Replaced knock sensor, cleaned out radiator

Lesson for today: in a small-block chevy,


For fuck's sakes. I don't think there's any technical reason it should be connected to the coolant passage.  The wisdom at thirdgen.org suggests GM simply cheaped out and re-used an existing drain plug for the knock sensor.

GM's shop service manual, chapter 6E2-C5-1 - "Electronic Spark Control (ESC) System" does not mention anything about this. For the benefit of future generations, there should be a step 3.5 under Remove or Disconnect, namely "Prepare to swim in coolant". At least the stuff wasn't hot anymore.

Anyway, there's now a new knock sensor. Apart from some wiring harnesses, all ignition parts are new/replaced.

Since most of the coolant ended up on the driveway, I had an opportunity to flush the radiator, coolant reservoir etc as well. This actually came at a good time - there was a hideous amount of sludge in the system. Apparently I had messed up the coolant/water ratio last year as well -- the liquid had frozen during the winter and now coolant was seeping through the water pump gaskets. The pump will be cleaned and new gaskets installed, if I can manage to pull that thing out.


ESC module changed; Isolating the ignition problem

I've replaced the ESC module. Now almost the whole ignition system is new - except for the knock sensor and some wiring - yet the same problem persists. Here's a another home video showing the problem.

However, I've managed to narrow it down. If the EST bypass (aka set timing) connector is open, the engine runs just fine! The ECM sets error code 42 and the SES light comes on, as should happen when the connector is open.

So, the problem is somehow related to how the ECM controls spark timing.

Last time, I had set the spark advance to "apparently 0", like this:

In this position, when the bypass cable is disconnected, the engine sputters a bit and feels like it's hesitating on idle. So I rotated the distributor until the idle sounded smooth and stable - the timing is now on the last tooth:

            /           |
                 v v V V   O

I haven't seen _any_ of the tachometer flip-outs, stalling, sputtering etc when driving like this. The power - what little the stock TBI has - is mostly present too.


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?


Pick-up coil replaced, no help

Action taken
Replaced the pick-up coil inside the distributor

No changes; symptoms remain.

Since changing the coil involves taking most of the distributor apart, I got a chance to clean it more thoroughly. Looks like the magnet has fractured in  at least three locations. 

Also, this clip was quite helpful - http://www.youtube.com/watch?v=K5QRK9VZwcM


Spare part lottery II

Action taken (Apr 12 - 20, 2013)
  • Distributor cleaned, pulled out and cleaned some more
    • A lot of dust, rust etc under the distributor cap
    • Also, there were some mysterious black flakes on the distributor shaft, but they didn't seem metallic. They don't react to a magnet, and break when you crush them with your fingernail.
  • Ignition Control Module (ICM) in the distributor replaced (Standard Motor Products LX340)
  • Ignition Coil replaced (Standard Motor Products DR37)
  • ECM & its PROM chip replaced (original part, ordered from an eBay merchant in California, pulled from a 1992 Camaro, )
    • PROM version is "AXKT", while the original was ANTT. As far as I know, AXKT is just a compatible upgrade.
  • Battery negative terminal connector replaced
    • The threads attaching the cables to the old connector were gone, so this might have caused some contact issues
  • Grounding cable between battery and chassis replaced, contact point in chassis cleaned
    • Grounding cable between battery and engine block was left in place, looks "ok"
  • Battery terminals and connectors cleaned
  • Wires to the Heater / AC blower motor disconnected
  • Wires to the AC compressor disconnected
    • I don't know what condition the AC is in, at best it's very low on refridgerant

Distributor Shaft

I had hoped that blindly replacing most of the ignition-related parts would take care of this problem, but the same symptoms that I had last fall are still there. I think things got a bit more reliable after I fixed the battery contacts and disconnected the heater/AC blower motor, so bad grounding and that worn-out motor were probably at least part of the problem. Still, this only lowered the frequency at which the symptoms occur.

I made a test drive of about 9 km today (5.5 miles), and the car died / SES'd maybe half a dozen times.

Next up, I'm looking at
  • Replacing the distributor Pick-up Coil (since I already have a new spare part)
  • Replacing vacuum hoses
  • Replacing the whole distributor (at about the same cost as all those distributor parts above....)
  • Replacing the grounding cable between battery and engine block
  • Checking / replacing the cable for the VSS (Vehicle Speed Sensor) 
  • Replacing that 8th plug...

And possibly
  • Checking the fuel pump wiring
  • Replacing the TBI injectors

If none of this helps, it looks like I'll have to switch my brain on, do a bit of homework and actually try to diagnose the problem in a structured way.

Running trouble, Spare part lottery

[backdated for chronological order]

Recoup of the mysterious running issues that started last fall.

  • "Service Engine Soon" light flashes randomly when driving
    • This happens very often when you hit a bump, but it also does it randomly on an even road
  • "Security" light flashes less randomly when driving 
    • (referring to the VATS chip in the ignition key)
  • Tachometer jerks up and down randomly, maybe +/- 500-1000 RPMs
  • Speedometer jerks less randomly
  • Engine dies semi-randomly when driving or taking off
  • After the engine has died, the SES light sometimes stays lit, other times it's off
  • No error codes given by the ECM, ever, despite the SES light

Steps taken last autumn (Oct 2012):
  • Switched from E85 (Ethanol) back to E95 (Regular Gasoline)
  • Injector cleaner stuff added to gasoline
  • PCV Vent replaced (Standard Motor V178)
    • old one was making a rattling noise, although it was less than 6 months old
  • TBI injectors and their filters taken out and cleaned with a carburetor cleaning spray 
    • Stream from the injectors looks clean, stable and has a conical shape like it's supposed to.
  • Spark Plugs 1-7 replaced (AC Delco R45TS
    • Plug no. 8 was impossible to reach in the freezing weather....
  • Spark Plug Wires replaced (Standard Motor Products 7850)
  • Distributor Cap replaced (Standard Motor Products DR468)
  • Distributor Rotor replaced (Standard Motor Products DR326)
  • Battery replaced (62 Ah)

Some late updates

I realized I haven't updated this blog since last summer.

I did finish replacing the fuel lines in August 2012. This was a much bigger undertaking than I had imagined, not least due to crappy (or nonexistent) tools and having to do all the work on an open parking lot. Having finally gotten all the pipes bent correctly, hydraulic hose fittings, fasteners, etc. installed etc, I didn't have much motivation left to document the whole process. Pictures and details will be coming soon-ish, though.

In August-September 2012, I also acquired a chip, calibrated for E85 Ethanol fuel, from a friendly hobbyist who has invested his time in getting TBI engines running on this stuff (amongst other things). To our mutual surprise, the car started immediately after filling 30l of E85 and replacing the chip. A couple of calibration runs were made using WinALDL, and new chips burned based on the results.

In civilized temperatures (15+ C) the car started and ran normally on E85, the only difference being a slight vinegary odor in the exhaust - and of course slightly higher fuel consumption per volume. When the temperatures started to drop below that 15 C mark, a lot of problems starting and running on a cold engine appeared, though. The chip needs some further calibration to deal with cold temperatures that we weren't able to finish.

Finally, in September-October 2012, some weird running problem appeared where the tachometer would suddenly jerk up or down about 500-1000 RPMs. This was sporadic at first, but rendered the car undriveable within a couple of weeks. It started after the spark advance was adjusted, and since the ECM had been lying in the passenger side footwell for about a month, my main suspects have been ignition and the ECM. It could just be incidental, of course. I tried changing the spark plugs, spark plug wires, distributor cover and rotor in the autumn, but none of this helped.