Troubleshooting the CRX
 

Okay, I've got three main issues right now, only one which POSSIBLY affects MPG. 1989 CRX DX, stock 1.5L motor, automatic.

First - seat belt not fastened light will NOT go out. I have shorted the wires together to no avail. It blinks constantly.

Second - fuel gauge is not accurate. It reads beyond full most of the time, only occasionally (at about 1/4 tank) reading right, then goes back up. New fuel sending unit is about $300. The previous owner told me that started when he "hit a HUGE speedbump at the airport." Judging by things, at high speed, too. I believe there is an access port in the bottom of the trunk to get to the fuel tank? Anything that can lube this? Likely a 20 year old fuel sending unit and it's a little corroded likely.

Third - tachometer usually reads double the actual engine speed. Can fluctuate without affecting engine speed. Brand new distributor, and I've been told that the engine speed sensor runs off the distributor, but don't have a Helms manual for the CRX yet, so I don't know if this is correct.

Anyone have any help?

As far as I know, that's a user status light only. If you don't want to bother finding/fixing the sensor that is (incorrectly) saying you don't have your belt plugged in, you could always disconnect the bulb (or wire leading to the bulb) to cut off that little annoyance.

And as an added bonus (of disconnecting the light), you will probably save a couple of watts of power (and therefore slightly better FE). Remember, older cars (such as the CRX) used incandescent lights for indicator bulbs (i.e. that was before the time when energy efficient LEDs were used for such indicator lights). And even very small indicator lights can easily be 2+ watts each. So while it won't make a big difference, disconnecting the (not wanted) warning light will also save a little electrical power, and therefore also give you very slightly better FE (due to slightly less alternator load on your engine).

FWIW: In my 1991 CRX, I have two seat belt plugged in lights above my rear view mirror (that's the way the car came stock, and I always hated those lights). And naturally, the passenger (seat belt) light would never go out, except when I actually had a passenger in the chair (and their belt was on). I put up with this for years, until I finally figured out how to open up that area, and disconnect the wires (which in that case was easier to do, then getting to the bulb itself). Now I no longer have to put up with that light producing glare, and I even saved a little power (i.e. very slightly better FE) as a result of not having that light on constantly.

Ouch. Have you considered trying to get a used part at the junk yard? Of course, the other option is to just work around the problem, and ignore the fuel gauge.

IMHO The easiest way to go without a (working) fuel gauge (and in the past I have), is to always fill up the tank (when you do get fuel) and always reset the trip odometer when you fill up the tank. If you do both of those things, you can easily tell how many miles (or kilometers) you have driven on the tank of gas, and that will give you a good idea as to how much further you can "safely go" before getting more gas (because it's easy/trivial to estimate the safe distance/tank, by knowing your car's FE and your car's tank size).

And you could also work around your stock fuel gauge, by building or buying a FE computer (since FE computers know how fast you are using up fuel). For example, you could buy/install a supermid for less than a new stock fuel gauge, or (for even less) consider building/installing that DIY FE computer being actively discussed on another FE forum (sorry, I don't have that other forum link right now).

After all, if you calibrate a decent FE computer, you can use the FE computer as a much more detailed/accurate "gas gauge" than any stock gas gauge is likely to give you anyway. So personally I wouldn't spend $300 for a new gas gauge, when I could get/install a FE computer for less than that cost, and the "fuel gauge" would be only one feature of the FE computer (the real time fuel use display being a much more valuable feature of the FE computer)...

This is the only one likely to effect FE much, so you might want to try getting it fixed.

The reason this might affect FE, is that I'm pretty sure that the ECU uses the pulses (that the tach also uses) to measure engine RPM. And, in turn, that engine RPM number factors into how the ECU controls the fuel usage. So if the ECU has a way off (off by a factor of 2) estimate of the RPM, the ECU might be doing some very unfortunate things as far as fuel usage goes...

There aren't CRXs in junkyards around here, period. So can't get the fuel sending unit. The unit WORKS - it just seems to be stuck on full - I would rather use the current unit & lube it properly so it floats right. I already know how to use the trip odometer, but with my mileage above 40 I may be able to squeeze 50 out of it on the highway. At those mileages, the fuel gauge may come in handy. I want to fix it.

Don't want to undo the dash to get to the seat belt light. It's on the dash, not the overhead. Overhead I'd undo the cover & remove the light.

See my gaslog & mileage figures - if it's doing ANYTHING to the mileage it's upping it, so that's why I need info on the tach setup.

You have the door-mounted seat belts, right? Honda moved the belts to the doors in most of the '89 models, and all of the '90-91 models... The idea being that you would leave the belts buckled at all times and just slip in and out of the car under them. It's stupid, but it satisfied the passive restraint requirements at the time.
Anyway, the seat belts, being safety devices, have to lock their belt retractors under certain conditions. You would not want those conditions to occur when you're swinging a door open or closing it, right? So, Honda added a solenoid to each retractor (2 per door) that, when energized, prevents the lock from activating. These solenoids are controlled by a switch in the door latch... The net effect being that the retractors won't operate when the door is open.
It would obviously be a bad thing if a solenoid were to get stuck in its unlocked state - the retractor wouldn't lock in an accident, rendering the seat belt useless. To deal with that, Honda added a warning system which watches the door switches, seat belt buckles and each solenoid via switches, among other things. If the system picks up an abnormality (door open, stuck retractor solenoid, belt unbuckled, ect.), it alerts the driver in varying degrees.
Point being, your safety system is trying to tell you something.

You're off by close to an order of magnitude. Majestic Honda lists a new sender for $36.68. It's number 14 in this diagram.

Yes, there's an access plate. It's under the storage bin behind the seats... The wiring to the fuel tank (for the level sender and pump) runs through it. The factory service manual actually starts diagnosis there. It says to remove the cargo bin (it should be held in by 6 screws), unscrew the access plate (3 screws) and unplug the electrical connector from the level sender immediately under the plate. Next, switch the ignition on (the fuel gauge should probably swing to E) and test for voltage across the two level sender wires... You should see battery voltage. Switch the ignition off and connect a jumper across the two wires. Momentarily switch the ignition on. The gauge should start moving toward F. The manual says to be sure to turn the ignition off before the gauge actually reaches F, or it might damage the gauge.
If the gauge passes the above tests, your problem is most likely the sender, as you've suggested. The sender is held in by a metal retaining ring that needs to be rotated to be removed. While my experience is somewhat limited, I have yet to come across a rusted retaining ring. I guess the sender area has been well enough coated with anti-rust gunk and is protected enough from the elements that it stays fairly rust-free.

Yes, that's right. More specifically, the tach signal is generated by the ignitor unit in the distributor. The ignitor (aka ignition module) acts as a middle-man between the ignition coil (which actually generates the high voltage to fire the sparkplugs) and the ECU (Engine Control Unit - handles fuel injection, ignition timing and idle control among other things). The ignitor unit switches power to the ignition coil on and off based on a firing signal from the ECU, and also judges the state of "charge" of the ignition coil, so as to avoid wasting power by overly charging or discharging the coil each time it fires.
Anyway, the ignitor unit also spits out a 12 volt pulse for the tachometer every time the coil fires. Failing ignitor units have been known to cause tachometer fluctuations, but it's usually in the form of the needle jumping around, not consistently reading twice the actual RPM.

The sender unit is just a float on an arm, a length of wire neatly wrapped around a cylinder and a contact that runs back and forth down the length of the cylinder, based on movement of the arm. It's a simple variable resistor really. Point being, it's all exposed to gasoline inside the tank. Any kind of lubricant you try to put on the sender would dissolve in no time. You might try taking the sender out and making sure the wraps of wire are clean and spaced apart properly, and that the contact is, well, making contact. Otherwise, just replace it.

i always thought the tach was run off the speedo cable? when my speedo cable broke i thought i remembered the tach not working either.

Nope. The speedometer cable is driven by a gear on the differential housing. If the differential isn't moving, the speedo cable doesn't move.
If you're not mechanically inclined, the differential is the part of the transmission that lets one wheel spin faster than the other (that is, when you're turning) while still applying power to both wheels. The drive shafts that run out to the left and right front wheels plug into the differential, so it's really the last part of the transmission as far as transmitting power goes.
Point being, the differential (and thus the speedo cable) only spin when the car is in motion. If the tachometer were somehow dependent on the speedo cable, it would always read zero when the car is stopped, even if you revved the engine.

If your tach really died when your speedo cable broke, I would suspect you have a grounding problem. I've heard of CRXs with grounding issues using the speedo cable as an alternate route (specifically, someone's speedo cable melting when they tried to crank the engine without a proper engine ground cable). If your gauge cluster's ground connection broke down at some point in the past, it's possible some or all of the gauges had been using the speedo cable as an alternate grounding path. If the cable breaks, you loose that alternate path as well, and the gauges stop functioning.

Okay - want to buy the fuel sending unit - can anyone tell me the difference between the two listed on Majestic's site? Vehicle is a DX, 1.5 engine, automatic.

One is made by Nippon Seikei, the other by Denso. Either one should work.

Thanks! Already have the fuel relay on order and the fuel pump too. Hoping to fix the "hunting" problem I have that also makes it shut off when I come to a stop sign.

To add, if the previous owner said that the fuel gauge started acting up after hitting a bump I'd look at the bottom of the tank for major dents that can effect the movement of the sending unit. The sending unit mounts under the passenger seats.

and the dash is easy to pull apart if you take time and keep everything in order and take pictures.