92 Civic VX stumbling/hesitation

[falconfxr]

I'm brand new to this forum, though I've poured over this entire thread. I am seriously blown away by the depth and resourcefulness of the users in this thread! I'm a new 92 VX owner and am running into similar challenges as Bruce. When I bought the car, the check engine light was on (indicated O2 sensor). I have tinkered with EG civics for years, but never a VX. I had no idea what I was getting into! After tons of reading, I'm hooked on this little car and its potential. I'm not used to VTEC and all the sensors though. So I ordered the OEM sensor. While waiting on that, I gave it a basic tune up (cap, rotor, plugs, wires, oil change, fuel injector cleaner).

As a VERY important note: The car did NOT hesitate or surge/buck with the bad sensor.

I got the sonsor, swapped it out and now when gently-moderately accelerating it has a really bad hesitation and bucks like it's missing or something. It is really hard to keep a steady speed just because when I back off of the throttle to cruise, it starts feeling like it's missing and losing a little bit of power. Falling back on past civic issues, I replaced the ignitor module and coil. No change. I don't get any codes or lights, but I know this little car is supposed to run better than this!

My limited tinkering makes me lean towards ignition/electrical or fuel issue, but again I've never messed with the sensor controls like this little car has.

Other issues, which I don't know if they are related or not, are:
1. fuel economy has yet to break 36 MPG.
2. Gauge cluster backlight and HVAC control backlight do not work. All buttons, warning lights, signals, etc work. But no backlight. (Makes my night time commute a little interesting...)

Any ideas? Thanks in advance!!

[falconfxr]

Taking in what I read in the previous posts, on my way home tonight I noticed that the car ran great until the temp came up. I remember reading in one of the posts that until the temp reaches a certain point that the engine uses presets instead of real time adjustments based on sensor feedback. Which sensors are delayed for temp? What systems (fuel/air/ignition...) do they control?

I really hope this is a solvable issue! I love this car until it starts hiccuping!

[add|ct]

Well as for the back-light, I'm not sure about the HVAC lights but IIRC the lights for the gauge cluster run through the brightness control switch to the left of the steering wheel.

Mine currently needs replacement, the switch itself. However, according to the Factory Service Manual it seems I can just jumper the correct 2 wires it will run at full brightness. So, my advice is to get a FSM and see the electrical section regarding that circuit. If that's not it, perhaps it's a wiring issue. Have you checked all fuses on the vehicle yet? Tedious, I know but might be worth it for just 1 blown, right?

However, I don't know off hand what the vehicle relies upon for closed loop live control. I'd imagine the fuel injectors, perhaps the IACV(unless its only temperature dependent since it has coolant pass), etc.

02 and ECTS report to the computer, they aren't computer controlled.

So, you had no bad symptoms on the previous 02 sensor? Is that all that changed since the bucking developed? Have you changed the fuel filter on the firewall?

This car MUST have OE NGK 4043 plugs (ZFR4F-11) by the way and it's also VERY picky on plug wires if you didn't get that clearly before.

MAP sensor test the leads into the harness?

Have you cleaned the EGR valve AND the parts on the IM? Could be carbon knocking/pinging once hot?

You used a fuel system cleaner like what? Some are solvent based and others are detergent based.

PS: I have a potential head gasket failure in my app currently and also just recently replaced the engine mounts. The rear main and the sub-frame mount by the A/C compressor bracket were each broken.

I suppose you could always check the timing belt condition, valve clearance, mechanical or distributor timing, etc.

Ignition sounds like you're fine there. Maybe check the engine grounds for kicks. Have you tried doing a voltage drop test to see if voltage between the battery and alternator aren't running into resistance? You could always get fuel pressure readings since you will be taking the service bolt off of the fuel filter if you can rent/have a gauge for fuel pressure testing. The pressure is supposed increase with the vacuum hose at the FPR removed from the IM while running, as a reminder for the quick test there.

In the back of my mind, I just wonder if a computer or fuel content-type issue is going on for my app. However, the OP replaced his computer to no avail...so. Not enough evidence to point there. Stress testing the ignition system under load would be great. I just don't know how to do that particularly, to be honest. That would at least eliminate ignition source in theory(assuming igniter/coil/rotor/cap/wires/plugs are all fine etc).

PPS: I've also had poor startup idling issues lately BUT it's directly related to when my coolant consumption gets to the point that air is at the ECTS and IACV affecting the idle really badly. Also, the car wants to stall when the cooling fan first kicks on but it's always done that.

[mrmad]

Originally Posted by falconfxr

Taking in what I read in the previous posts, on my way home tonight I noticed that the car ran great until the temp came up. I remember reading in one of the posts that until the temp reaches a certain point that the engine uses presets instead of real time adjustments based on sensor feedback. Which sensors are delayed for temp? What systems (fuel/air/ignition...) do they control?

I really hope this is a solvable issue! I love this car until it starts hiccuping!

I think you want to determine if the car is misfiring in open or closed loop. The car will be in open loop when warming up or at higher throttle settings. If it runs well warming up and at higher throttle settings, I think you can eliminate ignition/fuel delivery/TPS/MAP sensor.

The other system that functions at different operating temps is the EGR. The EGR valve does not open when the operating temp is cold.

I have a CRX and an Integra GSR. I rebuilt the engine in the Integra last year and replaced the O2 sensor. The car ran great warming up, but once at operating temp, it would buck like crazy when trying to lightly accelerate. If I pushed the throttle more it would clear itself out and run well. Since the O2 sensor was new, I started troubleshooting the TPS, etc, and spent a few weeks in frustration. I finally replaced the new O2 sensor and it ran great. The car never gave a CEL indicating the new O2 sensor was bad. It was a painful lesson in making assumptions that a new part was a good one.

[falconfxr]

Addlict,

Thanks for the input! Going down some of it, I had heard about the engine's pickiness prior to the tune up, so I was careful to only use OEM spec plugs, wires, etc. The fuel cleaner was an STP product (likely titled "fuel injector cleaner"). The timing belt and water pump were just done, tho not by me. I don't lean toward distributor timing just based on the idle RPMs being perfect. I went back through the FSM yesterday to double check that. On your suggestion, I checked the ground connections, and did clean one in particular. No change tho. I've never messed with vacuum pressure, so I'll either have to experiment (not my forte) or wait til my mechanic takes a look. What I have never messed with before is the EGR. No other EG civic model has one, do I've never played with that at all. My hesitation in general with paying anyone, even the old Honda guy I use, is that VXs are so rare that finding someone familiar with the D15Z is really tough. Just a quick glance through the FSM reveals how different the power train is.

Mrmad: thats exactly what I'm trying to figure out! It's most definitely a closed loop problem. The first few minutes while the car warms up, she is very smooth throughout the power band. As soon as it hits normal operating temp, the hesitation and bucking start. Unfortunately you're the second one to suggest a bad replacement O2 sensor. Is there any way to test that without buying another one to compare?

[mrmad]

Originally Posted by falconfxr

Addlict,

Thanks for the input! Going down some of it, I had heard about the engine's pickiness prior to the tune up, so I was careful to only use OEM spec plugs, wires, etc. The fuel cleaner was an STP product (likely titled "fuel injector cleaner"). The timing belt and water pump were just done, tho not by me. I don't lean toward distributor timing just based on the idle RPMs being perfect. I went back through the FSM yesterday to double check that. On your suggestion, I checked the ground connections, and did clean one in particular. No change tho. I've never messed with vacuum pressure, so I'll either have to experiment (not my forte) or wait til my mechanic takes a look. What I have never messed with before is the EGR. No other EG civic model has one, do I've never played with that at all. My hesitation in general with paying anyone, even the old Honda guy I use, is that VXs are so rare that finding someone familiar with the D15Z is really tough. Just a quick glance through the FSM reveals how different the power train is.

Mrmad: thats exactly what I'm trying to figure out! It's most definitely a closed loop problem. The first few minutes while the car warms up, she is very smooth throughout the power band. As soon as it hits normal operating temp, the hesitation and bucking start. Unfortunately you're the second one to suggest a bad replacement O2 sensor. Is there any way to test that without buying another one to compare?

The new O2 sensor that was bad in my Integra measured an open circuit with a DMM. Not sure of the pinout of a 5 wire VX O2 sensor, but I'm sure it can be measured with a DMM. Maybe the service manual in the link below would show you the pinout or some of the VX owners here could tell you.

[add|ct]

http://www.youtube.com/watch?v=stFhLSHsOGg

^For O2 testing.

I know in the FSM that there is information on testing the 02 sensor itself. My LAF was dead and throwing a CEL when I got my VX. Replaced it and no more code, though other things have been an issue I have not seen a consistent fuel economy lately.

[falconfxr]

Ok, sorry I have been so long on a response here. I went on vacation and was able to leave my VX, now dubbed "little red" by my daughter, with my typical mechanic for the week. His determination? "I didn't feel much. Without being able to hook up a scanner to see the parameters, I'm really not sure. Maybe check the TPS." Epic Fail.

However, there is hope and possibly light at the end of this tunnel. I have spent a ridiculous amount of time reading blogs, articles, and most importantly the factory service manual looking for answers. I have reached a couple firm conclusions and a couple theories as well.

What I know for sure:

1. This is a chronic problem. Just Google "civic vx hesitation/stumble" and you will have hours of reading case after case of similar posts without any real conclusions.

2. Honda really should have just made separate FSM's for the Z series engines. It would have made this much easier than sifting through the footnotes about what does or doesn't apply to Z1 engines.

What I think:

Ok, this is where I'm seriously just theorizing right now. I have parts on the way to *hopefully* put some of this to rest. So, after reading the theory of operation for there lean burn function, open and closed loop sensors, integration of an EGR system on a lean burn engine, and even a Berkley University study from 1993, I paid VERY close attention to what was happening on my commute home the past two days. I found that at highway speeds, I was personally to blame for at least 50% of the problem. Once I got in tune with when lean burn was kicking in, when both intake valves were opening, etc. I was able to change how I managed the throttle, which DRASTICALLY smoothed out the "stumbles".

The hesitation/stumble is definitely the transitions to and from lean burn. Armed with that, I headed to the FSM:

According to the FSM, the control mechanism for VTEC-E's lean burn system is a constant monitor of engine speed, vehicle speed, water temp, and engine load. Notably, engine load is judged by intake manifold negative pressure. This is where I got to thinking about a couple posts about how people (and mechanics) clean out EGR valves and foam the manifold but don't really get in there and get the carbon build up really cleaned out. and for a car like mine, with nearly 245k, there's probably more carbon than open space for air to move. SO one of the parts (much to the dismay of my wallet) on the way is a new intake manifold. I know there's a way, posted on this site, about drilling into it and cleaning it out, but trust me I would have messed that up.

So, once the ECU receives its info that the parameters are met for changing the valve timing, it sends a signal to an oil pressure driven spool valve located within the head. The spool valve puts pressure on/off a timing plate on the primary rocker arm, which when activated effects different lobes on the cam, thus opening the second intake valve to full height.

This is the process that is creating the hiccup. I'm starting at the beginning, hoping that the pressure difference in the new manifold is enough of a change. Otherwise I will have to start progressing toward components within the engine, which is not something I really want to to!

Sorry for the ridiculously long post. Thoughts?

[falconfxr]

Got a call today...apparently there are no longer parts suppliers for intake manifolds for the D15Z1. Anyone know a supplier or have an effective cleaning method that doesnt involve drilling holes in the manifold? (please don't say seafoam ;-) )

[trollbait]

Since you were willing to replace the manifold, I'd say taking it off, scrub/scrape/power wash off what you can, and then soaking it in diesel/kerosene/gasoline/other solvent to hopefully get the rest of the gunk. Perhaps a shop with a parts cleaner, which pumps the solvent over and through the part or an ultrasonic water and detergent one, is willing to help out there. Then you don't have to deal with dirty solvent afterwards.