M20 stall out, not main relay.

[quikveedb2]

On my way up to Winter Park my car stalled once very briefly on the highway, like a split.second, and carried on for another minute or 2 without issue. It stalled a second time, I downshifted, it caught & ran for a couple more minutes, stalled, downshift, run, stall, downshift, run until finally it just quit. I pulled off & tried to start the car, of ran for a minute sounding like it was only hitting on a couple cylinders, died, and refused to start again. The tach & other gauges worked the whole time, and the main relay was replaced last spring, so I doubt that's the issue. I replaced the fuel pump relay with a spare I carry & the car started right up, so out of curiosity I put the first relay back, and it started & ran as well. I put the spare back in & drove the rest of the journey no problem. Thoughts?

I have to drive back to Boulder tomorrow, so any input would be great.

[matt0300]

Sounds like ur cps is going bad.

[matt0300]

Or fuel pump.

[Violet88]

Sounds like ur cps is going bad.

[quikveedb2]

Tested cps a year or so ago, it was within spec, but I'll check it again.

[Adrian_Visser]

Just because you tested it a year ago doesn't mean it's fine now genius.

Also if it's an intermittent problem which by the sounds of it it is you are going to have to test it when it isn't working to find anything out.

Was the replacement main relay a brand new one or one pulled from a junkyard?

The relays (main or fuel pump) could still be an issue as well as the wiring on the relay mounting sockets.

When my CPS went earlier this spring I drove for an hour with my back seat up wiggling the fuel pump connector every time the car stumbled and tried to die. Ironically the car would come back to life when I did this, but the next morning when I went to start it it wouldn't do a damn thing and this time I thought to test the CPS and found it to have infinite resistance across its terminals.

Just saying sometimes you can't write things off as "tested good" too soon.

[quikveedb2]

Main relay was purchased new, and I didn't rule out the cps, I said I'd test it again. Have anything to contribute besides echoing someone's suggestion and a bit of attitude?

[7pilot]

Tested cps a year or so ago, it was within spec, but I'll check it again.

Open the glove box and take a sniff.
Does it smell faintly like hot electronics??

m

[quikveedb2]

I'll check, next time it acts weird.

[quikveedb2]

Also, cps tested @ 522 ohms which is within the 540+/-54 specification. It tested dead on at 540 when I tested it last.

Temp sensor, distributor cap, rotor, and ignition coil have all been replaced with new items in the last 2-2.5 years.

[jlevie]

If the tach didn't drive twoards zero when the engine misbehaved, the CPS, main relay, and fusible link isn't the cause. That leaves the fuel pump relay, pump, rusty tank, or C191 connector (on a 9/87 or later M20B25) as likely suspects. In that case you will usually see the econometer drive to zero in an event.

[Conki]

If the tach didn't drive twoards zero when the engine misbehaved, the CPS, main relay, and fusible link isn't the cause. That leaves the fuel pump relay, pump, rusty tank, or C191 connector (on a 9/87 or later M20B25) as likely suspects. In that case you will usually see the econometer drive to zero in an event.

This is helpful, because I have a similar issue. When the engine quits on my while driving, the tach slowly starts going down as the engine rpm goes down, so it means it's not the cps/main relay?
Since this is intermittent, I'm guessing it could be a sensor. MAF probably?
And I also think now that the engine only cuts off when there is no load on it (clutch depressed while approaching a red light, or just sitting at a red light in neutral). I'm not a 100% sure yet, but I'll pay attention to it, because then it could be the ICV probably?

[jlevie]

This is helpful, because I have a similar issue. When the engine quits on my while driving, the tach slowly starts going down as the engine rpm goes down, so it means it's not the cps/main relay?
Since this is intermittent, I'm guessing it could be a sensor. MAF probably?
And I also think now that the engine only cuts off when there is no load on it (clutch depressed while approaching a red light, or just sitting at a red light in neutral). I'm not a 100% sure yet, but I'll pay attention to it, because then it could be the ICV probably?

A decrease in the tach that follows the engine speed means that the DME is tracking engine speed. That, in turn, means that the DME is running and getting valid data from the CPS. Which exonorates the main relay, fusible link, CPS, and DME.

[quikveedb2]

Thanks jlevie, you're always coming through with good info. Car made it back to Boulder today without issue, with the spare fuel pump relay installed. I'll continue doing diagnostics as time permits.

[Dolmangar]

This is helpful, because I have a similar issue. When the engine quits on my while driving, the tach slowly starts going down as the engine rpm goes down, so it means it's not the cps/main relay?
Since this is intermittent, I'm guessing it could be a sensor. MAF probably?
And I also think now that the engine only cuts off when there is no load on it (clutch depressed while approaching a red light, or just sitting at a red light in neutral). I'm not a 100% sure yet, but I'll pay attention to it, because then it could be the ICV probably?

I had a similar problem that ended up being vacuum. I cleaned the ICV and replaced the plugs with no change, then I replaced the ribbed air intake boot ($20) and found that the breather hose on the valve cover was missing it's hose clamp (I traced the lines and made sure that all of the other clamps were in good shape.

Ended up pulling and cleaning the contacts on all of the relays just to be sure, but I don't think that made a difference as they were in pretty good shape.