Engine Stumbles When Hitting Rough Bumps - Cause?

4

427Cammer

Registered User
Here is the scoop -- "Check engine" light flashes briefly (1/2 second) and engine quits for 1/2 second, particularly when the RIGHT FRONT wheel hits a rough bump -- typically, the engine flat-out quits for 1/2 second -- DEAD -- RIGHT NOW DEAD -- followed by a very brief check-engine light flash in dashboard -- then engine resumes with a definite miss of one or more cylinders that resolves itself within 2-3 seconds, and engine returns to firing on all six cylinders.

Recently, after above occurred, I brought the car to a stop at a red traffic signal. The idle was stuck at 1500 RPM, and would not return to normal speed. Turned car off, then restarted -- engine idle returned back to normal.

What is causing the engine to briefly cut-out, every time I hit a moderately severe bump -- problem is worse when suspension is set to "FIRM".

A possibility? -- have some kind of go-fast computer chip attached to factory computer -- possibly the contacts are dirty or corroded, and/or the EEC is loose on its kick-panel mount, and is bouncing around?

Is this an early symptom of a pending harmonic balancer failure?

Are old motor mounts allowing the engine to sit too low in the chassis, so that every time car bounces hard, motor pinches something? When experiencing this momentary dead-motor issue, I have not noticed any blip or flicker in any of the dash or headlights, suggesting that the issue is not likely some sort of a intermittent dead short.

Brief history -- car is factory stock (except for 3rd party EEC chip) 1990 SC 5-speed, that has been in storage since late 1997, due to blown head gasket. At the time of storage, EVERTHING else worked perfectly -- all electrics, alarm, and other mechanicals. Recently replaced motor with a good running stock donor 1990 SC motor -- am trying to iron out YEARS of storage-accumulated bugs and hiccups in the electrics and mechanicals.

Thanks for the assistance.

Cammer
 
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If you're getting a CEL, then pull codes. It sounds like a loose connection somewhere: cam sensor, crank sensor, bad ground, dis, etc.

Mike
 
Couple of thoughts...

I would definitely check the engine mounts. If they are the stock "jelly donut" type then they have probably collapsed. This can cause all sorts of idle/stalling issues (related to the knock sensor, I believe). Another thing to check is the main ground strap from the battery to the driver's side engine mount. When you hit a bump, does the car lose all electrical power? If so, you have a bad ground connection, which could be related to a failed engine mount...
 
OK, guys -- here is the question -- how does one "pull the codes?" I understand that these EEC codes will each represent a potential fault area to check -- but how does one access them without some sort of a car computer evaluation device?

Sorry -- newbie to wrenching on the SC -- my collection of machines are from the 1960's and early 1970's -- nothing electronic or computer controlled about them.

Thanks again. Will check the motor mounts -- what should I be looking for, other than obvious indications that mount(s) are collapsed, and motor is sitting on the pan against the crossmember?

LJGriggs -- does not appear to be an electrical fault, as none of the lights in dash or headlights blip when motor briefly goes dead.

Cammer
 
You should find an adapter interface under the hood called EEC Test or something like that. There's some pointers on how to use a paper clip to trigger the test modes on it, but the tricky part is getting back into the car and start counting the number of flashes the CE light does...... but the easier way is to buy a scan tool that plugs right in and gives you the numbers. I bought one for about $40 CDN up here and its great :).

The other method if you can is to drive the car to autozone I think it is, and I heard they will hook up a scanner for you and give you the codes.
 
Thanks for the responses -- I am not an *official* member of the SCCoA yet (dues have been sent, just not cached in, yet) so I only have access to the non-member areas -- will look around the board for more info on how to read the EEC codes.

Anyone have a recommendation for a scan tool type or brand? Anything that I should stay away from?

Appreciate your replies, as always -- am slowly getting my SC back in shape with your help.

Cammer
 
All of the suggestions are of value to check out, but because the problem occurs when you hit bumps I suspect something not mentioned yet. There is a wire harness that connects the DIS module with the crankshaft sensor and cam sensor. This harness, if not secured properly can make contact with the blower belt and may wear a bare spot in the harness. This may cause the wires to contact each other and short out temporarily when hitting a bump.
The symtoms are similiar to a failing DIS module, and if the bare wires aren't found I would check out the DIS module. John
 
How to read blinking cel

you really don't need the tool to read the cel lights. Here is my cheat sheet. just print it out and follow the blinking lights. It is so easy you won't bother with a reader. You can get a list of codes from a manual or various other places on the web.

sean



Key On Engine Off

Find STI
Connect terminal to good ground.

Turn Ignition to on
Check engine light turns off
Fuel pump runs briefly
Cooling fan(s) run briefly
All other actuators will be switched on / off

On Demand Codes displayed
Can be two or three digit codes
Displayed as flash sequences
4 second pause between codes

This is repeated once if there is more than one fault.

Pause 5 – 7 seconds

Flash once

Continuous Memory codes follow
Can be two or three digit codes
Displayed as flash sequences
4 second pause between codes

Delete Continuous memory
Remove ground while fault codes are flashing

Key On Engine Running

Find STI
Connect terminal to good ground.
Start Engine
After a few seconds engine speed will increase
Check engine light will flash
Number of flashes will indicate cylinders (3 for v6)

Apply and release brake pedal
Turn steering wheel one half turn

After additional tests the check engine light will flash once.
Snap the throttle

Fault codes will be displayed

If no fault codes are present pass code will flash 11 or 111.
 
IGNITION SWITCH.

I had the exact same symptoms when my switch was coming apart. Its in the steering column under the two piece cover. 10 bucks at the part store if its coming apart like mine was. :)
 
Latest incident -- was driving car at 40 mph, 3rd gear, and hit a very sharp road section that caused the whole car to jump -- this killed the motor, and the motor did NOT recover, as it usually would (see first post in this thread).

Coasted into a nearby parking lot, motor would NOT restart. Cranked just fine, but it appeared that there was no ignition (just a WAG gut-instinct) -- there seemed to be NO noticable electrical shorts -- all of the lights and guages worked normally. Could hear the electric fuel pump running when the ignition was on. Left car in lot all day, while attending to other business. Returned that evening, and started the car. Car started quickly, but would not fast-idle, and I had to feather the gas for 5-10 seconds to keep it running -- was a bit rough as it idled, but not too much so -- finally after 10 seconds or so, car idled normally, and smooth.

It SEEMS that the sharp road jolt is somehow killing power to the computer system, causing it to temporarily fail. Upon restart, computer has to re-orient itself.

The car only dies when I hit a sharp road bump or pothole at road speed -- no problem going slowly over parking lot speed bumps.

Pulled the computer codes -- got an 82 (electric fan seems to work fine, so likely a supercharger bypass valve problem) and a 33 (EGR valve not opening or not seating) -- no other computer codes were noted. IF the computer system is losing power, then there would be no code to reflect the temporary power loss to the computer.

Pulled the DIS plugs, the cam sensor plug, and several other underhood plugs and sprayed them down with CRC contact cleaner.

Checked to see if the positive battery terminal was touching the hood -- has factory rubberized cover over the cable end, that envelops the entire positive cable end -- directly above the positive battery post, on the hood, is sound deading material -- no bare metal on hood. Battery is not tied down with factory hold down, rather simply sits in the tray snugly.

Checked DIS harness around supercharger snout area -- looks fine -- no insulation rubbed through.

Pulled apart steering column, and double-checked that the wiring was not melted, and ignition switch is intact -- visually checked, and everything looks OK.

There is one fuse in the fuse block under the dash, that simply says "Run." I presume that this is the main fuse for the motor electrical and/or computer?

Since the car has been sitting for 9 years in a garage, it is possible that some connector that supplies power to the ignition and/or computer is corroded or otherwise making a poor connection. Am thinking that I will pull the battery cable, then pull the main underhood fuse block fuses out, one by one, and spray down and reseat and the same for the fuses under the dash. Also, I will pull the main connector on the computer, spray with contact cleaner, and reseat.

Any new thoughts, based upon this latest incident?

Thanks ahead of time.

Cammer
 
Dying Engine Problem Resolved

Update -- replaced the ignition switch, which sits on top of steering column, and the engine dying problem appears to have been resolved. Have pounded over MANY rough sections of road since changing two weeks ago, putting over 1200 miles on car.

While I was at it, replaced the cam position sensor also -- 5-minute job with a 7/32-inch socket -- simply a preventative, since original one was still in car. Am presuming that replacing the cam position sensor did not have anything to do with curing the engine dying problem.

FWIW -- when removing the ignition switch from the steering column, you will need a tamper-proof torx bit to remove the two screws holding the switch to the column -- I bought mine at Sears, as part of a set of tamper-proof bits -- $25.00.

Ignition switch cost - $12.00
Cam position sensor cost - $39.00

Thanks for all of your suggestions and advice. You guys are GOOD !


Cammer
 
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