Battery negative cable, battery connectors replaced

Replaced the battery connector hacks with a pair of proper connectors that attach a Euro-style battery (terminals on top) to US-style wires. Cleaned up all the terminals & connectors.

Replaced the ground cable from the battery to the engine block.

Opened and re-tightened the TBI mounting bolts to correct torque (22 Nm).

The coolant fan switch cable is disconnected (and covered with tape), since I don't have the new connector yet. I tried grounding the wire (with the engine off, battery connected). As I understand this should have started the fan, but it didn't.


Nothing has changed. The car starts well when it's cold, but after 10-15 minutes, it starts to choke violently and the engine dies off. All coolant and engine temperature look normal in WinALDL.


8th spark plug replaced, knock ^H^H^H^H coolant fan switch connector damaged

I finally managed to lift the car up and replace the cursed #8 spark plug. Now all plugs are new AC Delco R45TS gapped at 0.89 - 0.99 mm. Of course #1 - #7 are half a year and a few 100 km older, but you can't have everything.

While I was working on this, I tried to inspect the knock sensor coolant fan switch connector that lives near the #8 plug. The plastic around the connector simply shattered into pieces before I could detach the wire. I was left with just the connector's metal pin hanging from the wire.

Update: apparently that wasn't the knock sensor, but the sensor that controls the coolant fan. The connectors are nearly identical though...

It's surprising how bristle that connector is, knowing it's subjected to temperatures between -30 and +100 or even more, water, grime, etc.

New connector, knock sensor and knock sensor module (ESC) are on their way. Due to the transport costs from the US to Europe, it's always cheaper to order more parts at once.


Battery terminals cleaned

Took apart the US-eur adapter in the positive battery terminal and cleaned it.

I also replaced the positive battery connectors in the junction block next to the battery that connects the battery, charger output, (???) fuse and a 4th wire with a fusible link.

Cleaned up some of the cables.

Cleaned and reattached the battery -> chassis ground cable.

Golan fuel filter cleaned

I cleaned the fuel filter.

Most junk was around the small metal screen on the intake side, even though this stuff looks like is fine enough to pass that screen. I guess due to the diagonal installation position, the stuff slowly drips off the main filter screen and collects on these edges.

Another shot of the intake side

Exit side looks clean, except...

For these particles under the O-ring. So apparently these particles are small enough to pass the filter.

I soaked the filter screen in paint thinner & rinsed it under running water, but I didn't see any dirt coming off it.

All assembled, including the pipe fittings

Mounting point


A couple of videos demonstrating the problem. On idle, but the symptoms look the same on the highway as well.

91 Firebird TBI, bad idle, starting w/ charger off

91 Firebird TBI, bad idle, starting w/ charger off, w/ EST bypass

(not embedding the clips because loading them would take forever)


More engine trouble

So after the last datalogging session, I did another test drive.

Everything mostly normal, except..... when cruising at 80-100 km/h (50-60 mph), the engine started acting up like crazy. Stalling, choking, tachometer jumping up and down, etc. Not just the tachometer and engine, but the car itself would also slow down, accelerate and "jerk back and forth" at the same pace with the engine. So apparently the TCC was locked when this was happening.

I pulled out from the "highway", stopped the engine and tried to start again. It started roughly; choking, stalling, etc. After detaching the EST bypass cable, I was able to drive it home carefully. The engine seemed to run better with the EST bypass disconnected, but I can't tell if it was normal for that condition. The exhaust sound was more "bubbly", and I didn't see the tachometer jumping around anymore.

Datalogging, ignition/electrical bugs

I think I've spotted the gremlins in action.

I took some data logs using the venerable WinALDL during my test drives (on 2013-05-04 and today, 2013-05-08), but I only bothered to analyze them now. The graphing software I used for these pics is called ALDLView.

Logs from 2013-05-04

This time I had the crappy ignition coil in.

The battery voltage drops intermittently and often. I suspect these are the same incidents when I've seen the SES light flash and/or the tachometer jump wildly.

If we add more variables and zoom in, we'll see that all values drop to zero simultaneously. Here are Speed (VSS), MAP, RPM and O2 readings in addition to Battery Voltage.

In the second incident, the VSS jumps to 180, but in most of these it drops to zero as well. This matches what I've seen the speedometer do: most of the time it shows a realistic value, but a couple of times it's jumped up randomly.

Here's a sample of the "DRP Occurred" signal (Distributor Reference Pulse). I find it odd that it DRP frequency doesn't correlate with engine RPM.

Logs from 2013-05-08

I made another 16 km (10 mi) test drive today. This is after putting the original ignition coil back in & replacing the vac hoses.

There were only 2 voltage drops, and they happened while the car was still idling on the lot (pic below, speed zero, CTS rising). All in all performance felt "normal", there were some random tachometer jerks still.

2nd part of the test drive. The battery voltage didn't drop at all (according to the ECM), so ALDLView scales the white line differently.

I saw one SES flash, though. This happened on WOT (wide open throttle) acceleration in the middle of the graph.

Here's a closeup of the WOT part, i.e. where TPS (throttle position sensor) jumps to 100%. The speedometer also jumped almost 45 degrees upwards and the tach was acting up. The car accelerated nevertheless (yay). Right before flooring the pedal, I saw the tach jump a couple of times, this might match the two minor voltage drops just before the WOT part.

Maybe the acceleration itself shook some contacts loose and this caused the ECM to reset for a short moment?

Also, here's another graph of the DRP flag:

Odometer: 225 974 miles.


Vacuum hoses replaced

I decided to replace the vacuum hoses to be on the safe side. However.... even though I specifically asked for vacuum hose, and the clerk at my local (read: only) parts store acknowledged that I was, indeed, requesting vacuum hose, only after returning home did I realize that I'd been sold...... fuel hose. Apparently I should have checked the markings on the hose at the counter. WTF is wrong with people?

I installed the new hoses nevertheless, since some of the old vacuum lines were really worn out.

Old hoses:

  • 5/32 GM6148M 042490 ADP (~ 4mm)
  • 5/32 GM6148M 042490 PRC (~ 4mm)
  • Some unlabeled piece (5-6 mm?), between intake manifold and a valve that connects to the A/C vacuum system

New hoses:
The flexible vacuum "pipes" that connect e.g the MAP sensor and the EGR solenoid I left in place.

Odometer: 225 974 miles


Ignition Coil Trouble

Lesson for today: don't bother with "closeout", "white label" etc. products.

After replacing the ignition coil, I found out the terminals on the part I received from RockAuto are simply too small for the primary coil connectors that are supposed to plug into the coil, even though it's a supposed to be a compatible part. I ordered a Standard Motor Products DR-37, but what they sent was labeled "ProFire UltraPower DR-37".

The difference is down to a 0.4-0.6 mm, but it's enough that the connectors simply won't stay in place. 

Also, the openings for the actual contacts are 1,5 mm wider and shaped differently.

It was a bit of an effort to convince RockAuto that the part really was incorrect. Eventually they agreed to refund the $23 I had paid, even though the part had only a 30 day warranty. So, I have no complaints about their customer service.

Action taken
* Put the original ignition coil back.


* The engine runs much better. I was able to complete a 30+ km test drive without any stalling or choking -- when you're cruising at < 50 mph everything seems mostly fine, but during WOT acceleration there were still a couple of SES flashes and back/misfires.
* Towards the end of the test drive, I had cruise control set to ~55 mph adn there was some weird, repetitive jamming / halting action going on. Is the TCC trying to engage and failing? Or Highway Lean Mode failing?


Distributor & ign. connector replaced, timing reset; better but not good


Action taken
1) I've replaced the whole distributor with a Cardone Select 841830.

2) Also, the gray connector on the ignition coil needed replacement, since the holding clip on the old one was broken. Apparently this connector is responsible for carrying current from the ignition key (pink lead) and supplying a signal to the tachometer (white lead). I used a Standard S562 i.e. this thing...

... only to find out that the bloody connector will not stay on the ignition coil it was meant for.  The plastic clip is too loose and simply won't hold the connector in place, and the white styrofoam cushion/seal inside the connector is too thick, so it pushes the connector out of the socket. WTF? Both the connector and ignition coil are stock replacement parts from Standard Motor Products. It got a bit better after replacing the styrofoam piece with the flattened-out piece from the old connector, but it's still loose and you can detach it just by pulling. So I used electric tape to keep it in place. --> update: the coil was faulty, not the connector - see the next post.

3) I readjusted the timing to what might be the factory default. I haven't found reliable documentation on what values the timing  marks stand for, but now it's set like this:

The same symptoms persist as before, but now my tachometer is dead most of the time. Apparently white lead, or the tachometer connector it attaches to, is even more unreliable now.

The symptoms are less frequent though, I was able to complete a 25 km (15,5 mile) test drive without the engine dying at all.

Also, I noticed some stutters / surges while driving at about 100 km/h (60 mph). Another halfhearted guess, is the TCC trying to engage and failing?