1987 csx stumble

My daily driver 87 csx. The only stuff not factory stock are MP LM, roller cam, and no cat.

The issue is intermittent, but occurring more frequently. When accelerating, the car stumbles, barely accelerates, and pops out the exhaust. To me, it feels very ignition related, because of the exhaust popping. Yesterday, it blew out a sooty loud bang, so I'm leaning towards ignition or possibly over fueling. Under hard acceleration, it will produce boost and accelerate better, but not like it's normal potential and it's popping and miss firing the whole way. Suddenly it stops and drives normal.

No codes have been active. Tach, vacuum gauge read normal during this (not bouncing around) No other instrumentation is present.

So far I've tried from a known good 88 shadow a coil, pick-up coil, complete secondary ignition system. I have a drb2 and I'm seeing no values out of the ordinary, I've looked in the fuel pressure regulator hose for fuel, none found. I bypassed the baro read solenoid with no changes, double checked cam and ignition timing and they're correct.

I don't have another LM as a tester, as most of my stockpile is smec based

Any ideas? Other things to check or try?

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Originally Posted by shadow88

My daily driver 87 csx. The only stuff not factory stock are MP LM, roller cam, and no cat.

The issue is intermittent, but occurring more frequently. When accelerating, the car stumbles, barely accelerates, and pops out the exhaust. To me, it feels very ignition related, because of the exhaust popping. Yesterday, it blew out a sooty loud bang, so I'm leaning towards ignition or possibly over fueling. Under hard acceleration, it will produce boost and accelerate better, but not like it's normal potential and it's popping and miss firing the whole way. Suddenly it stops and drives normal.

No codes have been active. Tach, vacuum gauge read normal during this (not bouncing around) No other instrumentation is present.

So far I've tried from a known good 88 shadow a coil, pick-up coil, complete secondary ignition system. I have a drb2 and I'm seeing no values out of the ordinary, I've looked in the fuel pressure regulator hose for fuel, none found. I bypassed the baro read solenoid with no changes, double checked cam and ignition timing and they're correct.

I don't have another LM as a tester, as most of my stockpile is smec based

Any ideas? Other things to check or try?

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My dad just had similar issues on his GLHS caused by a bad rotor

That was swapped in this case to no avail.

I had an alternator go bad very slowly on a SMEC car and it caused a similar issue which took the alternator actually dying to rectify. Pun intended. I did get a code 54 with that, but I also had the same thing happen on a 97 Neon which didn't throw the code some years later.

Good thought. That alternator is new as of last summer, so anything is possible. It hits the charging voltage target of 14.2V. How could I test that? I was trying to make a fuel pressure gauge, but I'm unable to replace a fuel pump even if that is the problem, so with the rain, I opted to get inside and try again after work tomorrow if it gets me to work and back.

I just realized that I only looked at the plugs, I didn't see an issue and didn't change them to known good units, so I just went out and did that.

I had an oscilloscope on the alt. I think it was throwing out some unrectified AC current which was freaking out the computer. Unfortunately, I either didn't have it on there when the car would cut out, or I had it testing the sensor signal rather than the power input to them or the computer. It was certainly a learning experience.

what about the wheel in the dist
it it still plasti-melt/riveted nice and snug ?


I had an ignition under accell issue that was hard to find until I noted the lose fit of the coil wire terminal in the coil tower socket
.. long cable flops around , breaks contact

works fine till you stomp the happy pedal and make the cable move..

and ,
last year I had an ABS brake light on in my f150 - most of the year and nothing wrong with the system

last november I replace the alternator - had an intermittent charging lamp then constant

replace the alternator and battery (was borrowed from my car) and low and behold
no ABS lamp since

To test the alternator for issues, just disconnect the field coil wires. It will stop charging and run off the battery.

Good excuse to go through all the engine grounds and check for a loose or corroded wire?

Jeff

A little update from today. It ran poorly on the way to work, but it could maintain the proper speed, so I put little thought toward it. On the way home, it was at it's worst, barely capable of reaching 40 MPH. I pulled off the hyway and into a parking lot and disconnected the white 1 pin bullet connector that is the alternator output to the battery (just behind the battery). Wouldn't you know it, it ran just fine, so I reconnected it and it ran like crap again. Disconnected once more to be sure and it ran well, then reconnected and I arced the connector, leaving a little gob of molten copper in the female end of the connector. I turned off the car, cleaned it out with a screwdriver and left it disconnected for the drive home, or until the battery gauge read low enough to be concerned. That's about 4 off ramps. I reconnected it and MAYBE it's making better connection now due to the better fit of the pin to socket, but it ran perfectly the whole way home.

Further road tests tonight after I spread the terminal out a little more to be sure it's making good contact.

Excellent news!

Just when I thought I was on the right track,..... I'm stumped again.

Yesterday, I changed the alternator with a known good unit and it seemed ok, so I parked it for the night.

Today I made and ran new cables, 4 ga. from the head to the negative battery terminal, and a separate cable , also 4 ga. from the alternator to the positive terminal. I also cleaned the terminals, even though they weren't bad. While behind the battery, I gave all the fuse able links an aggressive tug and broke one of the little orange ones. So I repaired that too. I didn't even get out of the driveway and the stumble returned.

I have a little more info and I don't understand why it does this. On the way to work at 5am, it runs with a slight miss, but I can maintain proper speeds. On the way home at 2pm, rain or shine, it runs terribly. Today, on the way home, it was running very poorly and I was waiting to get to a side street to pull over and try things and suddenly, it was repaired by itself and back to normal.

After the cables today, I made an inline fuel pressure gauge, and I taped it to the windshield, and I'll see tomorrow if that has anything to do with it, but I'm doubtful.

I have checked codes, cam timing, the shudder wheel plastic welds, and watched all sensors through a drb2 and I don't see anything out of whack.

Have you bypassed the baro read solenoid to eliminate that as a possibility? I had one that was bad and causing a cutout due to inaccurate readings once.

I must have forgot to state that I had. yes, I did. Also not mentioned is coolant sensor swap with known good one.

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Originally Posted by shadow88

I must have forgot to state that I had. yes, I did. Also not mentioned is coolant sensor swap with known good one.

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If you are still running the 87 electronics with the MAP in the logic module, rev the car and pull the MAP hose during engine decel to evacuate any moisture from the MAP hose into the car.
These are known and prone to condensation build-up in the line which interferes with the MAP signal. It may take a few times to use the engine vacuum to vacate the line free of moisture.

^ just reminded me of the map replacement in a buddy's charger
- drove like a dog , barely when acting up

sensor was wrecked by the moisture in the line and time

also a problem was the road salt build up in the corner of the lm closest to the rust hole in the wheel well

also , once with my TII set up I had an AIS issue (code)
I replaced it and the code went away but the issue didn't and there was no other codes

so I thought what's the closest thing to the ais"
tps.. so I switched it for another and all was well

swapping back either of the old parts brought the issue back

car HAD to have both but never threw a tps code

It's running the map/ baro on the strut tower.. This morning, drove to work monitoring fuel pressure and that was spot on 55 at 0 vacuum. Rising and falling like it should. Swapped map sensors with known good from my shadow without improvement.

You switched the HEP correct??

Oh yes, known good one again from the shadow, as well as the entire ignition system.

Is it still good with the alternator field coils off??

from experience I know the tps can go without code
from reading I understand so to can the speed sensor

reading the first paragraph of your first post I note it drive differently when you push your foot further down .. using a less traveled portion of the tps sensor (????)

like the gauge dimming in your cluster when old might only work at the brighter settings because the little coil in it is burned up or worn from the contact

Miles, I never actually removed the wires for the field coil, I disconnected the main output wire. I should put it back to stock for diagnostic purposes. Maybe wire in a toggle switch for diagnostics from the inside of the car.

The tps is reading properly on the scanner and doesn't really seem tps related. It's running rough at all times including idle when it acts up.

Oh want is the O2 reading when acting up?
My DD was acting up when I decided to change the O2 just for giggles as the ECU had no codes. A new NGK O2 fixed the issue. Detail are on this site..but I could not find in 5 minutes searching.

When acting up, the o2 cycles as expected on the drb2. I went after the source and went after the field coil part of the alternator. Basically,I removed the fan for access and wired in an interrupter switch to the field coil. BINGO !!! Thats' exactly it. I ran the wires long enough to reach into the car , if needed.

The car acts up, I flip the switch to open the field, and the car runs perfectly (obviously not charging). Flip the switch back and stumbles return.

So.... I'm a SMEC guy. Is the voltage regulator in the LM or PM? OR just wire in an external regulator and call it a day?

it's in the pm
just add a regulator

mine were easy to figure out .. the car died when the battery did

It's pretty easy to switch to an internally regulated alternator too.

I'll be searching for an external regulator today if any stores are open on this Canadian long weekend.

fyi Standard auto wreckers seems to have their u-pick up and running again

drove past last week there was customers parked along the street once again

been a long two years without handy parts seven min away..

Good to know standard has re-opened! I picked up a used PM today and I'll install it tomorrow, but keep the bypass switch just in case. I'll keep this updated over the next couple days.

All,
The common failure in the PM, regarding voltage regulation, is the solder joint at the regulator itself.
It's typically easy to find because the heat discolors the impregnated coating.
Once cleaned, they can be re-soldered and sealed with non-conductive silicone for many more years of use.
Worth noting is the need for air-flow through the PM.
There are many cone filter and other air-flow changes that eliminate air-flow through the PM and that contributes to them being short lived due to heat build up.
Therefore, it's always important to have adequate air-flow through the modules designed around having it.
This includes SMEC and SBEC applications as well.

5digits, I've seen many voltage regulators fail to charge, but this causing a miss fire is new to me. Do you think it's really just a faulty soldier connection?

re power modules
"worth noting"

if you're having serious issues with a power module DON'T leave the battery connected

when there's a power module in the garage that is connected to power .. like a ford cruise control switch , a smoke detector in the garage that's wired into the ones in the house is a good idea

I dropped the hood of my turbo z shut and sat at the desk in front of it
good thing I haven't gone in the house for the night instead
because a few seconds after I sat down
SMOKE STARTED POURING OUT from behind the headlight

so , not a lot of faith in power modules round my place

+ , 2 cars , probably 6 PM's over the 6&4 years I had either
one smec car , never had a bad regulator .. ever in 5 years for that car

Quote:

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Originally Posted by shadow88

5digits, I've seen many voltage regulators fail to charge, but this causing a miss fire is new to me. Do you think it's really just a faulty soldier connection?

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His logic and explanation is solid and an easy thing to check and fix.

Miles, I know 5 digits history in this community. I guess I wasn't clear enough in my question. I want to know if this failure and symptoms are normal, instead of the failure to charge.

Failure of the component itself will caused a failure to charge, assuming it fails in the open position. A Bad solder joint can cause all sorts of bizarre behaviour, If the component has a bad solder joint at a ground point, it could cause a changing voltage as the inside parts reference voltages to ground. This is the same reason that if the car acts weird we always recommend people to check their grounds before going any further. This time we are checking inside the PM.

Not that I'm going to pursue this further, because it doesn't add to the thread, but this charged properly. On the gauge, using a dvom, on the scan tool, it hit the target and kept the battery charged.

New (used) power module took care of this problem for 2 days straight, so I'll call it a well - diagnosed repair. THANK YOU ALL!!!

Quote:

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Originally Posted by shadow88

New (used) power module took care of this problem for 2 days straight, so I'll call it a well - diagnosed repair. THANK YOU ALL!!!

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FANTASTIC news!!!!!

Quote:

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Originally Posted by shadow88

5digits, I've seen many voltage regulators fail to charge, but this causing a miss fire is new to me. Do you think it's really just a faulty soldier connection?

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It can if operating within an undercharged state.