Duntov85

Here’s what’s been happening. I will try to divulge everything so as not leave something out that may be important to someone else.
1985 Corvette. Stock original engine. I’ve owned it 12 years. Always starts immediately, even cold.
For the last year when I drove it I noticed a surge at part throttle. Now it’s progressed to really surging at road speed (but only for a few seconds and it may not happen for 200 miles) to outright dying while going down the road, or the freeway. It is now acting like someone flipped the master switch when this happens – just like you flipped the key off , which I didn’t.
Here’s what I’ve done.
O2 sensor (diacom shows data that seems that it’s working correctly.)
New distributor cap, rotor, ignition module, coil - all AC Delco
Tried another TPS sensor. –no change
New sparkplug wires. Multiple sets of sparkplugs. AC Delco and Bosch Platinum.
Cleaned MAF multiple times. (Diacom says 3 GPS with the car off). Burn-off is working! Verified.
Reman ECM – Check engine light had come on with code 41: cylinder select error code. Reman ECM was AC Delco. Never reoccurred since with same calpack and prom.

When the car died a few days ago on the side of the road, I got it started again. Seemed to run fine. Took off down the road. Less that a ¼ mile down the road the engine died suddenly. Got it started by unplugging the MAF. Drove home.
Yesterday, drove 35 miles to work with MAF unplugged. Sluggish throttle response (I’m assuming this is normal?). Bought reman MAF (Cardone brand – NO AC Delco immediately available). Car seemed to run awesome, extremely smooth throttle response. Probably never that good before. Drove home, and back to work this morning. I thought I felt a surge on the way to work, but figured I was imagining it. On the way home, it died on the freeway! I’ve driven this car about 55,000 miles on the freeway and NEVER had this problem. I coasted to the side, the tried to start it. It started right up! I took off, went about ¼ mile, then SAME thing. DIED. I unplugged the MAF and made it home. When I was almost home I was thinking this problem has to be MAF related. Then the car died. I got it restarted while coasting (it started right up). I’m thinking the fuel mixture was probably off – limp home mode kinda deal??
Another odd item is the idle at times will not return to normal when coming to a stop. The throttle is not sticking. Then, when it feels like it the idle will come right down.
Oh, and by the way, the dash has been flickering intermittently. There is no way to predict when it will occur, but it may last 1-2 seconds at freeway speed. The dash was rebuilt by AC Delco in 1997 and has been 100% perfect until now. Not really sure if related or not, doesn’t appear to be by wiring diagrams in service manual.
I’m not really sure what to make of this car. When I first got it in 1997 the dash went out the 1st week. Delco found the problem – it was the computer chip linked to the odometer. They test the unit without the odometer in it, then reinstall it. The dash was in and out 4 times until I called AC Delco and told them to please install a different chip. The other problem was if the timing was set to factory, the engine would ping under hard acceleration (it is a Corvette so you’re supposed to be able to do that – right?) I never figured that problem out, just retarded the timing until it quit. The car was still driveable. A few months ago when I changed out the AC Delco plug wires, I put in the low resistance set with new AC R45TS plugs. The car took off like it NEVER has. AWESOME. Then over the course of one week the power was less and less until it stayed the same. I put in Bosch Platinum plugs. Same thing. Huge power increase, then tapers off. I use R45TS because when I first got the car it would foul R43CTS in 1 week. R44TS in two weeks, and R45TS seemed to not foul and be fine.
The car seems to have a mind of it’s own. I know people have fuel injector problems. This car just seems to run most of the time too well. The emission test report is awesome – better than new cars. Fuel mileage is good. Idle quality is pretty good.
I just can’t drive a car that will die whenever it wants. Surging and running awesome at other times is one thing. Leaving me stranded is not optional.
I’m not even sure where to start.
HELP! Thanks in advance.

jfb

Intermittent engine stoppage and instant restarts is going to be a tough problem to find because you can only find the problem while the engine won't run. Engines need spark, spark at the right time, fuel and air and in the correct ratio and compression in order to start and run. You are missing one or more of these components. I would tape a fuel pressure gauge on the windshield and drive the car and see if you suddenly lose fuel pressure when the engine stops. I would also connect a timing light and drive the car and see if you lose spark when the engine suddenly stops. This is harder, but I would connect noid light across an injector and see if the injectors quit when the engine stops. You can make your own noid light with an LED and a series 680 ohm resistor (from Radio Shack). You have to get the polarity right on the injector wires for the LED to pulse along with the injector pulses from the ECM. One or more of these components has to be missing when the engine stops running but is still turning over while you coast. Good luck.
45's are the correct heat range for your engine.

Duntov85

FRAME 1 (Just before died)
VEHICLE TYPE: 1985 CHEVROLET │ENGINE TYPE: 5.7 Liter V8
──────────────────────────────────────┼─ ─────────────────────────────────── ──
ECM MODE STATUS: DIAGNOSTIC │ECM PROM ID: 7806
══════════════════════════════════════╪═ ═══════════════════════════════════ ══
Engine Speed................ 2000 RPM│ Closed Loop Status.......... On
Vehicle Speed............... 24 MPH│ Fuel Mixture Status......... Rich
Coolant Temperature......... 169 F │ Battery Status.............. Norm
Manifold Air Temperature.... 124 F │ Torque Converter Clutch..... Off
Throttle Sensor Voltage..... 0.98 VDC│ Park/Neutral Switch......... Off
Oxygen Sensor Voltage....... 912 mV │ 3rd Gear Switch............. On
Oxygen Sensor Transitions... 221 # │ 4th Gear Switch............. On
Idle Air Position........... 91 # │ Power Steering Switch....... Off
Air Flow Rate............... 13 GPS│ Learn Control............... On
Injector Pulse Width........ 3.8 mS │ A/C Request................. No
Spark Advance............... 0.0 DEG│ ............................
EGR Duty Cycle.............. 100 % │ ............................
Integrator.................. 120 # │ ............................
Block Learn Multiplier...... 108 # │ ............................
Spark Control Counts........ 37 # │ ............................
NOTE: NO spark advance (it has never displayed a value here even years ago), NO CODES. Also, note vehicle speed and throttle position.

FRAME 2 (when died)
VEHICLE TYPE: 1985 CHEVROLET │ENGINE TYPE: 5.7 Liter V8 ║
──────────────────────────────────────┼─ ─────────────────────────────────── ──╢
ECM MODE STATUS: DIAGNOSTIC │ECM PROM ID: 7806 ║
══════════════════════════════════════╪═ ═══════════════════════════════════ ══╣
Engine Speed................ 5650 RPM│ Closed Loop Status.......... Off ║
Vehicle Speed............... 0 MPH│ Fuel Mixture Status......... Lean ║
Coolant Temperature......... 284 F │ Battery Status.............. Norm ║
Manifold Air Temperature.... 99 F │ Torque Converter Clutch..... Off ║
Throttle Sensor Voltage..... 3.60 VDC│ Park/Neutral Switch......... Off ║
Oxygen Sensor Voltage....... 142 mV │ 3rd Gear Switch............. Off ║
Oxygen Sensor Transitions... 4 # │ 4th Gear Switch............. Off ║
Idle Air Position........... 111 # │ Power Steering Switch....... Off ║
Air Flow Rate............... 32 GPS│ Learn Control............... On ║
Injector Pulse Width........ 0.0 mS │ A/C Request................. Yes ║
Spark Advance............... 30.7 DEG│ ............................ ║
EGR Duty Cycle.............. 89 % │ ............................ ║
Integrator.................. 192 # │ ............................ ║
Block Learn Multiplier...... 0 # │ ............................ ║
Spark Control Counts........ 0 # │ ............................ ║
═══════════════════════════Trouble Codes Detected════════════════════════════╝

NOTE: Trouble code detected. Also note: NO Injector pulse width. Also note RPM and throttle sensor voltage. I did NOT rev the engine. Also note vehicle speed.
HERE IS THE TROUBLE CODE DATA THAT FRAME ONLY!

╔══════════════════════════════════════╤ ═══════════════════════════════════ ═══╗
║VEHICLE TYPE: 1985 CHEVROLET │ENGINE TYPE: 5.7 Liter V8 ║
╟──────────────────────────────────────┼ ─────────────────────────────────── ───╢
║ECM MODE STATUS: DIAGNOSTIC │ECM PROM ID: 7806 ║
╠══════════════════════════════════════╧ ═══════════════════════════════════ ═══╣
║ TROUBLE CODE DISPLAY ║
╚═══════════════════════════════════════ ═══════════════════════════════════ ═══╝
Code Description
(42) ELECTRONIC SPARK TIMING MONITOR ERROR
(53) OVER VOLTAGE
(51) FAULTY OR IMPROPERLY INSTALLED ECM PROM
(45) RICH EXHAUST INDICATION
(44) LEAN EXHAUST INDICATION


Frame 3: vehicle died. Key still on.Note. Trouble code is gone.
══════════════════════════════════════╤═ ═══════════════════════════════════ ══╗
VEHICLE TYPE: 1985 CHEVROLET │ENGINE TYPE: 5.7 Liter V8 ║
──────────────────────────────────────┼─ ─────────────────────────────────── ──╢
ECM MODE STATUS: DIAGNOSTIC │ECM PROM ID: 7806 ║
══════════════════════════════════════╪═ ═══════════════════════════════════ ══╣
Engine Speed................ 0 RPM│ Closed Loop Status.......... Off ║
Vehicle Speed............... 23 MPH│ Fuel Mixture Status......... Lean ║
Coolant Temperature......... 169 F │ Battery Status.............. Norm ║
Manifold Air Temperature.... 124 F │ Torque Converter Clutch..... Off ║
Throttle Sensor Voltage..... 0.54 VDC│ Park/Neutral Switch......... Off ║
Oxygen Sensor Voltage....... 451 mV │ 3rd Gear Switch............. On ║
Oxygen Sensor Transitions... 0 # │ 4th Gear Switch............. On ║
Idle Air Position........... 0 # │ Power Steering Switch....... Off ║
Air Flow Rate............... 3 GPS│ Learn Control............... Off ║
Injector Pulse Width........ 0.0 mS │ A/C Request................. No ║
Spark Advance............... 0.0 DEG│ ............................ ║
EGR Duty Cycle.............. 0 % │ ............................ ║
Integrator.................. 128 # │ ............................ ║
Block Learn Multiplier...... 128 # │ ............................ ║
Spark Control Counts........ 0 # │ ............................ ║
══════════════════════════════════════╧═ ═══════════════════════════════════ ══╝
Next couple frames, nothing really happens different. I was slowing the vehicle to let the laptop hopefully record as much as possible.

Frame 4: Restarting …note pulse width and airflow.
VEHICLE TYPE: 1985 CHEVROLET │ENGINE TYPE: 5.7 Liter V8
──────────────────────────────────────┼─ ─────────────────────────────────── ──
ECM MODE STATUS: DIAGNOSTIC │ECM PROM ID: 7806
══════════════════════════════════════╪═ ═══════════════════════════════════ ══
Engine Speed................ 0 RPM│ Closed Loop Status.......... Off
Vehicle Speed............... 6 MPH│ Fuel Mixture Status......... Lean
Coolant Temperature......... 169 F │ Battery Status.............. Norm
Manifold Air Temperature.... 124 F │ Torque Converter Clutch..... Off
Throttle Sensor Voltage..... 0.54 VDC│ Park/Neutral Switch......... Off
Oxygen Sensor Voltage....... 451 mV │ 3rd Gear Switch............. On
Oxygen Sensor Transitions... 0 # │ 4th Gear Switch............. On
Idle Air Position........... 0 # │ Power Steering Switch....... Off
Air Flow Rate............... 3 GPS│ Learn Control............... Off
Injector Pulse Width........ 5.9 mS │ A/C Request................. No
Spark Advance............... 0.0 DEG│ ............................
EGR Duty Cycle.............. 0 % │ ............................
Integrator.................. 128 # │ ............................
Block Learn Multiplier...... 128 # │ ............................
Spark Control Counts........ 0 # │ ............................
Frame 5: Engine is restarting. Note airflow and pulse width change again. This is the next frame (packet) ECM which is slow delivered.
══════════════════════════════════════╤═ ═══════════════════════════════════ ══
VEHICLE TYPE: 1985 CHEVROLET │ENGINE TYPE: 5.7 Liter V8
──────────────────────────────────────┼─ ─────────────────────────────────── ──
ECM MODE STATUS: DIAGNOSTIC │ECM PROM ID: 7806
══════════════════════════════════════╪═ ═══════════════════════════════════ ══
Engine Speed................ 0 RPM│ Closed Loop Status.......... Off
Vehicle Speed............... 4 MPH│ Fuel Mixture Status......... Rich
Coolant Temperature......... 169 F │ Battery Status.............. Norm
Manifold Air Temperature.... 124 F │ Torque Converter Clutch..... Off
Throttle Sensor Voltage..... 0.56 VDC│ Park/Neutral Switch......... Off
Oxygen Sensor Voltage....... 451 mV │ 3rd Gear Switch............. On
Oxygen Sensor Transitions... 2 # │ 4th Gear Switch............. On
Idle Air Position........... 0 # │ Power Steering Switch....... Off
Air Flow Rate............... 12 GPS│ Learn Control............... Off
Injector Pulse Width........ 2.2 mS │ A/C Request................. No
Spark Advance............... 0.0 DEG│ ............................
EGR Duty Cycle.............. 0 % │ ............................
Integrator.................. 128 # │ ............................
Block Learn Multiplier...... 108 # │ ............................
Spark Control Counts........ 0 # │ ............................

SO, why the spark advance data? Why all the codes? What the heck is going on? IDEAS?

YCarnut

You are describing several problems. Some could be described as drivability issues and the other as a total loss of power. First of all, the assumption is that your engine (rings & valves) is in reasonable shape. A simple compression test can confirm this.

On the drivability problems, when you change the spark plugs, you seem to get a temporary improvement in performance. That would suggest to me that the plugs are getting fouled up pretty quick. The question would be WHY?

Would it be oil or fuel combustion deposits? Well, if the plugs (or just some of the plugs) have after a short time, deposits that look sooty and wet, I would suspect oil fouling most likely from bad valve stem seals. Bad valve stem seals would cause the combustion chamber (head) to get a lot of carbon deposits causing pre-ignition (pinging) under heavy throttle (the other problem you described). Also, I found that this condition will cause surging under light throttle. In the past I tried different fuel additives with little long-term benefit. The only solution that worked for me was to pull the heads, clean them and install new valve stem seals.

For the total loss of power, I would look at the fuel system, specifically the fuel pump. With the engine off, and the pump running, you should see around 46 PSIG at the fuel rail. The pump running current should be around 6.5 to 7.0 Amps. If you have an Amp meter, you can power the fuel pump from terminal “D” on the ALCL connector.

Hope this helps you. When the car runs (well), what is your average fuel consumption?

Duntov85

Normally the MPG indicator reads about 22MPG with some city/freeway driving. It will say 28mpg going down flat level freeway at 60-65 mph staying off the throttle.

I swapped in the original prom today that I removed in 1997. I went 4 miles to the store and back. Almost all the way home it stumbled, like falling flat on it's face. This time it recovered. BUT, the car runs absolutely awesome other than falling on it's face. THEN, after the stumble it always seems to have a problem returning to base idle. The throttle is not sticking.

When I change the sparkplugs they look fine. There is no oil consumption issue. Generally, the engine doesn't knock. All my problems are now intermittent and unpredictable. Compression, etc is fine. Car has 108,000 original miles.

I could send someone the entire Diacom 1000 packet test run with it falling on it's face. It's truly shocking.

What I can tell you about that event. Code: 53 Volts must be higher than 17.1 for 2 seconds at ECM to trigger. Code 42: ECM sees an open or short to ground in the EST or bypass circuit. Code: 44 must be below .2 volts for 20 seconds or more. Code:45 must be above .7 volts for 1 minute or more. Code: 51 Faulty prom. Replaced it with know good prom.

So here's what get's me. How can I get code 44 and 45 if the event didn't even last 20 seconds as show on my Diacom test run? I suppose my alternator could be going nuts, but for only one second? If anything it was reading low voltage (about 12.3 at a stoplight a few days ago, although the warning light didn't come on. The most I ever see it up to is about 14.3 volts).

I'm really puzzled. But I cannot throw parts at the car. That's not the way to fix it.

ROME

Happened to me and it took me a couple month to finally troubleshoot it. The car would stumble like sombody was hitting it in the gut, and sometimes flat out die until the engine cooled off. Problem would come and go and it was impossible to make it happen on command. Left me stranded a couple of times.

In the end I took it over to a mechanic buddy of mine, cranked it up, and he just started systematically laying his hands on everything under the hood. All of the sudden the engine hiccuped and he looked up with a smile. He had found a wire inside of a loom on the front passenger side of the engine that had somehow gotten brittle or chafed and was shorting out. Talk about a relief! We cut the bad piece out, spliced it back together, and it hasn't missed a beat since.

batchman

Note I do not know the vagaries of different years, but just went through a similar sounding ghost on our 88.

> If you lack a fuel pressure gauge, and your logger doesn't pick it up, when the car dies you should
> check the valve on the fuel rail - it's like a tire pressure valve - before you key-on again.
>
> Remember you are releasing fuel by doing this. Don't get it in your eyes or start a fire.
>
> Anything less than a good spray and this is a fuel pump problem. If it's a good spray it's
> ignition/computing. Either problem can be, and from the intermittent nature probably is, wiring related.

^^^ I believe this may be incorrect for your year - it may not hold pressure, intentionally. None the less you are undoubtedly chasing a ghost and a fuel pressure gauge will be your friend.

For us it was the fitting where the fuel pump wiring passes into the filler neck went intermittent. PITA to find!

Good luck,
- Jeff

YCarnut

The 22 mpg is about what I get on my ’85 with similar driving. You have changed out just about everything that could cause your problems (the O2 sensor, new distributor cap, rotor, ignition module, coil, plugs & wires and another TPS sensor). Did you by any chance also change out the pickup coil in the distributor?

Like jfb already suggested, I would try to determine if the engine cutout is related to loss of fuel or ignition. That way you might be able to focus on the offending system. Take another look at your fuel pump. They can fail intermittently, or as with mine, it just quit on the highway without any warning. It was just like turning the ignition switch off.

As a last resort, have a real close look at the connectors and wiring on the engine side of the firewall. On my ’85, I found that the wire insulation near some of the connectors and plugs is starting to shrink back, leaving a ¼ inch, or a bit more exposed. This condition can give you all kinds of strange intermittent conditions.

Duntov85

I'm convinced I don't have a fuel pump problem. Reason: a fuel pump, even if you shut it off for 1 second it should not kill the engine.

How do you explain code 53 which should be triggered by 17.1 plus volts?

I also looked and found a packet where the RPM skyrocked to 6375 RPM (I don't think my engine will even rev that high). The TPS voltage was .94, therefore barely off idle. THAT is impossible. The RPM never went that high.

I leaning towards a couple things. Could the alternator be spiking? Should the voltage go to 12.3 at idle at a stoplight with the lights and heater on? I don't think it should. If you rev it up a little to like 1200 rpm voltage goes up to 13.8-14.2 somewhere in there depending on how long you wait. The car always starts and the battery isn't dead. I just noticed the 12.3 last Friday though.

Possibly the pickup coil in the distributor has problems. But I'd think that part would either work or not work. How could it possibly short out and generate extra pulses to send to the ECM? I suppose it's possible though.

Possible some wires are shorting out somewhere in the engine compartment? What happens to voltage when a short occurs. I don't remember that part of electronics theory.

Duntov85

Ok. So I looked at the grounds. Someone in Scan/Tune suggested look on the bellhousing drivers side.

I found some weird stuff.

please look at the pictures I have and comment.
http://s859.photobucket.com/albums/ab158/Duntov85/

ant-knee470

Well I am no master mechanic, But I just went through something simuliar to what you are going through

The car would run fine, Then all of a sudden Just stumble & die, Pull over to the side of the road & it would crank right back up.. 50 yards or so down the road same thing...
It turns out it was the fuel pump... Just swapped pumps & have not gotten stranded since.. Hope this helps..



Ant.......

YCarnut

The tar like stuff on the connectors came from the factory to keep water out of the electrical connectors to prevent corrosion. When the car was younger (newer), the stuff was more like a jell, but with age it seems to dry up and becomes more like tar.

But the ground wire at the driver's side bell housing looks suspicious. From the picture I can’t tell if the wire insulation broke off due to flexing or local heating due to a poor electrical connection. If it’s a bad connection, then this could very well cause all your problems. In any case, I'd fix it.

Duntov85

So I put in a new AC Delco ignition switch. I tore the other one apart to look inside. It looked worn to me, but should have been functional. Who knows with an intermittent.

I thought I replace the ignition pickup coil just in case it was freaking out every once in awhile. I don't exactly recall, but just about when I had the distributor entirely back together I accidentally wiggled the wire to the condensor (capacitor). OOPS. It moved ALOT. The screw that holds it down looked tight, but it wasn't. I tested the condensor and it seemed to function. I pulled the module out and removed the condensor to check the underside for corrosion or anything like that. Everything looked fine so I restalled it and tightened the screw quite tight. I indexed all the reluctors loosening up the top pickup coil cover and by cutting up four small pieces of .008" brass feeler gauge and inserting them between the distributor shaft reluctor and the pickup reluctor every other one. That way it ended up being exactly evenly spaced all the way around. Turning the distributor by hand it does feel more pronounced now btw.

I must have worked on a smallblock Chevrolet before, because as soon as I hit the key she roared to life. I went to turn the distributor and got zapped barely touching a plug wire. Keep in mind, I've owned this car 12 years and that has never happened.

I think I found the problem. Throttle response seems very good and smooth.

I'm kind of mad I spent all that money, time, and aggravation and it turned out to be something so small. A 10 cent screw!

I learned: NEVER overlook the simple. Don't make it more complicated than it is. Keep it simple, Stupid.

Although, how does a loose capacitor really act?

Duntov85

Well, not so fast. 200 miles later it acted up again. Shifted out of OD even. Drove 70 more miles seems more of less ok. Idle is high and returns to base idle at a very slow response time. I'm at a loss.

SunCr

Go back to when it went haywire and note the Coolant Temp Signal. It's at 284 and at all the rest it's at 169? CTS is used for fuel delivery - if it's spiking up; injector pw will be less; ie, lean if it's dramatically cooler. Hiccups with this many codes are often a bad ECM; but try monitoring the CTS again and see if it is spiking when it craps out. OR CTS, Manifold Air Temp and TPS all share the same ground and they show a dramatic change on this chart. You might want to inspect the harness for an intermittant short to ground - Black at each sensor back to the splice. Have your Scanner hooked up - key on - wriggle each connector/harness and see what the data does.

SunCr

PS - if you don't find anything in the engine compartment, check ECM Pinouts C10 (Coolant Temp Signal); C12 (MAT) and C13 (TPS Signal). Common ground is at ECM D2 but make sure none of the signal Pins are touching anything that can find a path to ground. Slow return to idle can occur if there's an intermittent to ground on the CTS signal - anything above .62 volts and the ECM thinks it's accelerating or off idle, so it won't target Idle until it sees this voltage (or less).