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'85 3.8L quits under a/t load

 
nealyates
New User
Posts: 3
Joined: 06/13
Posted: 06/07/13 06:23 PM

I have owned this car, an LX ragtop, for eight years without a single problem. It had complete rebuild/restoration about 10 years ago at 95k. Now has 136k of summer use. Engine starts and runs fine, but I took it out of winter storage, and since then whenever I had to brake to a quick stop, it felt like revs would drop through the idle and die. If I let up on the power brake a bit, it would be fine. Never actually stopped running on me. Then last week, on an out-of-state trip  I put it into Reverse while backing into a parking spot with power steering turned full and it suddenly quit. Twice. I left the space an hour later with no problem only to have it quit when I slid it into gear pulling out of a side street.

After 20-30 tries (start-shift-die) sitting in the middle of a main road, it suddenly kept running and I was able to get it onto a side street. I let everything cool down for a few hours, and tried again. Same thing. start, shift into D or R and it died, not sputtering as if starved for fuel, but instantly, as if someone threw a switch.

Flatbedded 50 miles to home, I installed a new IAC and, for good measure, a new PCV and air cleaning element. No help. Looking back, it seems to quit whenever under some sort of load (ps, pb, or tranny engaged). Any thoughts?

Thanks  

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waynep712222
User
Posts: 124
Joined: 03/13
Posted: 06/07/13 09:19 PM

ok... first.. this is a 1985 with a CFI 3.8.. Central fuel injection.. green topped fuel injectors on top of a throttle body...

first is to examine the wires for insulation that fell off..  it has happened before.

second... lets look for vacuum leaks.. there is a vacuum tree on the firewall behind the motor.. where a big hose hooks up then everything branches off of that..  are all the caps and hoses still tightly attached..

now.. lets test the power brake booster...

warm the engine up... so its easy to start..

shut the engine off.. pump the brake pedal 5 or 6 times... and hold your foot on the brake pedal with about 70 or 80 pounds of pressure on the brake pedal.. while holding your foot steady on the pedal..  start the engine..   does the pedal drop???? slightly.. it should..

now.. shut the engine off...  with steady pressure on the pedal. it should NOT RISE if it does. then the brake booster or the check valve is bad..

leaking brake booster will cause idle issues.. as its like a huge vacuum leak...


there is a possibility that the transmission could be causing this.. block the front wheels after you have jacked up the rear wheels... place the transmission in neutral..   start the engine...

without touching the brake..   and the wheels are free to spin.. pull the gear shifter from neutral to drive..   now that the rear wheels are spinning.. apply the parking brake. not the service brake.. does the engine stall??

you should only need to step on the brake to pull it out of park.. it should start in neutral..

please make sure the wheels are completely stopped before you shift into any other gear or neutral..   or turn the key off and allow them to come to a stop..

i hate the noise of the parking prawl lever ratcheting on the parking prawl...   tatatattatatatatattatatat..


there are other things to check also...

the thermactor system.. AIR INJECTION system..   inspect the check valves that feed either into the back of the exhaust manifolds.. or into the back of the cylinder heads..

then figure out which of the hoses into the upstream air injection manifold..  carefully disconnect the hose that go into the check valves..  plug the check valve side so no air can be pulled in.. plug one side of the hoses if it comes out as a pair..

have somebody start the engine.. while you feel any air coming from the end of the hose.. it should have air for the first 8 or 10 seconds of start up..  then if the motor is up to temp.. the air from the diverter valve into the UPSTREAM air should shut off..

any UNCOMMANDED air into the upstream exhaust manifolds when the system is in closed loop when its calculating fuel control from the oxygen sensor readings..  this throws it out the window and causes all kind of problems..  

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waynep712222
User
Posts: 124
Joined: 03/13
Posted: 06/07/13 09:26 PM

you will want if the above power brake booster checks out good... and pulls down when the engine starts.. but does not let up when you shut off the engine..  if it lets up. the booster or check valve is bad.


do you have one of the actron EEC IV code testers.. so you can run the KOEO and then the KOER test..  they are about 32 bucks at most parts stores...   please post codes..

have you ever run a KOEO and KOER test before???

Key On Engine OFF...

key ON. Engine Running..  

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nealyates
New User
Posts: 3
Joined: 06/13
Posted: 06/08/13 04:53 AM

Thanks for such a detailed, plain-language and rapid response. Am heading out to my garage and will follow your list. Will advise!  

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nealyates
New User
Posts: 3
Joined: 06/13
Posted: 06/09/13 06:03 AM

- checked insulation, nothing missing.

- checked for vacuum leaks, nothing apparent, but I know they can be hard to find.

- checked brake booster; it's operating properly. Only starts in Park and Neutral as it should.

- jacked up rear wheels and did the test w/parking brake. Engine stalled instantly.

Other than previously replacing the Air Idle Control motor and PCV, did not do anything with the Air Injection system as yet: got side-tracked and ran out of time. Havew to be gone today, as well. On Turesday, I am replacing the distributor cap, rotor and wires and plugs. Have also bought a new inline fuel filter, but not yet installed. Should I also change the O2 Sensor?

Much thanks to all for the advice!  

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