View Full Version : Please held diagnose a 93 Celica - Acceleration Issues

09-13-2013, 03:56 PM
What I'm working with:
1993 Celica STX
Engine = JDM 5AFE - This was swapped in after the original 4AFE died. The swap was done about 4 years ago.
Chassis has 270k+ miles on it. Engine has about 100k on it. When the swap was done I replaced all of the consumable parts and did a good bit preventive maintenance in the engine bay. It's run solid for 4 years.

2 months ago the car died in an intersection. I got a call from my brother asking me to come help him figure out what was going on. I got the car cranked and idled but it had a lot of trouble transitioning from idle to driving. It just chokes and bucks when you start to drive if you don't give it more gas than normal and slowly let off the clutch.
So transitioning from idle to driving is the most alarming issue because if the car doesn't splutter and die it just chokes and bucks in place and the car hardly moves.
The secondary problem is that it behaves this way while driving if you accelerate any faster than an old woman on Sunday after church. Passing is out!! I've been driving his car this week and anytime I feel like passing someone, stepping hard on the gas pedal is returned with shaking/bucking and no speed increase!

So far we've gotten no error codes. The check engine light works and comes on briefly when the key is turned to ACC/ON like it should but I'm not getting any codes.
Because of that I've been focusing on fuel, air, and spark.

What we've tried:

1. Ignition components. I felt sure that it was ignition related so we replaced the spark plugs (gapped correctly), spark plug wires, distributor cap, and the distributor shaft o-ring. After timing the car we didn't notice a difference :(

2. Tested the TPS via the BGB procedure. Checked out. Didn't notice a difference after fiddling with it.

3. Checked the engine bay for damaged / disconnected vacuum lines. I've replaced a few questionable ones, but so far no real good candidates and no progress on this front.

4. Replaced fuel filter. No difference.

5. Replaced fuel pump. I didn't actually do this work. My brother ended up taking his car to a shop because we both got extremely busy for a couple of weeks and couldn't work on the car. They replaced the fuel pump. No difference.

6. Disassembled the air intake all the way to the TB inlet. I just wanted to make sure my brother hadn't sucked up anything that was blocking his intake. Found nothing.

7. Verified fuel pressure. Thinking he may still be dealing with a fuel pressure problem related to the FPR I installed a fuel pressure gauge. This morning I monitored the FP and didn't notice anything alarming. When accelerating the FP rises to ~ 45 psi and when idling it gets down to ~38 psi. That meets BGB requirements so I'm thinking fuel is probably not the issue.

8. Injectors. Via a touch test it seems like all the injectors are firing and the fuel pressure gauge install above verifies that they aren't leaking since FP holds after car shutdown for an hour+

9. New O2 Sensor. This was maintenance we'd been meaning to do for a while now. I didn't expect it to work miracles, but it didn't end up doing much.

Current State:
Still having the bulk of the problems. The above fixes may have smoothed the problem out a little bit but it's still having a lot of the same issues.

Future Tests / Fixes:

1. I want to take another look at the distributor. Specifically to do BGB electrical tests on the coil and see if it is still good.

2. I want to test the MAP sensor via the BGB

3. Check for exhaust clogs or a clogged CAT.

4. Disable EGR

5. ???

More suggestions is what I'm after here. The only thing I've experienced like this is when my Gen3's MAP sensor had a kink its vacuum reference line. I'm pretty sure the MAP is fine on the Celica.

Final Notes:

I don't think its related but his tachometer hovers under 1k at all times. I know the tach gets its feedback directly from the ignitor in the distributor, but I'm thinking the car wouldn't run at all if the ignitor wasn't working. I expect he's just got a few bad caps on the tach's PCB. Still, I wanted to note it.

Any help or guidance would be extremely appreciated!


09-13-2013, 04:07 PM
How's the mechanical timing? Maybe it jumped a tooth or two on the timing belt.

09-13-2013, 04:53 PM
Good suggestion. That's a thought I had as well and definitely one I should move to the front of my troubleshooting list. I just think its something big and simple like that. I'm trying to fight the electrical engineer in myself to go straight to the sensors haha! I've definitely missed obvious things in the past by diving into the harder more obscure troubleshooting.

I'll try and get the top timing belt cover off tonight and see where the camshaft gear is lined up at TDC.


09-14-2013, 01:01 AM
Mechanical timing is where Id recommend also.

09-14-2013, 02:29 AM
Did this problem happen very suddenly or did it run rough for awhile before it finally bit the dust in the intersection?

If it was sudden and immediate I would agree with it jumping a tooth or two. If it was gradual I would look into your EGR/electronics.

Try just pulling vacuum lines and wires randomly and see if anything makes a difference. Also, try pulling your injector plugs one by one and see if pulling one of them makes things better or does nothing at all. They might be firing/not leaking but if they are clogged or spraying a bad pattern they could cause similar problems.

09-15-2013, 11:33 PM
Hey Guys

Sorry for the delayed response but thank you VERY much for taking the time to help me.

Mechanical timing is perfect unfortunately:


That closes one door but eliminates that from being questioned.

I also checked the resistance of each injector and they checked out.

I then moved on to the coil using this test outlined in the bgb:


Primary coil checked out:


Secondary coil did not:


I even checked the resistance from the negative leg just for kicks:


About the same. So I'm getting a resistance of 1659 kOhms when I'm supposed to be between 9 - 15 kOhms. Pretty drastic difference however, I'm wondering if I'm doing anything wrong. I originally did the test on the car but after I got such high values I took the coil out to completely isolate it. Has anyone else measured a coil and gotten funny results? I'm happy to call it bad and buy a new one since its a pretty low dollar part, but I'd love to be a little more sure.

Your advice is appreciated!

09-15-2013, 11:36 PM
Oh yeah. This problem came on very suddenly. Not gradually.


09-16-2013, 12:13 AM
Had a cracked coil on a 5s. Acted like that until it wouldn't start at all. It was a pretty major crack though, someone pressure washed the engine bay while it was hot (no, it wasn't me) :hehe:

09-24-2013, 04:04 PM
Just wanted to follow up and confirm that the new coil fixed the problem. At least, that's what I have concluded since the only feedback from my brother has been that it drives like a new car now

Thank you for all your help.


09-26-2013, 04:29 AM
Glad to hear it got sorted out.