[Shotimes] Sick SHO (long)

[Jonas Diener]

Hi guys,

I'm new to SHOtimes, having just bought a SHO on Monday.  Sorry for the long post, but I wanted to give the complete picture.

It's a red '92 MTX with a myriad of problems, but the price was right.

Right now I'm trying to figure out why the engine is feeling sick.

The sickness manifests itself in several different ways.

The first I noticed is that sometimes it is real hard to start, and will only eventually start firing after cranking for 30-60 seconds and giving it lots of gas.  Other times it will fire right up.

Trying to diagnose it I pulled one of the plug wires and stuck a metal tool into it, and could see a spark leap from the tool to the intake as I cranked it, so I know it's making a spark.

I pressed a tool into the check valve on the fuel rail and fuel sprayed out, so it has fuel pressure.

I even pulled one of the plugs out and stuck a paper towel in the plug well.  It got fuel sprayed onto it when I cranked, so the injectors are firing.

The second manifestation (or maybe a different problem) is a stumbling problem when I step into the gas too much (anywhere past 1/4 throttle).  It's especially bad at low RPMs.  It runs smooth if I stay light on the gas, but when I step on it more it stumbles and then feels like it's not firing on all cylinders.

It seems to be worse in colder weather.

My first thought was of a clogged fuel filter, so I changed that and it didn't make much of a difference if any.  I checked the air filter too and blew it out with compressed air.  It was somewhat dirty but not bad.

Unfortunately the fuel pressure gauge I have has a larger thread size than the check valve, so I can't check the fuel pressure.  Anyone know where I might find an adapter?  (The gauge fits perfectly on my '87 5.0).

These two symptoms together sound exactly like a bad CID sensor as described here...

http://www.shoshop.com/guidelog/v6/p021.htm

...with one exception.  They say that a continuous failure code will be stored in the EEC memory if the CID goes bad.  When I check the continuous codes I don't get a CID-related code.

Running the test sequence, the KOEO test reports 111 (everything OK), and I get one continuous code: 542 Fuel pump secondary circuit failure.  Anyone know what this means?  After clearing the continuous codes and driving home the 542 didn't show up again.

When I run the KOER test, the engine always stalls about 3 seconds before giving me the goose flash.  I went ahead and hit the brakes and WOT even though the engine was stalled, and got these codes:

129 Insufficient mass air flow (MAF) change during dynamic response test.
225 Knock sensor (KS) not sensed during dynamic response test.
521 PSPS circuit did not change states.

I understand I got the 521 because I didn't turn the steering wheel during the goose procedure (hard to do without the engine running).  Could the other two codes be legitimate, or did I just get them because the engine stalled during the test due to some other problem?

Other symptoms include a not-so-smooth idle and a pop-pop sound sometimes when I let off the gas at high RPMs.  Also the tach doesn't work (bad sensor, possibly related?)

Next I plan to pull off the Y-pipe and check the condition of the cats.  Perhaps they are messed up and constricting the exhaust flow.

I suppose I could have a bad MAF sensor, bad HEGO sensor(s), or maybe a TPS (it does seem related to certain throttle positions).  I don't really want to spend money replacing them if I'm not sure they are bad.

I also noticed that the front plug wells were quite full of oil (indicating a need for new plug well seals).  I cleaned them out, but I imagine the rears are in the same state.  Could this be causing my problem?  Doesn't make sense to me since it's fine at part-throttle, but it's another variable.

Whew, that was a long message.  Anyway, if y'all have any hints, advice, or insights, I'd love to hear 'em.

Peace.
-- 

the truth may be out there
but lies are in your head