1994 2.3L Engine runs better with diagnostic test jumper installed - why?

[jstelmack]

From previous thread: 1994 2.3L 5 speed base model Mazda B2300. Engine ran ROUGH, no power, backfired, bogged down etc.

Replaced Fuel pump assy, cleaned tank, new fuel filter. Cleared codes. Added SeaFoam cleaner to tank of fresh gas.

codes 111,111 and that's all. Looks like only "pass" codes under KOEO or KOER tests.

Driving around I can tell it is getting progressively better/more power/no back fires/less bogging down. Suspect the SeaFoam is slowly cleaning out the injectors.

THE PROBLEM - I noticed that, by error, I left the jumper installed on the diagnostic connector. Engine running when I remove the jumper. The engine immediately dropped in RPM and started running noticeably rougher. I did a few drive tests, with jumper installed and jumper removed. When jumper installed the engine performs much better, although still lacking typical power. With jumper removed, the engine bogs down under throttle and has less power. But it does not backfire anymore.

Any ideas what could cause this? Several KOEO and KOER tests have been performed since replacing the fuel pump and clearing codes. Consistently get 111, 111 PASS PASS.

Thanks!

 

[jstelmack]

Additional findings:

When attaching the negative battery cable there are sparks indicating a current drain. Key is off and all accessory switches are off. This happens with the test jumper installed and it happens when removed. I'll track down which circuit is misbehaving. note: I saw this same issue in another thread but there was no solution given.

UPDATE: 12-19-2011 - Doing the light test between positive battery cable and pos battery terminal, there is only a very brief pulse of current when hooking it up. The light flashes very quickly and then goes out. I believe there is no issue with key off current.


Starting to think the original idea of replacing the engine with a distributor non-computer driven engine was the right solution to begin with.

 

[jstelmack]

No suggestions? Where did all the experts go?

 

[MrShorty]

The main thing I can think of that changes when the diagnostic connector is connected is that the computer fixes timing advance at base + 20. Perhaps something is off in the timing computation causing it to have issues.

I'm not familiar with the 2.3. Distributor or Distributorless? Knock sensor present? EGR system?

 

[Tbars4]

No suggestions? Where did all the experts go?

..Other thread can be found here..
http://www.explorerforum.com/forums/showthread.php?t=337762

...Starting multiple threads on one's vehicle problem makes it difficult for those who were following along to not only help diagnose your problem (as you may only be sharing some of the information in one thread while not in the other), but now you need to find and follow multiple threads for one end result..

 

[jstelmack]

Good point on different threads. I figured the fuel problem was resolved and on to other problems... Bad move on my part, agreed. I agree with your assessment on the timing issue. It "sounds" to me like the timing is advanced or "late spark".

SOME DETAILS:

2.3 L EEC IV.
Distributorless
EGR Yes
Knock sensor - don't think so.

two coil packs, one for exhaust side plugs, one for intake side plugs. Plug wiring correct.

Camshaft positioning sensor exists, but is not used on this model. IS NOT a California model. The part that spins around with the window vane opening is 50% open - 50% closed. Removing the camshaft position sensor electrical connector has no effect on engine performance, but the PCM throws a code reflecting the "bad" sensor. Inspection of the inside of the camshaft position sensor reveals it looks new. No cracks, breaks, abrasions etc.

Engine running - Alternator charges above 14 volts. Engine off battery shows 12.4 volts.

I'm told AutoZone will test the coil packs and PCM for free. Will try that. First, I'll try disconnecting the exhaust side coil pack. It's my understanding that this provides spark on the exhaust stroke to fully burn unspent fuel/air and lower emissions... Freakin EPA!