The new life of the formula fastback

[GTRS Fiero]

It will be interesting to know how the cylinders look, when you pull the heads.

[NoMad]

From the abrupt on to off throttle response I have now I could also be jumping to conclusions and have a ruined cat/muffler issue but I will know more Monday when I have time to get the car in and drop the exhaust.

[GTRS Fiero]

You could just remove the EGR valve to test that.

[NoMad]

EGR is already blocked off. And the exaust has to come down anyway.

[GTRS Fiero]

If you remove the EGR block-off plate, there should be enough exhaust flow to determine if the issue was with the cat back.

[NoMad]

And the surge is back in a different way....

Exhaust comes out in the morning so I can try to sort this out.

[NoMad]

Also just paid for my second '88 cradle. This one is partially boxed for strength, really nicely painted, and comes with the lightweight eyelet connecting rods and thw dropped link relocater for lowering the car. This should allow me to really start moving on the TDC. Now to decide if I try my hand at rebuilding the getreg or farm that out....

[NoMad]

Dropped the exhaust today. Nothing blocking the cat but some rattling of material in the muffler. With the cross over open and reving with no load there was some back firing on closing throttle as if it were rich but the plugs don't seem toindicate that, if anything it seems a little lean from the plugs.

Scince it is down anyway and thw cat is cut out I will replace that with straight pipe and do some clean-up. Not sure on the muffler but I will look at replacement options just in case.

I am starting to feel Really stumped here.

[GTRS Fiero]

The rich/lean should be the O2 sensor.

How does it run, under load?

[Fierofool]

And the o2 sensor won't always set a code, either. 

[NoMad]

Well it had been running well between surging episodes but I have been fighting this intermittent surging for long enough I am starting to doubt my own sense of well running.

Welded up and painted the exhaust save for the final joint. Will get it all hung and tacked before the final drop and weld. I am not a good welder and my buzz box isn't laying down solid beads on a 15 amp circuit and mine are still better than some of the ones that were on this one. Rewelded all the partial seams and ground the spatter and globs back before the paint. Likely this system will very much be temporary.

Will see what happens when I get it back in without the CAT. Will probably drop a new O2 sensor for good measure since it isn't something I can really test like the other items. 

Each "solution" seems to be making it a little better but I really need to lick this soon.

Cradle and parts should be here this week so I can start getting the DOHC ready to go.

Really thinking more and more that a Megasquirt 3 system will be my ecu rather than a 7730. I want to go to non-waste spark to add in some tuneability and reduce the heat/wear on the coils. That and the turbo plan make tunning the MS3 seem like a much better option for not much more money.

[GTRS Fiero]

For this surging, do you feel it, or just hear it?

If you are on cruise, does your speed change?

Is the surge at set intervals?

[NoMad]

No cruise. It is a bogging as I apply power but only when the motor is hot. Not just warmed up, but really good and warm. Once I let it cool it goes back to normal. This last on set was a bad enough loss of power that I was struggling to make small pedal adjustments to stay at highway speed without it bogging and surging so bad it felt like it was going to stall. Stopped and had dinner to let it cool and was fine for the drive home.

[GTRS Fiero]

It sounds as if it may be overheating.

[NoMad]

Well I think I might have all the tail chasing somewhat sorted.

Car went back together this morning to take me to work. Did a full out stall at 70+ going south on 75. Lots of honking and angry gestures as I tried to get to the right side. Pushed in thw clutch to confirm and it showed 0 rpm. For diagnostic purposes I turned the ignition off then started the car while still rolling with clutch in. All symptoms gone.  10 miles later it started acting up again so I did the off-on trick. Cleared the problems a second time.

So basically I Should have called IT so they could tell me to turn it off then on again.

So an ECM is the likely culprit.

Also did it on the way home and same off and on cycle cleared it up.

That was a ton of trouble shooting, time, and money all spent only after following proper steps and research to find out it was the computer...

Reaffirms my plans to go MegaSquirt3 rather than a pick and pull 7730 or other gm ecm for the LQ1 swap.