‘93 comes alive, but runs trashy

[Zpak]

Quick backstory, received ‘93 MTX non running, knew it wasn’t getting fuel, suspected fuel pump.


Got SHO1 shoved into the garage and confirmed no fuel at the rail, heard (what I thought) was the pump screaming at key turn to prime, and the inertia switch was good. Already had a pump on the bench so got after it. Car is astoundingly clean underneath, zero rust. Amazing and unheard of in northwest Indiana. I can get use to working on Cali cars. Little tight with subframe connectors but got it out with very few arguments. When I say clean I mean clean. Found the tank build sheet still attached to the top of the tank.

Pulled the sending unit and tested the resistance, it checked out good so I swapped the pump out and slapped it back in. Fished the tank back up and good to go. Turn the key, the same scream. No way! I’m thinking well that’s impossible. Start searching around and found what I had always assumed was the pump wasn’t. Pinpointed it to the back passenger door. Said ok, I’ll dig into that later let’s fire this up.

Prime, prime, crank, nothing at the rail. Try again… nothing. “Why didn’t I test the pump wires???” Ok hold on I never checked fuses because I thought the noise was the pump. Boom, lousy 10 amp ACCY FEED/ALIM ACESS" Fuse was blown. Ok we’re on to something. New fuse, crank sputter. Shot of ether, fired up! First time I’ve heard it run. Couple hiccups but smoothed out and was idling great. Couple cracks and it had a pretty good hesitation. I knew that was probably a bad sign. Warmed up though seemed good enough for a once around so sent her out. Ran like absolute trash. Cutting in and out, low power, sputter, bogging… limped it back. Had about enough SHO time for the day but wanted to check for codes.

Pulled a 564 and had stored 212, 542 and 217. For now, I cleared them and hung it up for the day. I’d like to do a run test but haven’t figured out exactly how yet. I’m using a Sunpro scan tool. Man it’s been a long time since I’ve messed with OBD 1.

So, from this point I welcome any advice in what to further test/check or a direction to help get this thing figured out.

Oh, and the screaming noise… I took the door panel off and kept listening while my dad turned the key. Pinned it down to the stupid door lock motor. Why the car locks the doors when you hit the key I have no idea but that’s the culprit. It’s bound up and not working anyway so for now I just unplugged it. Ahhh quiet.

 

[ScotSHO]

Easy things to check
- Spark plug wire order incorrect?
- Does the tach move & look good during startup? (Cam sensor is good then)
- Do you have a large vacuum leak?

Harder things to check
- MAF bad? Need a known good one to swap out.
- Has the timing jumped? Do a front 60k. Get a new crank sensor just in case (probably not the issue).

 

[Zpak]

Easy things to check
- Spark plug wire order incorrect?
- Does the tach move & look good during startup? (Cam sensor is good then)
- Do you have a large vacuum leak?

Harder things to check
- MAF bad? Need a known good one to swap out.
- Has the timing jumped? Do a front 60k. Get a new crank sensor just in case (probably not the issue).

Appreciate the response. Ok key on the tach bumps up to like 100 but just hangs out there after start up. Give it a rev and it jerks up in 3-400 rpm chunks and falls the same. One shut down it never came back to zero and stayed at 1000. It does start up every time though. So no the tach is not smooth. Wires are correct on the coil.

I did notice a missing line on the bottom of the throttle body. Looked at the running parts car and it was the same. Any idea where this is supposed to go?


From what I’m told, and receipts show, this engine was just rebuilt a few hundred miles ago. It was good right after then basically a couple hundred miles later started running how it is now. It has an 80mm MAF and I believe a tune chip which I’d assume accounts for that so swapping a stock one in would probably come with its own issues.

 

[Zpak]

Would unplugging the cam sensor and seeing how it runs without it rule out the cam sensor?

 

[luigisho]

You have an EVTM manual for mtx car? electrical might vary a bit but vacuum and coolant hoses would be the same

I haven't pulled that stuff apart. THere are vacuum ones and one for coolant to help with cold weather icing or something

 

[Zpak]

You have an EVTM manual for mtx car? electrical might vary a bit but vacuum and coolant hoses would be the same

I haven't pulled that stuff apart. THere are vacuum ones and one for coolant to help with cold weather icing or something

I do not

 

[luigisho]

Have you verified it has a chip in the pcm? I would do that. If you have a 55mm oem one you could switch it back to stock easily. Removing the tuning chip and a battery disconnect for a good reset will default to stock tuning.

 

[Zpak]

Have you verified it has a chip in the pcm? I would do that. If you have a 55mm oem one you could switch it back to stock easily. Removing the tuning chip and a battery disconnect for a good reset will default to stock tuning.

I’ve read it’s easy to spot but have zero experience. It’s plugged in the PCM between factory plug? And, all behind the glove box?

 

[Zpak]

I’m going now to do a KOER test and see what it says.

 

[zoomlater]

for code 212:

Is there a text for the ignition control module

My son's 94 3.0 recently started misfiring when under load. The idle is also somewhat erratic at times. Pulled the codes and got 212 and 219. Is there a test procedure to rule out a bad ignition control module?

shoforum.com

for code 217:

Nasty Electrical Grimlin

I'm pretty baffled and have tried to search around the forums for this problem, but I could have missed something. Now for some basic information, I have a 95 MTX that ran well up until this issue occurred. When I was on my home, pulled into my neighborhood, then all of a sudden its running...

shoforum.com

 

[zoomlater]

Would unplugging the cam sensor and seeing how it runs without it rule out the cam sensor?

that is the easy way to see if its the cam sensor, it might take a few tries to start as the computer is guessing when to fire. if it runs fine after that, then its the cam sensor, or at least for that issue.

 

[zoomlater]

Appreciate the response. Ok key on the tach bumps up to like 100 but just hangs out there after start up. Give it a rev and it jerks up in 3-400 rpm chunks and falls the same. One shut down it never came back to zero and stayed at 1000. It does start up every time though. So no the tach is not smooth. Wires are correct on the coil.

I did notice a missing line on the bottom of the throttle body. Looked at the running parts car and it was the same. Any idea where this is supposed to go?
View attachment 95965

From what I’m told, and receipts show, this engine was just rebuilt a few hundred miles ago. It was good right after then basically a couple hundred miles later started running how it is now. It has an 80mm MAF and I believe a tune chip which I’d assume accounts for that so swapping a stock one in would probably come with its own issues.

a small coolant hose connects to that port, there are pictures of it on a members link. let me find it

Collection of SHO Repair Information and Photos

For the newcomers here, Over the years, I've built up a good sized collection of SHO Gen 1 and 2 repair information, including things like printouts from the old SHOPhoenix web site, the SHO Engine Book, and much more. I've also collected many photos, some downloaded and lots from my own...

shoforum.com

 

[Zpak]

a small coolant hose connects to that port, there are pictures of it on a members link. let me find it

Collection of SHO Repair Information and Photos

For the newcomers here, Over the years, I've built up a good sized collection of SHO Gen 1 and 2 repair information, including things like printouts from the old SHOPhoenix web site, the SHO Engine Book, and much more. I've also collected many photos, some downloaded and lots from my own...

shoforum.com

Thanks a lot man, appreciate it.

 

[zoomlater]

Throttle Body coolant bypass mod instructions??

Finishing up a full 60k and I want to do the coolant bypass mod but the 3 hoses has me confused..... I'm thinking loop the large coolant line that feeds the TB with the IAC adaptor coolant output that goes to the thermostat housing and just plug the other one??? If anyone has a schematic,I'd...

shoforum.com

here is a discussion of what that hose is

 

[Zpak]

KOER test came up with:
226 Ignition Diagnostic Monitor signal fault
116 Engine Coolant Temp sensor

KOEO after clearing everything yesterday and all the running today gave 111 so nothing and I guess re-stored 217 and 542.

 

[Zpak]

Throttle Body coolant bypass mod instructions??

Finishing up a full 60k and I want to do the coolant bypass mod but the 3 hoses has me confused..... I'm thinking loop the large coolant line that feeds the TB with the IAC adaptor coolant output that goes to the thermostat housing and just plug the other one??? If anyone has a schematic,I'd...

shoforum.com

here is a discussion of what that hose is

Well that explains it. Guess that’s a reasonable mod for a desert car.

 

[ScotSHO]

Appreciate the response. Ok key on the tach bumps up to like 100 but just hangs out there after start up. Give it a rev and it jerks up in 3-400 rpm chunks and falls the same. One shut down it never came back to zero and stayed at 1000. It does start up every time though. So no the tach is not smooth. Wires are correct on the coil.

I did notice a missing line on the bottom of the throttle body. Looked at the running parts car and it was the same. Any idea where this is supposed to go?
View attachment 95965

From what I’m told, and receipts show, this engine was just rebuilt a few hundred miles ago. It was good right after then basically a couple hundred miles later started running how it is now. It has an 80mm MAF and I believe a tune chip which I’d assume accounts for that so swapping a stock one in would probably come with its own issues.

That is a coolant line for the throttle body (to warm it up in the colder months and improve drivability). Many people delete those 2 connections (the in and out of the throttle body). Yours might be deleted and capped down near the thermostat.

 

[luigisho]

YOu empty the glove box, press in the sides of the glove box so it will come out of the track and let it hang down. You will see the back of the pcm. There is a port on the back that is easy to spot especially if anything is sticking out of it.

 

[Zpak]

Ok just got a valuable piece of information from the previous owner. I knew he took it back three times post rebuild because it started running bad shortly after it was returned. What I never knew is every time they “fixed” it, the car did run good again but only for a short time.

Here was the diagnosis, and what they changed, three times:

“After the coil pack was installed, the low RPM at idle, choppy running (some misfiring) hesitant and jumpy acceleration, erratic tach, etc. continued.

On 7-26-18 a diagnosis stated:
The technician found no spark in 2 cylinders, technician lab scoped the ignition module and found no output to the ignition coil. Technician also found spark plug wires are shorting out to the intake manifold causing premature failure to the ignition module.They replaced the plugs, plug wires, and ignition module. Ran fine for 50-70 miles, then the same exact scenario played out again.

Did diagnosis again on Jan 21 ‘19 with same results AFTER new parts I mentioned were replaced; they said “your faulty ignition cables caused the ignition module to go bad AGAIN.
They replaced the same parts again; new plugs again, new plug wires again, new ignition module again.
Car ran fine for 60 or so miles and once again, the same thing.

The final repairs (same as b4 3 times) was in Feb 9 ‘21. Mileage and was 125003. Got it back and at 125069, same symptoms were beginning to start again and I said, f it, that’s it, and she’s been in my garage ever since.”

So that being said, that leads me to believe my hunch that it’s been the PCM this whole time. Bad cam position sensor aligns with erratic tach, but it starts no problem every time, car idles smooth as silk without skipping a beat, but give it gas and it falls on its face.

Thoughts, opinions, ideas, am I on the right path?

Oh, and by ignition module, I’m assuming they’re referring to the DIS?

 

[Zpak]

Ah, one more thing. It was given to me in the mod list and I had to look it up because I had no idea what it was. The
Ted Breaux LPM. Obviously been around for a while now. Any track record of them failing or corrupting?

I will start with lugisho’s suggestion to remove that and see what happens returned to stock. But, just curious if there has been any reports over the years of the chips failing or otherwise causing problems.

I searched around the forum a bit but the newest discussion mentioning the chip was like 2009 so…