Team,

At 255K miles, my '93 Si manual is feeling its years, but I want to keep her alive for my kids to drive soon (I get a lot of requests to sell her). I now have a crank-no-start condition which puzzles me, so I've come to the oracles for divine advice...

Short version: It cranks fine, but often just won't fire. Other times, it fires just fine. Once started, it runs just fine. No start condition becomes much likelier after rain.

Long version ('cause Ive been dealing with this awhile, and have tried several fixes):
- It's an old del Sol, always parked outside, and the roof leaks when it rains. Since I live in California (where rain is scarce and precious to us), this leaky condition is fairly easy to live with.
- For a time, I had an intermittant crank-no-start, which occurred most often after the engine was warm and I turned the car off for a short time. Wait a few hours and it starts fine again. I feel that I resolved this by replacing the main relay (behind the fuse panel near above my left foot). I inspected the old relay and didn't find any cold or cracked solder joints The problem was solved (hurray) for many months, until it rained...
- I could often overcome this problem by popping the hood and wiggling a few things (then it would start fine). Eventually I determined that the most valuable part of that exercise was slamming the hood closed.
- I've been traveling for work a lot lately, and it's rained heavily a few times while I've been gone, so I haven't been able to open the windows to let everything air out (my usual fix). My daughter called me to tell me that my radio was on, and the car was "all steamy and drippy inside" (oh, joy). We Facetimed and I can confirm that the radio was on with the ignition in the off position!
- I have recently replaced:
-- the main relay (that worked until rain began)
-- the distributor (the whole thing, and then later the coil)
-- the oil temperature sensor
- I have checked:
-- battery voltage (it's good)
-- spark at spark plug cable - no spark
-- spark at ignition coil - no spark
-- power at lead from ignitor to coil - both leads(?) illuminate my test light (connected to chassis ground)
-- every damned electrical connector I can reach under the hood - they all looked clean and I added dielectric grease to them.
- I suspect:
-- maybe the new main relay is (already) bad?
-- I have a loose connection somewhere.
-- something in the electrical logic of the car is disabling spark.

Got advice for me?

Ken

 

Sounds like a faulty starter to me.

 

The starter motor? It cranks just fine, and that's what the starter motor is supposed to do. Is there another thing called a starter I'm clueless about?

Ken

 

Just because it cranks fine, doesn’t mean it will fire up the car. The starter solenoid could just stop sparking to tell the car to start. On my old car, I could tap the starter while trying to start and it would fire up. I eventually got a new starter and it fired up just fine.

 

Test your main relay and look for signs of water in the fuse box. You have to fix the roof seals somehow.

 

I am going to vote main relay, if that checks out, fuel pump, if that checks, failed capacitors in the ECU. We are talking about a 30! year old car now.

Do you hear the fuel pump prime with key on?

 

Update (I've been traveling a lot for work, plus Holiday madness and unusually frequent rain on my ungaraged car - hence my slow pace):

1) I have determined that I do not have fuel pressure (no flow at fuel filter).
2) I have replaced the main relay - no change. The (less than a year old) "old" main relay looks to be fine (no water signs, no bad solder joints).

This points me towards either a bad fuel pump or a bad ECU. I have mixed and incomplete directions for testing wiring to main relay to determine whether the bad signal is from the ECU. Can anyone point me towards a good source for this assessment (e.g. "the green wire with the yellow stripe should receive 12V when key is switched to _on_ or _start_ position; if not, then the ECU is at fault. If the white wire with the red stripe gets 12V in _on_, then the fuel pump is the problem.", or something like that)?

I'm hoping it's not the ECU -- that seems to be an expensive part to replace (but I see examples of self repair primarily by replacing aging capacitors on the ECU main board, and that's within my skill set). Of course, I'm also hoping it's not the fuel pump -- although that's a cheap part, one must remove a lot of paneling behind the seats to get to it...

I have applied Shin Etsu silicone grease to my door seals. I'll repeat this after a week or two to see if it helps to recondition my aging seals and reduce leaking in the rain.

Thanks for the advice thus far! Please keep it coming!

Ken

 

 

Thank you!

I realized that the "no spark" _and_ "no fuel pressure" almost certainly had a common cause, leading me to further investigate the Main Relay and Engine Control Unit... and today was sunny.

Main relay investigations were painstaking -- with my back contorted and head inverted to view the area behind the cabin fuse panel (and my feet in a puddle) -- and I didn't find anything apparently wrong (although my understanding remains incomplete: is the fuel pump always hot and then grounded when enabled?).

Ah HA!!! (I hope): inside the ECU, capacitors 15 and 19 show signs of leaking and corrosion! Those are both 33uF, but I might as well replace them all. Where can a purchase a set of these? My ECU bears that labels "37820-P28-L01; 762-200633" and "deshigiken Y ARP". There are seven cylindrical capacitors on the power side of the board. The board bears the labels "denshigiken", "02D01720-1500", and "A8Y-D". There are several unoccupied pads on the board (perhaps significantly) including the 27256 28-pin chip, which I've seen Youtubers indicate when describing their ECU as "chipped".

The inside of the ECU shows no signs of water damage, despite the recent soggy state of the upholstery. It appears that the entire interior of the ECU was spray coated with a lacquer.

Ken

 

https://www.hamotorsports.com/products/capacitorset

 

I believe the fuel pump capacitor is C14 and the link from above does not include C14 capacitor. This is the biggest capacitor on the board.
When you turn your car to "ON" position, do you hear your fuel pump priming?
fuel pump priming "supposed" to happen within 2 seconds of ignition switch being on "ON" position.

Fuel pump priming noise if pretty noticeable, if it's hard to hear, you can remove the bottom of the rear seat, which has the fuel pump right underneath it.

Also, just want to make sure, your ECU is not chipped, correct?

EDIT:
If you don't hear your fuel pump priming, try:
1. wiggling the ignition switch
2. give some love slap on the fuel pump panel.
3. rare but sometimes if your ECU has intermittent issue with capacitor or other chip contact issues, just keep waiting while key is turned to "ON" position for a good while. (up to about 30 seconds) and when the fuel pump finally primes, you can try to start the car.

no point of cranking the car, if your pump is not priming, no fuel, no start.

 

Team,

Back to rain and travel -- it will be at least week before I can offer another update.

- I have ordered a set of capacitors and intend to replace them all.
- I have researched the Engine Control Unit a bit more, and am confident that I have a "virgin P28" (the older 1720 version).
- I have no fuel priming noises, and neither jiggling the key nor waiting helps. I haven't yet removed all the panels I need to be able to manhandle the fuel pump.
- I think the silicone grease on door seals has reduced the rain ingress, but not yet eliminated it; I will re-apply in a week or two.

Ken

 

Team,

It's time for the next update!

A week later, the capacitor kit arrives and I replace seven in my P28 ECU. I reconnect the ECU, turn the ignition to "ON" and I hear the fuel pump priming! The first start is quite rough, so I let things warm up for several minutes before cycling ignition, and am able to restart the car normally multiple times afterwards.

Until the next morning, when I get no fuel pump again! A bit more (essentially lucky) research, and I get another hint: a deteriorating IC17, located next to C24 and C21, is known to interfere with pump priming _when it is cold_. I brought the ECU inside to warm up a bit, take it back out to reconnect, and the car starts again with no difficulty. IC17 appears to be a simple integrated circuit from Toshiba (part TA8903SN). I can get these from Ebay.

So, I'll replace IC17 next (in a week or so). Any other advice?

Ken

 

Maybe try reflowing the solder before you replace it.

 

I think you are on the right track... replace IC17 and you will likely be just fine after.

 

Team,

I'm back in town without good news. Replacing that chip was harder than I thought it would be, so it's possible I did more harm than good... I used up a lot of desoldering wick to free that 12-pin gizmo, and may have scorched something else in the process. Sadly, I'm back to crank-no start-no fuel pump prime. I'll tinker some more with the ECU, but it may be time for me to look for a replacement. Mine is a "37820-P28-L01", and I haven't been able to find one of these in my online searches. I do see "37820-P28-L00", and I understand that the last digit is a "version number". I'm not seeking a "chipped" variety, just something that will replace my existing unit. I expect that "new" will be absurdly expensive, so I'll be happy with "refurbished"; if necessary I might settle for "used and tested".

Any advice for a good source for these? Is that last digit really important?

Ken

 

I see one site selling a p28-L01 for $505. Guess I need to check what I have.

 

Last digit is not important.
Just make sure it’s an OBD1 P28 and auto/manual ECU. Auto and Manual is only 1 resistor placement difference but if you don’t want to mess with the board, you have to get the correct one.
Manual and Auto ECU can be converted to vice versa but definitely not the same.

You said you did not want the chipped variety but, if you want to tackle the soldering again, it might be cheaper to get an OBD1 ECU and chipping it for your engine.
Best advice on using the desoldering wick is to use generous amount of flux with the wick. W/O flux it’s almost impossible to completely desolder joints.
I’ve done this fairly recently for my car. I have the P05 (CX ECU) that’s been converted to P28 and chipped (emulator). Link below
https://honda-tech.com/forums/honda-.../#post52672057

If you don’t mind, you can post or PM me the pic of your board, and I can take a look to see if it’s still salvageable.
P28 ECU is close to $250 for an used auto. Manual is $300+

EDIT: seems like ebay has auto below $200 and manual ~$250

 

You couldn't be more wrong. L01 is a California emission specific ecu and it is very important.

 

ah ic. didn’t know that. thanks
now i’m curious what the difference between the tunes are.
also, what do you guys do with smog on an engine swapped car?

 

The lacquer sheen you see on the board is likely conformal coating which "is a thin polymeric film applied to a printed circuit board (PCB) in order to protect the board and its components from the environment and corrosion".

Probably wouldn't hurt to add some of your own when you are done.

 

Update time: Still no start (cranks, no spark, no fuel pump prime). I got some additional advice from a friend-of-a-friend mechanic and have investigated:
- electrical grounds in engine bay (all that I could identify) - no faults detected
- electrical connections at ignition switch - nothing cooked, everything has 12V when key is in some position
- electrical connection from ignition switch to cabin fuse box - nothing looks wrong
- cabin fuses - nothing blown
- inserted jumper to connector near ECU (it should flash the check engine light to display codes) - no codes
I'm now thinkin' bad ECU... I did just find a P28-L01 on EBay (~$300, not rebuilt, tested in a car) and ordered it. Wish me luck!
Ken

 

I would double check the ecu connection, unplug all 3 and reconnect if you haven't already. Could be some corrosion in there if you've had water in there.

 

Thanks, Chris. I did examine the three connections, and reseated them multiple times. No signs of corrosion, and no bent pins. I'm also fearful that the wiring harness may have a failure somewhere along its length, and that would be awful to diagnose. Ken

 

Progress -- even likely success!
Replacement ECU arrived yesterday; installed today. Engine starts and runs!
It will take me an hour or two to put the car back together and clean up. I need to update the tags (it's been non-op for months, now) and give it a proper test drive.
I couldn't remember how to install the ECU! It had been apart for so long... I tried it ten ways until one of them seemed to fit right. One panel screw has vanished mysteriously...

Ken