94 Honda Accord EX Engine Surging — Stumped

[quote=”ben_tech” post=157045]Here’s what I did today on this:

– Replaced the compromised old Nichicon 33uf capacitors on the ECU circuit board with new Nichicons of same value. No immediate change in symptoms.

– Tested with transmission in Neutral, no change in symptoms. Presumably since it’s still acting up in Neutral and I haven’t seen any flashing from D4 (although I haven’t jumped the transmission service connector) it’s not the transmission.

– Back probed the engine coolant temperature sensor connector. There was no way I could get multimeter probes in there by hand with sufficient accuracy to maintain contact with the pins inside the sensor. Instead, I used needles to backprobe the connector and attached alligator clips to those. The measurements were taken with the electrical connector still plugged into the sensor. The reading was 800 ohms or so with the engine off and stone cold. I then ran the engine hard to reach max operating temp (fans on several times). Turned engine off. 140 ohms. Increased smoothly up to 200 ohms or so within a few minutes as the engine cooled just a bit (still hot).

– Unplugged several vacuum lines from the throttle body one at a time, plugging the holes on the throttle body to see if the engine smoothed out. No changes.

– Did the full idle speed adjustment routine again:
1) Unplug service connector and apply jumper
2) Unplug IACV electrical connector
3) Turn car on
4) Wait about 30 minutes for engine to heat up fully, fans on a few times
5) Set idle screw so that RPM tach hits just below the second notch on the gauge, about 700 rpm
6) Turn engine off
7) Pull two fuses (backup and ECM) for a couple minutes to reset ECU
8) plug in service connector
9) Plug in IACV
10) Turn on car and let idle for 20 minutes with everything off and not touching throttle for ECU to relearn

The symptoms are always better when the engine is thoroughly heated up but very bouncy between 1.25K and 1.5K RPM.

There’s the fuel pressure, pump, filter to look at I suppose. Also I did notice some liquid maybe water (no odor) on the ground under the tailpipe and around the engine valve cover gasket, may be just condensation. Could try water remover in fuel just in case.

There’s also that 220uf cap in the ECU that looked like it had leaked a little bit, didn’t have a replacement for that. leaking a little only causes a cap to be slightly off value though not sure that would cause the problem. Could get a replacement used ECU off of ebay perhaps for testing.

Sucking on MAP sensor may have been inadequate test, could get vacuum pump to test it more thoroughly.[/quote]

Nice to see a proper IACV adjustment, however, as I have said before the ECU if it has any failed components, might have other ones that you can’t visibly see. Diodes for example. I would recommend going to a junk yard a pulling one out. Also if you could get a video of your symptoms that would be nice as well. The reason you can go to a junkyard is if the ECM has the same problem you can return it and get a different ECM from a different car. It shouldn’t be that expensive, also no shipping fees.

[quote=”ben_tech” post=157127]Today I decided to test the Engine Coolant Temperature (ECT) sensor more thoroughly.

I drained the coolant (will re-use it later).

Then I took the ECT off (tricky to reach but loosening up the wiring harness in front of it made it possible to get a deep socket on the ECT then jam a ratchet in there.

Once I had it out, I first put the ECT sensor under a cold tap –

Cold tap: 3700 ohms (maybe a little low but I didn’t have ice)

I then let it warm up to room temp, the reading ranged smoothly up to:

Room temp 21 degrees C : 2000 ohms (good)

I then heated some water –

Hot stove water at exactly 100 degrees C : 154 ohms

154 ohms is out of tolerance. This part is supposed to be between 200 and 400 ohms, about 300 ohms at 100 degrees C.

Whether that would be the problem here I can’t yet say after so many dead-end leads on this project.

I ordered Honda part number 37870-PK2-015 since the knockoffs had such bad reviews. Will report back if this fixed the issues on Thursday.[/quote]

I really feel like its an ECM, if the coolant temp sensor doesn’t resolve the issue, junkyard it up for an ECM and plug and play.

[quote=”ben_tech” post=157278]Today I replaced the ECT sensor with brand new OEM part, no change. As a part of that job I did drain/fill/bleed the coolant system and squeezed the hoses and got the engine heated up with a no-spill funnel set attached to the radiator with the front end jacked up 2 feet for optimal air removal from the system.

I redid the idle setting procedure and this time set the screw as far in as it would go which looks like maybe 650 rpm if I had to make a guess by looking at the tach. No difference (been here before).

Tested the MAP sensor properly today with a vacuum pump.

Results:

2.9v on the third pin (backprobed) to battery negative.
5 inHg: 2.41v
10 inHg: 1.93v
15 inHg: 1.47v
20 inHg: 1v
25 inHg: .6v

Pressure released: 2.9v

No leaks, pressure held as long as I wanted.

I think we can call the MAP sensor good now.

Got to be the ECU…. or maybe a fuel pressure issue but less likely that due to constant CEL code 14…. at least the ECU is part of Honda’s troubleshooting procedure for CEL 14.

Thanks for trying to help me, I do appreciate it. Any other ideas are welcome. I’ll be trying to get my hands on a decent used ECU for this car now.[/quote]

Have no doubt, if you checked the ECT and it was out of spec, it will still help to have a new, correctly outputting ECT.
The ECM shouldn’t be hard to find, shipping shouldn’t be too bad either, here is the Honda part number for the ECM: 37820-P0B-A51

Good luck and keep us posted!

[quote=”ben_tech” post=157281][quote=”DaCoder” post=157280]The ECM shouldn’t be hard to find, shipping shouldn’t be too bad either, here is the Honda part number for the ECM: 37820-P0B-A01

Good luck and keep us posted![/quote]

The part number of the original ECM in this car is 37820-P0A-A51. What the differences if any are I have no idea but I’ll buy the same part number as I have here.

Thanks, I will keep you posted.[/quote]

Ah, refresh this page, I figured out that the model number i gave was M/T only, there are two ECM numbers for A/T, this is from estore.honda btw.

Looking up prices, ebay is 109 and up, the 50 dollar one is water-soaked. At my local junkyard its and i quote from the prices list:
“Item: Control Module Price: $19.99 core deposit: $3.99”
So if I went out and got one, confirmed that it works, and I could ship it out to you, for a cheaper price than Ebay.

[quote=”ben_tech” post=157283][quote=”DaCoder” post=157282]Ah, refresh this page, I figured out that the model number i gave was M/T only, there are two ECM numbers for A/T, this is from estore.honda btw.[/quote]

Gotcha. I wonder if the aftermarket alarm system the dealer installed will be a problem with swapping the ECU.[/quote]

Aftermarket alarm systems are always a problem in my experience. That said, Honda ECU’s very rarely have an issue. I’d make absolutely sure you eliminate all other possibilities before going there.

Good luck.

The flow chart pretty much makes you eliminate every other possibility. The FSM procedure also calls for a break out box that you attach to the computer to take your readings from. I doubt the poster has access to one. It would be nice to rule out a wiring problem or other issue before replacing the PCM. If replacing that doesn’t fix the problem, then you’re back to square 1.

In addition, the aftermarket security system is suspect. I’ve seen many issues with them and especially their installation. If the harness was cheesed up during the installation, that could be the problem.

This is one of those situations where there is really very little I can offer via the forum. On an older car like that, with aftermarket parts, it’s almost impossible to help without seeing it in person. If the idle or performance articles didn’t help, there’s not much more I can offer.