Hi, so I've go this Honda Accord, 1998, V6, 221K miles.

The following items are relatively new but are all up for speculation:
plugs (NGK, just re-gapped them a bit ago, all looked equally burnt)
wires
cap
rotor
EGR valve (cleaned out)
IAC Valve w/ gasket
MAP sensor
fuel injectors (refurbs from ebay)
rear O2 sensor

note: I've done the EGR port clean out and tube extension.
When it was running fine it was getting 23 mpg highway, now it gets 17 max.

Symptoms:
1. takes a few seconds longer to start.
2. seems to bog down during normal driving conditions. Have to push the accelerator down further and further until it finally revs higher and launches the car forward.
3. Using cruise control on the highway, set to 65 mph, accelerates to ~67 mph, bogs down until it coasts down to around ~64 mph, then accelerates again. Basically surging but im not too understanding on the definition of it.


Codes: P0171: System Too Lean (Bank 1) P0170: Fuel Trim Malfunction (Bank 1)

I was able to catch a P0130 randomly (Sensor Circuit Malfunction (Bank I Sensor 1)) but it quickly disappeared.

I initially suspected a vacuum leak but have sprayed all gaskets in and around the intake with carb cleaner, no bogging down, have not done a smoke test.

I pulled and plotted some data. Highway driving. (It may be better viewed if downloaded and opened in excel) The first tab is all the data. The second is driving on cruise control around 63 mph and having the car hold the speed great. Right before this on the graph you can see i was coasting in neutral, just down a big hill for about a mile (trying to save some gas). The third tab is the same cruise control situation but the car is surging trying to keep the set speed.

https://www.dropbox.com/s/su8n5tg6ug...20PM.xlsx?dl=0


At this point I'm thinking it's an electrical issue, either the O2 sensors, the main ignition switch wiring harness, the vtec solenoid, or the ECM itself.. others have suggested the thermostat, vacuum leaks, and the cat being clogged.

If the vtec solenoid was infact stuck, it'd lead to bad timing. When it bogs down at low speeds under load, the sound coming from the tail pipe is very rough, possibly from the timing issue. it sounds thin and like coughing and like it's barely chugging along, then i press the accelerator a bit more and it launches me forward with a nice vrooomm.

The intake boot had a crack in it but i taped it up for now. The engine runs a tiny bit better but I have a strong feeling the issue is electrical based on how erratic it is. Soon after I taped it up the surging would come back. Each time I reset my codes or the ECM totally, the problem goes away for about 5 miles, then slowly comes back more and more until it throws the lean code.


What the heck do y'all think is going on? I'd like to fix this an I am a mechanical engineer, it's just driving me crazy.. If you need more data pulled at a particular time or while I'm doing a certain action let me know!!

EDIT: Added some acceleration data, you can see how the RPMs and speed will drop while the throttle position stays the same, then once i press the accelerator down more, the RPMs and speed quickly pick up. When it's bogging down it makes a slower "chh, chh, chh, chh" sound from the tail pipe.

-Andrew

 

I just joined the forum. sound like your fuel pump is going out or isn't getting good pressure.
Change your fuel filter (if you have one) first.
Your pump could be cutting out when it gets hot but it sounds to me like it doesnt have enough pressure anymore.
A pump can be working but not have the correct pressure anymore due to a worn out pump.

Borrow a friends or buy just the pump for the unit. Or get a used one or aftermarket one. Up to you.