Hey all,

I’m having issues with my car breaking up under boost. As soon as it starts to hit 3k rpm it violently breaks up. It had my tuner stumped.

- Hondata COP setup with a P28 S300V3 ECU, LSVTEC, 10:1 pistons, FIC 2200cc injectors, etc etc.

I have done the following troubleshooting:
1. Replaced the distributor
2. Bought a new, second set of OEM Honda coil packs
3. Changed NGK Resistor style plugs twice, and gapped to different sizes
4. Checked and re-sanded grounds + new wires
5. Checked COP wiring and troubleshooted the kit
6. Confirmed tach signal being received on Hondata (for some reason dash is dead).
7. Replaced and confirmed functional Speedfactory 4 bar map sensor
8. Compression reads 145, 145, 135, 145 - BRAND new engine
9. Receiving adequate fuel pressure (50psi) NOTE: Fuel pressure immediately drops during priming and does not hold.
10: AEM FPR diaphragm replaced and is not leaking
11. Timing is confirmed to be good w/ timing light

Not really sure what else to test. Open to any and all ideas!

Thanks ahead of time for anyone’s help. - Isaac

 

It sounds like you having wiring issues to the fuel pump. What size pump is it? I had intermittent issues with mine and had it rewired it completely. I am going to install a relay setup on my pump soon since I have a Walbro 450 that will draw more amps the factory wiring will not handle.

 

Patrick,

I do have a Walbro 450 installed and utilized it last season on a totally different build. I have not upgraded the factory wiring harness to larger gauge wire. Would a weak or faulty fuel pump cause an immediate drop in fuel pressure during priming? To me that sounds like a leaking FPR or stuck injector.

Isaac

 

Do you have a datalog of the car breaking up?

 

I may be able to snag one from my tuner. If not, I can try and log something this weekend. What in particular are you looking for?

 

Mine breaking up came from a bad engine harness which I just finally fixed today! I bypassed the engine harness and wired to dizzy strait to the ECU plug inside the car.....problem fixed

 

I would say what is the a/f is doing while this happens. Usually breaking up is spark related but if the car is falling on its face then its the engine lacking enough fuel. You get no cels when this happens?

 

Hmm. I purchased a Wireworx harness that came pinned completely wrong. I’ve traced all wires to the dizzy multiple times, in addition to checking continuity. Perhaps I hardwire it once in case I missed something. Doubtful, but I suppose possible.

 

a/f should be good. Car made one pull on gate and made 400whp. Broke up badly going into boost and on the top end. It was a one and done pull for fear of blowing the motor. Tuner assured me that if I resolved the break up issue, afr should be adequate to drive and get into boost. It was tuned by HunterTuned on YouTube.

Had a CEL on for something related to map sensor. Realized the original one was fried, because Wireworx harness was incorrectly pinned. New map sensor went on, then got CEL for crank sensor. Found cracked sensor in dizzy, replaced the sensor and cleared CEL. I have since replaced the entire dizzy with a new one. No CEL.

 

I have a woreworx harness in my car, I must have gotten lucky on the pinouts. Its not a company I would recommend. If I could do it it over I would have gotten a rywire piece.

 

I have watched HunterTuned videos, pretty good.

 

Anything out of the ordinary in the log when it starts breaking up.

 

Turn off vtec and see what happens. Could be related to engagement window? 3K rpm is low though

you are WOT at 3k? What happens if you go WOT after 3k?

What fuel type? E85 I assume? Fuel pressure should hold after priming.

Plugs I ran were BKR7E

 

I believe I have BKR8’s. VTEC engagement should be higher than 3k, but I’ll have to verify. Break up occurs WOT or not.. I think. I’ll try and confirm this weekend. Now that you mention it, I never confirmed the ECU pinout for the VTEC solenoid. The Wireworx harness was awful, so perhaps they got the ONE wire wrong

Yes, running E85. These talks of fuel make me wonder if it’s got something to do with the pump. Weird thing was, tuner saw no irregularities in afr. Same fuel setup previously made 520whp on E85, so I would assume 400whp should be no problem.

 

This points me toward a fueling issue. She's running lean under load.
Any problems with breakup in neutral just revving? Fuel delivery. Breakup only when driving? Map sensor/fueling..

 

You got some sharp dudes on here. I think if you can get a log it would help a ton. Good luck on tracking it down, I know these little grimlens can be a pain.

Does your fuel pump have the anti drain back valve? If so, it’s probably failed which is why your fuel pressure falls immediately after priming. And you are correct, it can also happen with a stuck injector or bad regulator, but since you have ruled those out it’s probably just the pump itself. That happening, wouldn’t create your issue though.

Many guys use upgraded fuel pump wiring, and some tuners won’t touch the car unless that mod is done. It’s a possibility that the pump is getting irratic flow, causing a drop in pressure up top and into boost due to not having a good, clean flow of adequate power. But you’d think the tuner would have caught that, because it would probably ramp up your duty cycle on the injectors to compensate. So that as well may not be your issue.

it’s hard to say on this one, I’ve seen some issues like this, but they were either related to cam timing and vtec, or an ignition break down from spark blow out. What’s the smallest gap you tried to run and what PSI is your gate pressure.?

 

please don't say things like this..lol Just waited 5 months and over 1K for harness's for my wife's new build

 

Mine is working fine but I waited 4 months and when I called rywire during that time they had them built and ready to ship same day. I also got my harness and it was shipped with the wrong sub harness. I hope you have no issues.

 

B series straight to obd1 ecu,fuse box in stock location 96-98 ek etc. Nothing super fancy,but also got the tuck in a box to clean up driver side wiring. I have seen some wrong pin outs etc,so hopefully no issues either.

 

Alright! I'm back with some datalogging. I've attached a screenshot of one of the logs, along with the file itself. As soon as the car sees .01+ Map pressure it cuts. You can see the AFR go way lean. I also have a new code, #9 CYL - not sure what it means but it seems like more distributor issues.
There are two logs attached. One attempting full throttle with pretty aggressive cuts, and one with a very gradual throttle and what looks like a small cut. I do see slightly more map pressure on the gradual throttle datalog. I also attached a datalog file with just revving - no load on the engine.

Download the datalog files here: https://drive.google.com/drive/folde...xZ?usp=sharing



Full throttle pull.


Light throttle pull

 

From what I see, it appears your MAP sensor is kaput. Looks like you're getting noooo reading at all from that dude. Homeboy is flatlined like a champ in these pulls.

 

Ahh! Can’t believe I didn’t see that.. must’ve been too focused on fuel... but what!? I’ve re-pinned, confirmed pinout and continuity, plus changed the map sensor. Let me look over the logs. Can someone confirm Map pinout numbers on P28 ECU?

 

 

I’m with TXdragon. Let’s get that MAP working and see if that corrects it.

 

That'll do it...