Dunc

Update: Post# 18
Update: Post# 23

Background:
The car is an LS/VTEC. It's a 1997 LS block with a 2001 GSR head running on Hondata S300.

Ignition:
- Brand new replacement distributor. It's not OEM, but I had the same problem with an OEM distributor.
- Brand new NGK BKR7E plugs
- MSD 8.5mm wires with 64, 84, 93, 113 ohms resistance (I didn't bother normalizing the reading for a by-foot value because the readings seemed normal enough

Fuel:
- Walboro 255hp
- Brand new fuel filter
- Aeromotive A1000-6 pressure regulator
- RC Engineering 1000cc injectors
- GM 3-bar map sensor

Problem:
2 years ago I was having a bucking issue that I couldn't figure out and I gave up on it and just parked it. This past weekend I decided to try again. I replaced the distributor, fuel filter, did an oil change, drained the old gas, and cleaned up some wiring. I'm still having the same problem as before so I'm stumped now. The car runs fine when it's cold. But after it gets to operating temp it will start having a horrible breaking up issue and the car bucks no matter the amount of throttle applied. When it's bucking I see the air/fuel gauge spiking to 18+. Sometimes the engine will also just die all together. The bucking is sort of gradual. You can start to tell it's about to happen and then as time goes by and I continue driving it gets worse and worse. When this happens I have to stop and wait for it to cool down completely before I can get going again. I'm at a total loss, do you have any suggestions on what to test? Since I replaced the distributor, I'm beginning to suspect it's something in the fuel system and perhaps a faulty fuel pump once it gets warmed up? It's just strange to me that it works while cold, but goes into full derp mode when hot. I'm just so sick of this car now, I just want to fix it so I can sell it.

ZLboosted_EG

I had a similar issue with a cracked plug wire. It would arc on the side of the spark plug wire (part that goes into the head) and not at the tip(where it contacts the spark plug) Would get a nasty jerk/bucking action. Only found out when I went to see if the car had good spark and it arced on my rad support and not on the screwdriver.

Want to say ICM too because of the break up when warmed up. But you said you replaced it with a new unit. Does it still let you drive it or is the bucking so bad it almost pops out of gear?

Dunc

I should maybe rephrase the bucking term to sputtering. It doesn't want to pop out of gear, rather it just has zero power and you can't go anywhere. The sputtering is bad enough that it's impossible to drive the car and creates a jerking sensation. If I come to a stop there is no way I can accelerate again.

When you had your plug wire issue, did it occur only after the engine was hot and were you able to visibly see the crack?

ZLboosted_EG

Oh ok. So feels like a weak spark, engine losing power? So it's a beast when cold, and gradually dies off as it warms up?
Did you replace the dizzy recently or 2 years ago when you first had the issue? Have you tested the new ICM? I've seen defective aftermarket BNIB icm a few times. Only had good success with OEM coil and ICM

Occurred after it was fully warmed. Would sputter (on 3 cylinders) bad off the line, but as I gradually gave it gas (with the sputtering still happening) above 3500 it would run on all 4. No visible cracks.

Dunc

I wouldn't say it's a beast, rather it's driveable. It's smooth and has the ability to accelerate like a normal car. But once it's warm it's just awful and can't do anything. I couldn't even drive it off a cliff if I wanted to.

I rebuilt the internals on the OEM dizzy 2 years ago with OEM parts. Since that didn't fix it I decided to try a whole new one. So this past weekend I bought a new aftermarket dizzy and swapped the entire thing. No change.

This isn't mimicking your issue as close I think. My problem isn't RPM dependent and happens at all rpms and throttle levels.

ZLboosted_EG

Yea unfortunately it's sounding like it. Does the s300 show anything out of the ordinary? Hope you figure it out

Dunc

Hmmm I may have a lead to try now. At lunch I tested the TPS sensor. I was getting .623v closed and 4.99v open. From some research it appears it needs to be .5-4.5v.

So here are my thoughts. I think the culprit may be the TPS sensor. At a minimum, the sensor is out of spec. But to explain why it happens when the car is hot, I think the circuit inside the sensor has contacts that are effected by heat and perhaps separating or something or just going haywire. For $31 I'm going to buy a new one after work and see if that corrects the issue. I also need a new brake caliper so it'll be a few days before I can provide results.

ZLboosted_EG

Nice, and a tps out of calibration would do that. But the thing that bugged me was the only when warm part. You could be right because I know main relay contacts stick sometimes when hot. Like you said it's not too expensive.

Does your throttle body have the OE rivets or bolted in? Maybe they loosened up a tad, who knows

Blackdc298

Did the new Tps fix the sputtering issue?

Dunc

No it did not. After I switched the TPS I went for a drive. I didn't even make it a mile down the road and could barely make it home. It has sat since then.

I'm back at it again now to try a couple more things before I send the car off to the guy who tuned it for me to work on it instead of me. I just want the damn thing functioning so I can put it on the market to sell. I don't need the money for it, but I'm buying a new truck in about 2 months and want the thing out of my hair.

Next up I'm going to replace the fuel pressure regulator and the pump. After that I'll be at a loss because I'll have replaced the ignition system and the fuel system. I'll only be left with injectors, the OEM injector controller box thing, and the ECU. I'm not confident at all that the regulator or pump will fix this.

tamboo

sounds like when my intake cam jumped a notch after the coil took its final dump.

Dunc

Wouldn't it make it buck all the time if the cam was off by a tooth?

wunfstgsr

Maybe its your ECT sending unit or maybe the ECT sensor both under the dizzy! The ECT sending unit sends the engine temp to the ecu.. maybe its bad..

Dunc

Hmmmmmm I'll have to check that out. Can air bubbles in the cooling system damage the ECT sensor (more than 1 occurence?)

crazyhouse2011

lol.... 5 months later he responds.

good luck on fixing your issue, OP. i hope its the ECT. Then you can finally unload that car.

egsleepercivic

I am actual curious if the TPS was calibrated after being replaced, the original sounds like it just needed to be adjusted

IF OP checks back - DId the new tps read .5 closed and 4.5 WOT ?

tamboo

it actually ran pretty good til it was warmed up, the tps was bad during the same period so it was complicated. i still get hesitation once in a blue moon when accelerating from a stop, it's very puzzling.

Dunc

Yes I calibrated the new TPS. I do not think it's the ECT sensor now. I did a datalog before just replacing the sensor and the datalog shows the ECT reading a steady value. The datalog was of me just cruising. Below is the youtube video showing the sensors and also the timeframes when the bucking occurs. Take a look at the MAP sensor reading during that time. I don't think it is the MAP sensor because I vaguely remember replacing that a long time ago when this problem first started which resulted in no change. I'm beginning to suspect that the fuel pump is the culprit. I think that maybe the fuel pump starts failing when it warms up after a little bit of operation. Perhaps it's the fuel regulator or the injectors. Any thoughts?

Bucking Occurs at:
0:05-0:10
0:22-0:26
0:29-0:35
0:45-0:50
1:15-1:21

wunfstgsr

i would look into stuck or cloged injectors! but i think your on the right track. Any data loging on the IAT sensor?

Dunc

I'm taking the injectors out today and shipping them back to Precision to get flow tested. If they come back normal I may just purchase a fuel pump....not really sure how you can test a pump while driving.

The IAT is in that datalog video. It was around 122*

tamboo

could easily be the fuel pump, you'll need one sooner or later so may as well have one handy.

Dunc

Just got a call from Precision on the injectors. They said they were all functioning normally. (3) were flowing at 87% and (1) was flowing at 80%. They recommended that I replace that one which I did. Now I'm just waiting for them to be shipped back to me.

I had a feeling they weren't the culprit, but at least they are ruled out now. I guess I'll be buying a new fuel pump to see if that fixes this problem.

Dunc

I finally found the problem this past fall...I'm pretty sure. I ended up replacing the fuel pump, testing the injectors, the entire ignition except for plug wires, fuel filter, TPS, and MAP. It turns out it was the injector wiring. I only looked because one of the times it was bucking I was able to see a DTC code and found it to be related to injectors.

The place that originally installed my larger injectors did a T-solder joint and left the OEM injector connectors in the mix. They wrapped the joints with electrical tape. Over time with normal catch can oily fumes, the electrical tape was rendered useless. I had injector wires touching metal pieces/hoses under the intake manifold and creating electrical shorts. On top of that the injector resistor box wiring needed to be redone.

I rewired the resistor box and cut the OEM injector plugs off completely so I could solder in the connectors I'm using now and have a good connection with heat shrink. After doing that the car has been running with no signs of bucking at all. I've only driving it about 50 miles or so but I'm feeling confident that was the problem.

Only issue now is that I get a vtec spool code as soon as I get to the vtec engagement point. I'm going to check the wiring first this time and then go into looking at mechanical pieces.

It was fun feeling boost until 4400rpm when vtec tried engaging and the car just stopped all acceleration. Sucked because 4400+ is where it really starts to accelerate. I had some older nissan next to me wanting to race and I just had to keep my head straight ahead. I was thinking to myself, "this is the one time you get someone wanting to play and your excuse is the, typical untrue, 'oh my car isn't running right blah blah blah'" lol. He did a 'flyby' and judging by it I would have rekt him. So disappointing!