Pls help diagnose cranking no start

Started watching SD's classroom discussion of the operation of the PGM-FI. Seems that since the key was not in the ignition, the PCM power feed from the PGM-FI relay would have been off, so this gives me some hope that I didn't fry the PCM. Maybe I just blew a fuse.

Also, I'm guessing if I can get the engine running, any electronic problems will generate a code, which will make it easier to identify and track them down.

Don't sweat it- the relay is fused. Fuse 46 under the hood, and fuses 1 & 13 under drivers dash.

I really wouldn't even go taking the relay apart unless I saw an unexpected voltage while back probing it, that's up to you though.

TTW is right, I doubt you cooked anything expensive. The key was out, so you're safe.

Thanks guys. I was worried that I BBQ'ed pricey parts with that bit of boneheadedness.

Had a chance to try starter fluid. Actually, just before using the starter fluid, I tried to start the car normally (just to confirm I had everything connected back up - e.g., I had previously removed the connector to the starter's S-terminal so that I could use a remote starter switch during the compression testing), and the engine fired up right away, and then died a second or two later. Tried again, and it just cranks, no start. Maybe some residual fuel buildup?

First attempt using starting fluid (I disconnected the hose leading away from the air box, sprayed a few shots in, then replaced the hose, then started):


Second attempt:


So I guess this confirms what you all were suspecting - it's a fuel system issue. Next up, per TTW's suggestion, I'll check if the PGM-FI relay is sending battery voltage to the fuel pump on the BLK/YEL wire while cranking.

Also, I noticed that the CEL and immobilizer/key lights are not coming on when I turn the ignition to ON. From SD's video on the PGM-FI relay, does this indicate that the relay is not sending power to the PCM?

I suppose I can test this by figuring out which wire on the connector to the relay is supposed to send power to the PCM when the ignition is turned to ON, and then seeing if power is present on that wire.

jrud wrote: Also, I noticed that the CEL and immobilizer/key lights are not coming on when I turn the ignition to ON. From SD's video on the PGM-FI relay, does this indicate that the relay is not sending power to the PCM?

I suppose I can test this by figuring out which wire on the connector to the relay is supposed to send power to the PCM when the ignition is turned to ON, and then seeing if power is present on that wire.

Black/yellow feeds fuel pump power

Yellow/Black wire feeds PCM, Immobilizer (security), and all injectors B+ (fuse 46). Didn't you say you were concerned that you damaged the injector harness or may have shorted/pinched a wire? You might wanna check those 3 fuses i mentioned earlier before you go any further.

Also an FYI- the circuit that primes the fuel pump to start (fuse 13) is a different circuit than the one that maintains fuel pump power after the engine starts (fuse 1). :whistle:

So the plot thickens.

Last night is when I pulled the PGM-FI relay and connector down from its case and had that little dummy-you-forgot-to-disconnect-the-battery spark incident (key out of ignition).

Today's timeline:

• tried starting, it starts, dies in a couple of seconds
• tried starter fluid, it starts, then dies. Tried starting again and just cranks.
• added more starter fluid, it starts, then dies. Start again, then dies. Start again, dies very quickly. Try again and just cranks.
• the above is shown in the videos posted earlier today
• Checked fuse 46 - key out, and it checks good. I also pulled it out to look at it. Didn't look or feel like it was loose when I pulled it out.
• Checked fuse 1 - key to ON, and it checks good. I pulled it out to look at it. Didn't look or feel like it was loose when I pulled it out.
• Checked fuse 13 - key to Start/crank (engine starts and doesn't stall out! :blink:), and fuse checks good.
• Tried starting again, and it works.
• Tried again, and it works.
• Tried again, and it starts, then stalls out quickly.
• Tried again, and it just cranks.
• Tried again maybe 15 minutes later, and it starts and runs fine. At this point, I tried to induce a stall by shaking the PGM-FI connector, no luck, still running.
• Tried again, and engine is running fine. I checked for codes and there are none.
• The CEL and immobilizer/key lights are back on for a few seconds when turning ignition to ON.

As you can imagine, I'm happy and confused. My guesses/pure speculation:

1. there is a problem with PGM-FI relay, and the mere handling of the relay last night made a loose connection better?
2. fuse #1, while it tested good, doesn't look so great. Pic below, next to pic of a spare fuse I pulled from engine fuse box. Perhaps pulling out the fuse and reinserting it improved the connection?

I guess we can rule out the fuel pump itself as the issue? If so, then we know it's a fuel system issue, but that injectors are getting good signal (at least when I tested it - it could be that the 4 consecutive cranks I did to test the 4 fuel injector plugs for pulsed ground would have all resulted in the engine starting if those plugs were installed), fuel pump is priming and fuel pump is capable of running. So maybe it's a bad electrical connection? The relay seems like a good candidate, but unless the problem reproduces and gives me the opportunity to measure the voltage from the various wires coming out of the connector to the relay, I'm not sure how any definitive diagnosis of this relay can be reached.

I'll try to start again tomorrow, and if it starts fine, I'll try a few more times. If all attempts are successful, maybe it's worth taking out the relay (battery disconnected this time!) and closely examining the solder joints?

Obviously I'm open to theories to explain the pattern we're seeing and suggestions on next steps.

Trying to understand how the fuel pump is activated. When key is turned to ON, fuse 1 becomes hot and power is supplied to fuel pump to prime, which can be heard. Fuse 1 stays hot during cranking (per the wiring diagram I'm looking at). When key turned to start/crank, Fuse 13 becomes hot - what role does this play with respect to the fuel pump? Is it essentially an override that ensures the fuel pump doesn't get turned off by control circuits that turn the fuel pump off when it's only being connected via fuse 1 (e.g., if the key is left in ON position, but driver doesn't start engine)?

It starts! :woohoo:

I think you've got more than enough evidence to pull the trigger on a new main relay. Your handling of the relay itself very likely jarred it back into life temporarily, and that's why the symptom is now intermittent. Feel free to redo the solder joints if you like, but I'm pretty sure your local parts store will have several on the shelf. :lol: Probably multiple brands, too.

Tried again maybe 15 minutes later, and it starts and runs fine. At this point, I tried to induce a stall by shaking the PGM-FI connector, no luck, still running.

I've noticed the same thing on other failing main relays. :lol: For whatever reason, the relay only fails to engage once opened, and won't break the connection once it's engaged. Perhaps because the magnetic field strength needed to engage is more than what's needed to keep it engaged? :huh: It doesn't really matter for where you're at, just thinking out loud.

fuse #1, while it tested good, doesn't look so great. Pic below, next to pic of a spare fuse I pulled from engine fuse box. Perhaps pulling out the fuse and reinserting it improved the connection?

Maybe? I find that kind of appearance on fuse terminals to be typical of older vehicles, and not necessarily a sign of a bad connection. Unless you saw that the female terminals in the fuse box looked overheated, I wouldn't sweat it.

So it sounds like you had a bad connection either at the fuse or relay. That fuse looks like doo-doo. I would clean all the contacts for that fuse and the relay connector too, maybe put a little dielectric grease on them if you have a tube kicking around. Also just double check that the relay connector doesn't have any loose pins.

As for "how it works"... I pulled up the diagram, and I will try to explain. Much easier to explain in person, but here goes...

And please, Honda guys correct me if i'm wrong, I am just interpreting it as I see it...

The first diagram simulates a potential poor fuse connection that seems to have caused the issue. The yellow marker is everything that would be "hot" when you try to start it. Note the blue "x"- the PCM will not provide a ground there to energize the relay, because it is not getting a power input on the green "x"'s. This is part of the immobilizer/anti-theft protection circuit.




The second diagram is with everything functional, i have them in different colors just to see circuit separation easier. I think the confusing part is the wire i have circled in green. Because, doesn't it look like the yellow circuit should power up the other side of the relay? And then why would we need the blue circuit?

That wire circled in green has a resistor and a diode on it. That tells me that the purpose of it is to absorb flyback voltage, likely from the wire below that powers the injectors. With that terminating resistor on the circled wire, it wont have enough juice to power up the other side of the relay. Hope this helps.

Tyler wrote: It starts! :woohoo:
I think you've got more than enough evidence to pull the trigger on a new main relay.

Agreed. While I'm not certain that it's the relay and not fuse # 1, that fuse seemed fully inserted when I removed it (based on both how it visually lined up with the other fuses - it wasn't sticking out, and on how much force was required to pull it), so even though it looks crappy, I'd guess it wasn't impeding current flow to any significant degree. Plus we have lots of evidence from other Hondas that the main relay is often the culprit in a crank no start where spark and air/compression are present.

Tyler wrote: Your handling of the relay itself very likely jarred it back into life temporarily, and that's why the symptom is now intermittent.

If that's what happened, my guess on the specific part of the handling would be that using a screwdriver to pry the relay out its housing may have flexed the relay body such that marginal connection(s) were temporarily made better.

Tyler wrote: Feel free to redo the solder joints if you like, but I'm pretty sure your local parts store will have several on the shelf. :lol: Probably multiple brands, too.

I'm getting a new relay. When I get a chance, I will try to clean/wick/resolder since I have a decent Hakko soldering station and I could use the soldering practice. But with a long trip coming up, I'd rather not put my very basic soldering skills on the line!

When I swap relays, I'll post up some pics of the solder joints if there's anything to see there.

TheTechWhisperer wrote: So it sounds like you had a bad connection either at the fuse or relay. That fuse looks like doo-doo. I would clean all the contacts for that fuse and the relay connector too

I'll replace the old fuse #1 with the spare. And I'll be replacing the main relay as well. I've got some CRC QD electronic cleaner that I'll use to clean up the contacts on the old fuse and old relay (which I'll try to bring back to life with some soldering cleanup/reflow).

TheTechWhisperer wrote: , maybe put a little dielectric grease on them if you have a tube kicking around.

I do have some. Perhaps you can clarify my understanding of how to use it. I've only ever used it on spark plug boots, where it both helps prevent the boot from sticking to the spark plug (the obvious-to-me function) and to allegedly prevent arcing - I guess that could happen if the spark plug no longer sparks and the voltage is 'seeking' a ground?

So with your suggestion to put dielectric grease on the fuse and relay contacts, I take it that it will help prevent a stray connection, but at the same time it won't interfere/insulate the pin on which it is applied from the female connection the pin plugs into?

TheTechWhisperer wrote: Also just double check that the relay connector doesn't have any loose pins.

Roger that.

TheTechWhisperer wrote: The first diagram simulates a potential poor fuse connection that seems to have caused the issue. The yellow marker is everything that would be "hot" when you try to start it. Note the blue "x"- the PCM will not provide a ground there to energize the relay, because it is not getting a power input on the green "x"'s.

Ah, that blue X is something I was missing - I was only thinking that the hot-with-cranking fuse 13 meant power was getting to the fuel pump, but overlooked the fact that the control circuit isn't active without a ground! :pinch:

TheTechWhisperer wrote: The second diagram is with everything functional, i have them in different colors just to see circuit separation easier. I think the confusing part is the wire i have circled in green. Because, doesn't it look like the yellow circuit should power up the other side of the relay? And then why would we need the blue circuit?

That wire circled in green has a resistor and a diode on it. That tells me that the purpose of it is to absorb flyback voltage, likely from the wire below that powers the injectors. With that terminating resistor on the circled wire, it wont have enough juice to power up the other side of the relay. Hope this helps.

Yeah, that yellow circuit seemed odd to me. Thanks for explaining its function.

jrud wrote: If that's what happened, my guess on the specific part of the handling would be that using a screwdriver to pry the relay out its housing may have flexed the relay body such that marginal connection(s) were temporarily made better.

It may sound crude, but my go-to move when I suspect a PGM-FI relay problem is to slap the lower dash panel with my hand while cranking. :silly: Never fails to jar a marginal relay back to life. Customers don't like it when they tow their car in, only for you to drive it into your bay like nothing happened. :lol:

Tyler wrote:

jrud wrote: If that's what happened, my guess on the specific part of the handling would be that using a screwdriver to pry the relay out its housing may have flexed the relay body such that marginal connection(s) were temporarily made better.

It may sound crude, but my go-to move when I suspect a PGM-FI relay problem is to slap the lower dash panel with my hand while cranking. :silly: Never fails to jar a marginal relay back to life. Customers don't like it when they tow their car in, only for you to drive it into your bay like nothing happened. :lol:

LMAO! Talk about ego destruction! Customer gets to eat some humble pie while paying that tow bill.

I guess slapping works because the relay is in a housing that is mounted to a bracket - so slapping the lower dash panel effectively transmits vibration to the relay in a manner that wouldn't be effective if the relay were hanging and secured by zip ties/similar under the dash, as some of the other connectors are.

Any progress on this one? Not nagging, just curious.

Tyler wrote: Any progress on this one? Not nagging, just curious.

I got a new PGM-FI relay and swapped it in. I was going to wait a few more days to be certain that this resolved the issue. But I've started the car 7-8 times since the swap and it has started every time (though even the old relay was starting most of the time after I handled it a bit), so it's looking good.

The new relay (it is OEM Honda) is different from the old one (new relay on the right):



No obvious (to me) solder joint failures on the old relay:



All the youtube videos I've seen on failing main relays pointed out cracked solder joints. Have you guys seen these main relays fail without obvious solder joint issues?

I can't say I've taken apart any of the PGM-FI main relays I've replaced. It's possible that your old relay had failed/high resistance load contacts, which would cause the same problem. Or, the relay coil winding was going open.

Either way, it sounds like you fixed it! :woohoo: The relay just chose to start failing while you were doing your unrelated repairs. That's how it goes with older vehicles. :silly:

Tyler wrote: I can't say I've taken apart any of the PGM-FI main relays I've replaced. It's possible that your old relay had failed/high resistance load contacts, which would cause the same problem. Or, the relay coil winding was going open.

Either way, it sounds like you fixed it! :woohoo: The relay just chose to start failing while you were doing your unrelated repairs. That's how it goes with older vehicles. :silly:

Yeah, it certainly does seem like the problem was the old relay. I'll have a few more days prior to a long road trip to use the car and build up confidence that it will start 100% of the time.

Thanks to you and TTW for helping me diagnose this. I definitely learned a lot along the way, including how useful a can of starting fluid can be, and how I shouldn't automatically assume that any issue that arises after repairs/maintenance must be related to that work.

Happy to!

...and how I shouldn't automatically assume that any issue that arises after repairs/maintenance must be related to that work.

This is one of the hardest things to learn, especially as a professional technician. :blush:

It may sound basic but is there fuel in the tank ? Other thing to check for is any vacuum hoses disconnected.