since installation. He's probably going to break down and take it to a shop to get a full run through soon.

[Scallywagon]

Maybe FPR needs to be checked, what size injectors are you running and, what does Dinan tune for?

Sounds like its really rich obviously, what did the plugs you pulled tell you?

Maybe a stomp test to see if the AFM is actually bad.

[Danny915]

Maybe FPR needs to be checked, what size injectors are you running and, what does Dinan tune for?

Sounds like its really rich obviously, what did the plugs you pulled tell you?

Maybe a stomp test to see if the AFM is actually bad.

Stomp test was done not too long ago, will try again today to check. Injectors are stock and I have no clue about the chip, installed by PO, all i know is i redline higher than stock cars.

[Danny915]

My brothers car is doing something very similar and have yet to figure out the cause....been looking for answers but haven't found much. Only thing I haven't gotten into yet is the cap/rotor/wires/plugs which were all inspected but perhaps could have failed since installation. He's probably going to break down and take it to a shop to get a full run through soon.

Is it consistent with his car or random as well?

[Swanny]

Usually will only pop up during WOT. Doesn't matter what gear or what speed. Since his tach is dead I couldn't associate it with any specific rpm range.
I had slapped a fuel pressure gauge on and drove around with no change in pressure, was doing some electrical testing on his sensors and was worried about the air temp sensor on the AFM being bad and throwing off the ECU but hadn't any extra parts to test it out.

[Danny915]

Usually will only pop up during WOT. Doesn't matter what gear or what speed. Since his tach is dead I couldn't associate it with any specific rpm range.
I had slapped a fuel pressure gauge on and drove around with no change in pressure, was doing some electrical testing on his sensors and was worried about the air temp sensor on the AFM being bad and throwing off the ECU but hadn't any extra parts to test it out.

did you ohm out the cps?

[jlevie]

My first suspicion would be a flaky CPS. Try a new OE part.

[Danny915]

My first suspicion would be a flaky CPS. Try a new OE part.

going to test it again to see if its out of spec before ordering a new one, whats the spec again?

[Swanny]

Sure did. Believe the magic number is ~550

[Danny915]

bump for more opinions

[603Racing]

Battery connections tight and corrosion free? Sounds like it's a sensor or electrical issue. Try swapping around relays and check relay wiring. Check grounds.

[Danny915]

Think i may found the issue, the pins in the fuse box connector (c101 i believe its called) were dirty, cleaned them up, tps tested good. So now i just need to driv it a bit and see. Im at the track again this weekend so that will be optimal testing grounds. I will keep you guys updated, thanks for the help.
-on a side note, one of the wires on that connector seemed to have shorted at some point, jackets was melted completely off. Wire number on the connector is 20. On the engine side it is a red and yellow wire, on the fuse box side it is (was lol) a brown wire. According to the internet early models had a brown wire for an earth wire and late models had the red and yellow wire for abs module. Maybe an early model fuse box was swapped in, i really dont know.

[603Racing]

Glad you think you found it. Both of those c connectors can have corrosion issues... the 191 and 101.

[Swanny]

Did that work out for you?