92 Civic VX stumbling/hesitation

[mrmad]

Originally Posted by 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 ;-) )

To get my CRX's EGR ports clean I sprayed carb cleaner into the ports while the engine was running. I would squirt a little at a time, hoping it would soften/loosen up the black soot that was clogging the ports. It did eventually work. I was careful not to put too much in there at a time as I was worried about the fire hazard.

If this didn't work, I would think if you removed the IM, you could spray carb cleaner from both sides.

[add|ct]

I like spraying a combustion chamber cleaner 'foam' type product and letting it soak attached the vehicle, no experience cleaning removed. It mainly cleans the piston heads but can also clean up some of the EGR system during the soak. I currently prefer Amsoil's Power Foam since its reasonably priced and a larger can than other products. Does the job.

Otherwise, manual cleaning it is.

[N2UAD]

For me cleaning the intake manifold gave me the biggest improvement. I don't recall all the steps but I did not have to drill out and tap those spots on each runner. Although it would not be hard to do.

If you don't think you can drill and tap then take the manifold to a machine shop and have it done. Or better yet take it to a machine shop that has an ultrasonic cleaner.
Mine was so crudded up I don't think much was getting thru.
So my advice is to take it off and clean it up. I'm sure I used carb cleaner and brake clean.

One thing I do remember thinking while I was cleaning: There is no way all the crud will get removed by a foaming cleaner while on the car. Even if the foaming cleaner did work it would release a boatload of gunk that does not belong in the engine.

I did all the same reading you did and came to the same conclusions. You are on the right track!

[VXonFumes]

I'm new to this forum also, but this is quite the band of brothers! I also have a Canadian, 1992 Civic VX with, guess what...stumbling/hesitation issues, same as most here. I've had lots of honda's in my life and there is so much potential with this VX but man is it a pain in the butt when it doesn't work perfect.

I don't have time to give a full post here, but we should pool our resources and make this the definitive thread on this issue. I got my car almost 3 years ago, completely gutted the car so I could put new quarters on and make it look new. Found out out the tranny main bearing was gone, so got a remanufactured tranny from a place in Cali called "Syncrotech," who specialize in manual honda trannies. For 600 bucks I got a remade tranny better than new b/c they polish all the innards with ceramic media too. But a month after I got the car and sunk this money into it I got layed off!. No money, and the car sat for more than two years (aside from starting it periodically). Not good. This spring I wanted to drive it to Atlanta to save gas but couldn't get it past emissions. 900 dollars later and a couple shops trying to find the issue...it's past safety and emissions (barely...we cheated).

Something on these VX's deteriorates with time, and like someone else said, they were so rare and sufficiently complicated and different enough that no one even at honda really knows anything about them. (Sort of like my 90 prelude with four wheel steer...no one knows how to do that at honda anymore either.)

In short, my car has 288,000 kms on it, and I just drove my first full tank and got 814 kms on 38.4 liters of fuel...I think that's 44 mpg. What a disappointment! It should be getting 55 mpg at least if in good tune. I know a honda mechanic who knew someone who had a VX back when they were new, and under the perfect slow freeway drive could get close to 70 mpg. I believe it could do it. I managed to get 930 kms on one 60 liter tank (36 mpg) on our 98 honda odyssey last summer while fully loaded all 6 of us and our luggage going to the cottage...with several tricks like LRR tires, air-tabs and the best quality, thinnest grade Amsoil lubes in everything in the van, and other tricks.

Oh, by the way just let me get this out of the way right off the top, b/c I hear guys like me getting slammed on other forums. I am an Amsoil Dealer in the Niagara Peninsula in Ontario, and I will sell Amsoil anytime, anywhere, to anyone. I've been using the stuff for 10 years, have done many oil analysis reports for customers and fleets, both gas and diesel, and I've seen phenomenal results. There is nothing better money can buy for lubrication (or for lubes that improve mileage). That's my biased opion. So now the secret's out, if you want to hate me go ahead, buy whatever oil you like it's a free country, but at least I'm not hiding what I do for a living here.

I've changed plugs with NGK ZFR4F-11 (very important), NGK wireset, new distributor rotor, cap, full fuel system clean with a motorvac, new fuel filter, fresh gas, new timing belt and valves adjusted, and all such typical tune-up items. I even took the intake manifold off and drilled it out and cleaned it out. What's really frustrating here is that while on the outside it looked old and used as you'd expect, the inside of the manifold was totally clean! I mean, I am wondering if someone put on a new manifold just before me, but can't be b/c the screws that hold on some of the sensors are old and rusted. An unsolved mystery. I also used Amsoil powerfoam, but you really need to take it off the engine and do it manually if it's plugged. It is a pain though.

With my car it's definately a closed loop issue: when just started it pulls much smoother and stronger. When warm and in closed loop it has excessively lean burning symptoms very often; way more than any engine should. It hesitates/stumbles and has significantly less power than it should have...I had a 1.3 1985 civic that probably moved as good as this VX does now. With 92 horse, a pile of torque down low and only 2100 pound car, this VX should pull nicely but it's pretty gutless overall. And hesitation/stumbling makes drivability worse.

Hopefully we can find a cure. I'm confident we can...there is a mechanical cause *somewhere* but it's a bugger to find. Something is making it run too lean somehow. I had it on a dyno at one shop and when they injected a little propane into the airstream before the engine, the power surged and it ran much smoother. As these cars age, something is getting tired or crossing signals, either the grounds, or the sensors, or perhaps the ECU itself, vacuum leaks, or perhaps a combination of these. But it is running in an air/fuel range that is not quite right. This seems to be the best general theory I can come up with that matches most stumbling/hesitation symptoms listed all over the web for this engine. Difficulty is that there are so many things that can contribute to this.

Falconfxr in a more recent post you were describing the mechanics of v-tec engagement, not lean-burn initiation: I don't believe the two are joined at the hip, although perhaps they are connected somehow in this engine. V-tec engagement is somewhere around 2500 rpm on the VX, very low for a civic, but my engine has the stumbling blues much lower than that too.

I found one thing that slightly helped mitigate the symptoms, but I don't really understand how. I put premium gas in and it helped stiffle the stumbling/hesitation slightly, but I was pretty sure the manual only calls for regular gas. Perhaps the other gas was getting too stale, or perhaps (I'm not sure here) certain lean-burning conditions contribute to knocking a little more and the higher octane would help stabalize combustion in such a condition. But don't quote me on this. If premium helps you a bit great, but if so it will only be a bandage and not address the root cause.

I'll check back from time to time, see if any of you have any success and post my results also. I have several things I still want/need to do so it's premature. By the way I have the full Honda Service Manual on PDF in case you don't. But I'd have to upload it if you want it and it's around 60 Megs I think. Don't know if that will work, forgot where I got it from.

Thanks so much to all you guys for trying so hard to fix this common migrane headache. To quote Eric the Car Guy...Stay Dirty.

John

[VXonFumes]

Hi all, just needed to post a correction form my last long post. The first tank I got just shy of 50 mpg, not 44. I guess I can't do math very good.

I put high octane in the second tank and got 51.12 mpg on that tank (just over 900 kms). But the increased mileage could be anything: more highway driving, or the car could just be slowly clearing itself out after sitting around for 3 years. Actually this whole tank was run with an exhaust pipe leak under my seat (waiting for the part to come in)...and normally that would not help a small car with mileage as little cars need the extra torque down low that exhaust back-pressure creates.

But it seems to be improving slowly, running better slowly, and the mileage isn't so bad anymore, so I can't complain very loudly anymore. However, I am still going to be embarking on a total mileage campaign but I need money first.

One last thing I wanted to mention to some guys who get rather horrible mileage in their VX's, is that they need to be bone stock, OEM. I think a lot of them got modded by young kids who wanted them to go faster, but that will destroy their mileage potential. Intake, exhaust, wheel sizes, spark plugs, ecu's etc all need to be stock OEM for high mileage.

I'll update things if they progress significantly.

John

[theholycow]

With a 2% difference between tanks, that's as close to exactly the same as you'll ever see apart from coincidence. Don't read too much into it.

It is my understanding that it's not the backpressure that helps make torque, but rather the exhaust gas velocity...the backpressure, while usually present under those conditions, is not a functional part of the equation.

Anyway, great job with the fuel economy on what sounds like a car that was rotting unused for a while!

[Lean Burn enthusiast]

Reading through this post I realized that I've been quietly benefitting from all kinds of hard-won (& generously shared) info from this site for the past few years. I happen to believe that every VX can & should be brought back to as-new functionality...so it seemed like it was time to join gassavers.org & start paying it back -- or is it paying it forward?

****
Up here in the Green Mountains my friends & I currently have a total of (5) '92-'95 VXs that are used to commute as frugally as possible. (There would be more if we could find more of these lean-burn unicorns of the Civic herd.) Over the past year we've added (4) '00-'01 Honda Insights to the mix. Although I work on military avionics at the day job, we've spent plenty of time in the evenings sorting out driveability/MPG issues on these lean-burn commuter cars.

But I digress. For what it's worth here's what we've learned about how to sort out driveability issues on these lean-burn vehicles. NOTE: The following info is only of value when you are faced with a car that drives fine in open-loop mode, or even closed-loop normal (stoich) mode, but still manages to drive poorly in lean burn mode with no error codes. (!)

Before performing the following checks, it's assumed that all the normal wear items have been proven-good (plugs/wires/coil/distributor/base timing/timing belt/vacuum leaks/IACV cleaning/MAP/no LAF codes/fuel filter/all engine & ECU grounds cleaned & tightened/etc) ...and although there's no codes, you are still fighting light-throttle lean-burn driveability issues. So what now?

1) If you have ever experienced a noisy volume knob (potentiometer) on a stereo, then it will come as no surprise that a worn/scratchy Throttle Position Sensor can play havoc with closed-loop operation while reporting driver requests to the ECU. More so than normal cars, a VX with 250K miles on it may have spent 90+% of it's time with the wiper on the TPS potentiometer sitting in the same spot while the driver is cruising for max MPG on the highway. Like all mechanical items, the TPS only has so many wipes in it before it starts delivering intermittent resistance values. (ie: the scratchy sound in the volume knob on the old Fisher preamp.) This 'scratchy' feedback will disrupt the ECU; instead of scratchy audio, you end up with hesitation/stalling/etc. FWIW, we never change parts speculatively -- instead we use a DVM to measure the resistance of the TPS while we s l o w l y move the throttle from idle to WOT. (Of course, engine off, harness disconnected.) IF the resistance changes smoothly with no hiccups across the range, then move on to the next troubleshooting item. On the other hand, if you find a spot where the resistance doesn't track linearly with the travel, then a new TPS sensor is the fix.

2) Check the ECU for water damage. Why? Google Honda Service Bulletin #92-050, for the '92-later Civic, which discusses water ingress due to inadequate seam sealer on the inner fenders at the factory. I've got photos showing where water had dripped into the ECU (with corresponding burned components on the module) ...and this was the root cause of why the closed-loop driveability was so bad on a high-mileage FL VX that I bought on eBay. (The only way I was able to drive it back to VT was to pull the VSS connector and throw the car into limp-home mode, where it ran reasonably well for the remainder of the road trip, but at the same time only delivered 25 mpg, while the chase car (a healthy VX) delivered exactly twice that.)

3) Assuming that the TPS sensor passes the resistance check & your ECU is clean & dry, the next thing to verify is that you have the correct 5-wire 'O2' sensor. (Actually, it's a LAF {Linear Air/Fuel}, but it seems that only the folks in the lean-burn community are familiar with that acronym.) It's not fair, but the ONLY 5-wire sensor that is guaranteed to work is the OEM (Denso) sensor that Honda installed at the assembly line. For the 49-state P07 calibration the Honda part number is 36531-P07-003. The DENSO part number that covers this Honda part # is 234-5052. The Bosch 5-wire LAF sensor may or may not work, which is a shame, for it is cheaper to purchase. As for the generic 5-wire sensors, they don't work more often than not. The Denso sensor from the local stealership is downright spendy, but this part is currently available on eBay for (only) $233. Our experience across the 5 VXs to date support the observation by others here & elsewhere that the Denso sensor gives good driveability -- anything else is simply bad juju, and to be avoided.

NOTE: What's unfair about the above is that you can have a non-Denso part installed, no codes are kicked, stoich operation is OK, but the lean-burn driveability is still flaky. (!)

4) Assuming that you have eliminated a scratchy TPS sensor, a watery ECU, or non-Denso 5-wire O2 sensor, it's time to perform a compression check. (Bonus points if you use a leakdown tester.) Assuming benign neglect (if you are buying a used VX) by the previous owner, the valve lash is rarely checked/adjusted. As the valve/valve seat wears, this tends to close up the valve lash. After enough miles have accumulated, during sustained high speed operation in hot weather, the exhaust valves are held ever so slightly off of their seats by the closed-up lash, and they start to burn, for the only time they get to sink the high heat of hot exhaust gasses speeding by is by quality metal-to-metal contact between valve face and valve seat. (And into the water jacket behind the seat.)

NOTE: When the valves are just starting to leak, the engine will operate OK at normal (stoich) air/fuel ratios...but when you go into lean-burn mode this leakage is just enough to ruin the driveability in lean-burn mode. (On the worst-case car that we've brought back, the 2nd intake valve inlet was completely blocked by carbon on all 4 cylinders -- with 250,000 miles on the clock, I don't know if the VTEC was ever engaged by the previous owner?)

****

Other fascinating VTEC-E trivia: In the VX, the VTEC solenoid doesn't engage nearly as often as some folks would lead you to believe. It's not just rpm, but rpm plus lots of demand by the driver. To understand the behavior once & for all, we installed a simple tattletale LED in the dash (into the blank where the clock is supposed to go) and then wired the positive side (through a resistor) to the VTEC solenoid.

After driving around with this for a few minutes all the mystery disappeared; basically you might get into VTEC mode if you are merging onto the interstate & you're pedaling furiously in order to avoid being overwritten by oncoming traffic. And yes, we left the little green LED in place as a geek conversation starter about the wonders of VTEC-E.

Cold-engine clatter on high-mileage Civics that disappears as the engine warms up? Assuming that the valve lash is set to specification, this is the sound of piston slap...especially if the clatter becomes more pronounced with more throttle, and almost disappears as you let off. As long as the oil consumption doesn't take off, these lightweight all-aluminum modestly-powered engines will clatter right along indefinitely with no reliability issues.

****
Hopefully the above will help anyone out there trying to revive a high-mileage VX for one more tour of duty. Owning both an '01 Insight (that will touch 70 mpg on the open road) and a '95 VX that will deliver 50+ mpg when driven smoothly (but no hypermiling in either case) I find that the Insight is a wonder of hybrid technology, but the VX is genuinely impressive by how well it gets the high-mpg job done for upwards of 300,000 miles w/no hybrid hocus-pocus.

The bottom line? We've yet to find a VX that can't be cured...and they really do drive nice when fully sorted out.

Apologies for the length, but if this helps others enjoy the VX at it's best then it was worth it.

Cheers --
dbm

[IndyFetch]

Well done.

[add|ct]

Does anyone know if a bad Intake Manifold gasket on these engines could let the coolant passage from the head to the IM leak into the runner for cylinder #4, the gasket failed there(or wasn't sealing properly)?

Like during high rpm, there would be enough vacuum to pull seeping coolant at a bad gasket right?(the coolant passage is on the lower corner of the runner for cyl #4).

Thank you. Trying to avoid pulling the head if another entry is possible. I do have a 2nd oil analysis, 5th since owning the vehicle in Jan 2010, first sign of coolant entry was this summer. I haven't overheated the car.

I suppose I could remove the cylinder #4 spark plug and check it/it's cylinder's head compared to the others. But I do not have an increase coolant consumption condition.

[VXonFumes]

Hey lean burn enthusiast: and I thought I was long winded. Your post was even longer! lol. But worth it. thanks for your post!!! We need more guys like you with lots of hands on experience.

Anyways, I just replaced a 20 year old manifold air intake temp sensor with a new one on my VX. (Old one was off by quite a bit and making ratio too rich.) I'll see how that helps drivability, although it has been slowly sorting itself out with driving.

Also just put in some Amsoil Signature Series 0W-20 oil & Ea filter, and installed a warm air intake with a superb Amsoil EaA oval shaped cone air filter with an Amsoil pre-filter over that. Basically 2.5 times the surface area of the OEM filter, and this filter medium breaths way easier than the OEM paper filter! Overkill I know, but it's the smallest one I could find, and can't get one made to fit in the airbox.

I also just installed some Nokian Hakka R's on the civic! They are ultra low rolling resistance tires & roll better than many all-seasons. Check out the rolling test video: The rolling resistance test of Nokian Tyres - YouTube The civic coasts very easily with these tires pumped up to max pressure.

Well, I'm still getting the car up to peak efficiency and working out bugs from sitting for 3 years. Slow and steady...the tortoise wins the race. I'll post results in time.

Anyways, just wanted to say thanks for sharing your experience, very appreciated. If I'm ever in your area (don't expect that soon) I will seriously try to look you guys up. Ditto if you are ever in Niagara Falls area.

take care,
John