Mike M

I've been through the wringer.......
I restored a non molested 1989 Formula 350 TPI for my Brother a couple years ago. Recently he brought it to me with a new problem.
It has an intermittent stutter and is running rich.
Also the TCC does not engage but the cruise works fine.
Transmission shifts properly. TV cable is set properly. Trans filter and fluid replaced.
There is no check engine light. It does not suffer from a lack of power. At WOT is runs like a bat from Hell. Here is a list of what I have replaced just to be sure.
New Distributor with all new components.
New plugs (AC delco gapped correctly)
Wires. There was no arc. with the old wires, just wanted to be sure by replacing them.
New Ignition coil.
I swapped the ECM with PROM from my own 1988 350 TPI GTA. The result was the same stutter on the Formula.
I added an additional ground cable from the Ignition coil mount to the firewall. The OEM braided ground strap is in excellent condition along with the battery to chassis ground as well as the battery to engine ground.
PCV is not clogged. There is no vacuum leak on either hose.
The voltage at the ECM battery terminals as well as the grounds are good.
The alternator is charging correctly and the battery is new.
All sensors have been tested and check out good i.g. MAF,TPS,IAC,CTS,IMT, etc.
TPS, IAC and base timing have all been re calibrated. There was no change when the EST was disconnected.
There is no change when the vehicle warms up. Cold or hot makes no difference.
Fuel pressure holds steady @ 41 PSI after key is off. I followed the troubleshooting chart and determined the injector o-rings are good.
FPR diaphragm and spring replaced, checked .
Vacuum tested after check valve and holds steady. All vacuum lines are good and not collapsing under vacuum (not soft).
Injectors replaced with Bosch type 2 and all ohm out within tolerance when cold and heat saturated.
Voltage @ injectors checked and is good.
Harness on top of engine checked and is good.
I decided to remove the plenum and runners to check the EGR and it's function. Here is what I have discovered. The EGR solenoid was opening and closing vacuum however it looked very rough. The casing had degraded and the coil windings were turning green. I decided to replace it with the 1994 Caddy upgrade I read about in similar threads. The EGR itself is intact. It holds vacuum and after removing and inspecting it is clear of any carbon deposits. The EGR temp switch had continuity at room temperature. If I'm not mistaken it is a normally open circuit. I have ordered a replacement. I will also be replacing ALL hard and soft vacuum lines as well as nipples. I did discover a crack in the hard line from the plenum to the FPR. After reading the shop manual in depth I discovered the EGR function was not being asked for from the ECM as my Park / Neutral switch was misaligned. I have corrected that as well. The car did not start in neutral which is why I suspected a problem. I am replacing the injector o-rings and plenum / runner gaskets upon reassembly. I am currently waiting for the EGR temp switch to arrive. A new o2 sensor is in the works also.

Compression test reveals all cylinders and valves healthy. The car will definitely get out of it's own way.
I also noticed a discrepancy in the vacuum diagram for 1989. The plenum does NOT have a vacuum tap in the front directly under the throttle body. I have modified the diagram to depict the routing I will take upon reassembly. I assume the EGR does not need a constant vacuum supply therefore it does not need a connection after the check valve but before it.
Please see the diagram and photos for the detail.
This is where I stand so far. I would appreciate comments from senior members with experience.
I will be updating this thread once I have it reassembled.
Mike M

aliceempire

iTrader: (14)

To start, how do you know it's running rich? What did the old plugs look like? What do the new ones look like with a little run time? What size are those injectors?


Second, the vacuum line that feeds vacuum to the egr solenoid goes to the TB itself, not the plenum. The undrilled and untapped part of the plenum you circled is supposed to be that way. The port you want is in the bottom of the TB, I've never seen one without this. That's ported vacuum that only has vacuum when the TB blades are opened.


Everything else you checked seems fine unless you tested something wrong that we don't know about. In which case, it's really hard to go over all of your homework.


Other things you could look into is engine health..... compression, valve adjustment, timing chain super stretched.

Mike M

I can smell the exhaust running rich. It burns my eyes. It is a smell that is hard to mistake.

The old plugs were burning clean but had a slight odor of fuel on them. They were burning clean as I had an Accel ignition module and MSD coil. I have replaced all components as possible causes for the problem along with new wires, plugs, coil, distributor.

The plenum and throttle body are the O.E. components for this car. Evidently GM made a design change. This thread exists so that someone might shed some light on this change. I am definitely not drilling and tapping that port.

Compression test reveals all cylinders and valves healthy. The car will definitely get out of it's own way.

aliceempire

iTrader: (14)

Then I'm not sure what you're asking. The drilled part you have circled on the plenum was never used for any vacuum port on any tpi equipped vehicle as far as I know. There is a similar one at the rear too, which leads me to guess the holes were for alignment to make sure other holes were drilled and tapped in the proper place. Could very well be for another reason but I'm doubting it was ever intended on being a vacuum port. History officianados may know on the History board. I've worked with TPI of all years including 89's and of them did not have that drilled.

On the other hand the port in the bottom of the TB I've seen on every tpi TB I've ever seen and that will be the one you need. Is it not in your TB? I wouldn't hook up the egr any other way. Every factory thirdgen tpi vacuum diagram shows them using this port.

I can't wait till you get this back together, I hope all your work pans out to success. I can't think of a good reason it won't.

RedLeader289

iTrader: (2)

Didn't read your whole post (apologies all around), but did you replace the ICM? (Ignition Control Module)? Because from my own experience - these cars eat them like candy, they can cause a myriad of problems that in no way seem related to the ICM but magically go away upon replacement, and they're cheap and simple to replace.

aliceempire

iTrader: (14)

I took a guess he change it when he replaced the distributor.

RedLeader289

iTrader: (2)

I thought that too, but I've seen (personally) them go bad within a couple weeks so I thought I'd throw it out there. New parts can be 'duds'.

aliceempire

iTrader: (14)

No doubt. That's why I hate troubleshooting by throwing parts at it.

Mike M

You are exactly right. I am an imbecile. I did not look closely enough at the throttle body before jumping to conclusions. I guess I was focusing so hard on everything else.

Mike M

When the Accel ICM died I replaced it with a BWD from Carquest. One weel later I replaced the entire Distributor assembly with