New to forums Hello all,

I just purchased a 86 Camaro with 2.8l. Does anyone know how to test the EST. The guy I bought it off of told me the car runs fine with the EST unplugged. As soon as you plug it in backfires and spudders. Also the tach is inop. Im wondering if the computer isn't seeing RPMs causing all the issue. I pick up the car tomorrow was just wonding on any advise on how to test the EST or even where the signal comes from for the tach.


Thanks

 

Well I can tell you it isn't the tach. Reason why I say this is because MY tach doesn't work properly, it idles at 5k...yea 5k lol.

If I were you I would try to adjust the timing with the EST disconnected then reconnect it once it's set properly. It's the only suggestion I can give.

 

The tach signal comes from the white wire at the ignition coil and goes through the big connector on the driver's side to the dash. Also, the EST tests are done through this wire at the coil.

As for the EST problem, check to make sure that the timing is set to 10* BTDC and not 20+. If the timing is set too early, the engine will run like crap. However, to answer your question, the ECM IS seeing an RPM signal from the ignition module. If it wasn't, well, your engine wouldn't even be running like crap with the EST bypass connected (it wouldn't be running period).

 

I know all about EST trouble. I have this miserable code 42 that just wont go away. Anyway, best way to check the wiring is to disconnect the ECM connectors and the plugs from the ignition module, and hook up a digital ohm meter to it and do a continuity check of the EST signal wire which is white and the EST bypass wire which is usually tan/black. Hook up one probe to one end and the other probe to the other end. Should be little to no resistance. If you have alot of resistance, theres a break in the wire somewhere. A good way to test the module is again with the ECM connectors unplugged, take your test light and put the clip on a source of battery power. That nut for the power cable on the back of the alternator works.(you have to put the plugs back into the ignition module to do this test) And while your ohm meter is still hooked up,(one probe of the meter in the ECM connector end and the other to ground.) Probe the EST bypass wire with the test light. The resistance should jump up to over 2000 ohms. This means the ignition module has "switched". If it does this, your module is good.

 

So i got the car at home. I checked the timing was off the scale. With the tan with black strip wire (EST bypass wire) unplugged i set the timing to 10BTDC. The car ran smooth. Shut car off plugged bypass wire back in. Tried to start the car won't start cranks and back fired thought the intake. Unplugged bypass wire car runs fine. So I started in on 86ttopbird's suggestions. I unplugged the distributer 4 wire and 2 wire plugs. On the 4 wire i ohm ed out the white wire to the tan with black strip EST wire. I had nothing Infinite. So im a little confused. The EST is located where? and were does the white wire meet up with the tan with black strip wire.

 

You may have just fried your ECM doing that. You were taking measurements on 2 parts of the ignition circuit that only have the ICM and the ECM in common. The EST white wire runs between the ECM and the ICM, as does the tan/black bypass wire. You're not supposed to take resistance readings on the ECM circuits with the ECM connected as the current from your meter could destroy the ECM circuits.

Year of car would help as well.

 

No I unplugged the ECM and ICM sorry didn't write that. That's why im confused about what 86TTOP was saying. it's an 86 also.

I was thinking of replacing my ICM and pickup coil but don't know if that would help

 

There isn't supposed to be any electrical flow between the individual wires that connect to the ECM and the ICM. I think he meant that there should be no resistance on each individual wire. Still need the year of your car.

 

1986

 

Apparently, 86 cars had something called a tach filter in between the cluster and the ignition coil, for one. For 2, check the wiring between the coil and the module.

 

Well couldn't located the tach filter. Now tested the 2 wire harness from the coil to the module. There was a little corrosion on the ends cleaned up. Other then that the harness tested out ok

 

Thats why I mentioned unplugging the ECM connectors at the ECM. You simply attach one probe into the end of the ECM connector at the wire your testing. I usually use an alligator clip, then i probe the other end of the wire under the hood. You should have next to no resistance in the wire. The second test involves putting the plugs back into the ignition module at the distributor LEAVING THE ECM UNPLUGGED and your ohmmeter still attached, you probe with the test light on the brown/black wire and see if you get a real high ohm reading. If you do, youre good, you want that if it doesnt, your module is bad. And yes, you are testing both the white EST wire and the brown/black bypass wire for continuity. Of course you do them one at a time. The test light is only for the bypass wire. The white wire does not meet up with the bypass wire, it is a seperate circuit. So is the bypass wire. When you start your car, the ECM watches the reference pulses from the distributor for RPM to increase over 400. When this happens, the ECM then applies 5 volts to the bypass wire to switch the ignition module over to ECM control. Think of this as the ECM telling the ignition module that it will now control all timing events. When your car is cranking, it is running strictly on the advance built into the ignition module. The EST signal is grounded until RPM over 400 is seen by the ECM. Also i was re-reading your original post where you say when you plug the EST connector back in it sputters and pops. Have you checked the base timing with a timing light? If the previous owner took out the distributor it could be a tooth off. If it was 180 out, i doubt it would even fire. Or it could even be severely retarded or advanced. Youll know something is wrong when you cant see the timing marks on the balancer(they are just slots in the balancer ring. Mine was the larger one) with the timing light. Heres a flow chart for doing the checks i mentioned.

 

I think I may have described it wrong. The car does have a code 42. The reason it has a 42 is because the bypass wire is unplugged. I went through this http://www.asashop.org/autoinc/may97/techtips.htm and found no issues Now the car runs with the bypass wire unplugged. If i clear the computer and plug the bypass wire back in. The car cranks tries to fire. What I think is happining is while its trying to fire the EST is switched on because the car kinda starts but as soon as the EST is switched on the car back fires a little thought the intake (advancing too far) and stalles the car. There is no codes at this point and the car never runs until I unplug the EST bypass wire and i get a code 42. Now i have set the base timing by unpluging the bypass wire and setting base timing to 10BTDC. It's like the computer is telling the coil to advance way too far. Do you know what sensors are used to tell the computer how far to advance?

 

The ECM gets all its ignition information from the ignition module. The reference pulses tell it RPM,crankshaft position, all that. Based on MAP or MAF signals for load, the ECM either advances the timing or retards it. There is a small amount of advance built into the module itself. It is what is used during cranking and when the code 42 sets. It really sounds like your distributor is a tooth off. Bring number one piston up to top dead center on the compression stroke. An easy way to tell is to put a finger over the plug hole(after you remove the spark plug of course) and turn the motor over by hand. When you feel air pressure on your finger you know youre on the compression stroke. At this point, I usually put one of those large drinking straws through the plug hole. It will rest on the top of the piston. As the piston goes up, it pushes the straw out. Turn the engine over slowly by hand until you see the straw start to drop back down, then reverse it a hair.(the reason i say use a drinking straw is it is less likely to damage the piston or cylinder wall than a screwdriver) This should be top dead center. Next take off your distributor cap and note the rotor position. It should be pointed at the number one cylinder terminal on the cap. Too far left or right will give you problems. If all is well there, then i would try replacing the module first. While youre under the dizzy cap, take a good look at the reluctor wheel. It should be a round magnet wheel just under the rotor. Make sure there are no cracks or corrosion on it. If a new module doesnt solve your problem, then you may have a bad ECM. The reason i say try a new module first is its generally cheaper than buying an ECM.

 

alrighty ill give that a goo today. Ill let you know. Thanks all for the help

 

no problem. I just went through all this with my car. Ended up replacing the whole distributor with a reman.(i kept getting a code 42 the reluctor wheel was cracked and you cant buy just the reluctor) The distrib hold down is a real PITA though. If you have to take the dizzy out to reset it, you will probably have to give it a few tries to get it back on.

 

well just replaced the Ign. Module which wasn't fun. I also did a coil because the other one didn't look to healthy. Still having issue. Now the only thing that isn't common from bypass mode and running off ECM is the white wire. So I tested that wire again. tested ok. I just ordered a Used Ecm from the local junkyard. Same car all the same options. Will pick it up later this week. Hopefully this takes care of the issue.
Ill keep everyone posted. Thanks all for the help. Im crossing my fingers.

 

How many notches do you have the timing set at on the timing tab? Each saw tooth pointing towards the balancer is 4 degrees: 4, 8, 12, 16, etc. The timing should be set just after the second saw tooth, not at the end of the scale.

 

yup thats what i was referring to earlier. It's a bit tricky on these cars to set the timing correctly. Heres an illustration of the graduations on the timing pointer.

 

And, actually, the only difference between EST and non-EST is the tan/black wire, which tells the ECM to stop sending the EST signal for setting timing.

 

Ya i got the timing set right. Between 12 and 8. I even had two other people check it. Everything else tests out ok so that's why i just decided to buy a used 100% working computer. Im out of options I can't see it being anything else.

 

Here's something to try. Completely disconnect the 4-terminal connector from the ICM. If the engine runs, the FSM says there is a problem with the pickup coil not putting out a good enough signal for the ECM. (Chart C4-B)

Also, before tearing the dizzy apart, check ALL of the other wires in the 4-wire connector, especially the black/red one, and the wires running between the module and the coil as well. Clean the dizzy base under the module REALLY good until it shines as well.

 

You gotta watch that reluctor magnet though. They have a tendancy to crack or break when driving the roll pin out of the dist gear.

 

Another thing: For both of you, using a DMM on the 2VAC scale, check the voltage coming out of the pickup coil during cranking. This voltage is supposed to be above a certain threshold for the pickup to be considered to be working properly. I think it's around .4VAC, but I couldn't swear to it. I'll measure mine when I get back from work in the morning and let you know. The meter is set on AC because of the digital on/off signal the coil puts out, and the VDC scale will only read half of this.

 

or just ohm out the pickup coil through the plug :P

 

Nope... The key is checking the output, not the resistance.

 

you are checking for continuity between the pickup coil and the dizzy body. If there is, its shorted to ground. But yeah checking current output is a telltale sign as well. If all this helps this guy get his car fixed, maybe we should sticky this thread. That darned code 42 is a real PITA in these cars once it starts settling in. Oh I wanted to mention, hey Flintman, when you put that new ignition module on did you put the silicone di-electric grease under it? That is a must or the module will burn up.

 

Now looking at wiring diagram. During bypass mode the pickup coil feeds the ICM which the ICM will boost the signal and send it to the computer and the coil. Which will tell the computer to fire the injectors while the ICM controls the base timing of the coil. Now if not in bypass mode the same thing happens until the computer sees over 400RPM which then in-turn switches the solid state relay in the ICM to look at computer to fire the coil off. While the pickup coil still sends the signal to the ICM but instead of heading to the coil and computer it just heads to the computer.

Let me know if im wrong here please.

So if the car runs in bypass mode just fine that tells me the pick up coil is fine, the signal to the computer is fine (because the injectors are firing), the wiring from the dizzy to the coil is fine, and the only other possibility would be the white wire or the computer. I already replaced the ICM.

86ttop I cleaned the base and applied the grease to all connections even the base

 

The ECM will not fire the injectors if it doesnt see a reference pulse from the dizzy because it wont know the engine is cranking. The injectors are however a completely different circuit though. The pickup coil is what sends the reference pulses to the ECM. In bypass mode, the ECM is controlling the timing. That is the coil is now being triggered by the altered signal being sent out from the ECM. If there is a problem in that circuit, the ECM will remove the 5 volts from the bypass wire and turn the timing control back over to the module. This sets the code 42. You will be running on module advance only. There is relatively low voltage on the white signal wire. Something in the neighborhood of 300 millivolts. The ECM expects to see this low voltage on that wire. If it sees too much or nothing at all(EST wire is open or grounded) it removes the 5 volts and sets code 42. One more thing id like to mention, if your spark plug wires are too close to the EST and bypass wires, they can cause electrical fields to develop in those wires and cause the ECM to set code 42.

 

Ya that I understand the only reason I have a code 42 is because I have the bypass wire open. I just wanted to know if what i typed in was correct on what's happening. I have trouble explaining things Im sorry. Let me try it a different way. So if I had a problem with my pickup coil the car wouldn't run in bypass mode or any mode. If I had a problem with my ICM (Well I have had some wierd stuff happen here) there could be a few things because of the different circuits inside. But this is new. If I had a problem with the reference wire going from the dizzy to the ECM then the car wouldn't run because it doesn't know that the engine is cranking and wont fire the injectors. If I had a problem with the white wire then the car would run fine in bypass mode but not when the ECM is controlling the timing. Which this wire tested out ok. So the only other possiblity would be the ECM not sending the right signal out.

My problem is the car doesn't run when the ECM controls the timing so I have it in bypass mode which is the code 42.

 

If the ECM was not seeing a reference pulse from the dizzy, the engine wouldnt run, period. I still think that either your ECM is bad or your timing is not set right.

 

Ya I too believe it to the the ECM I ordered one will be here Thursday. I just wanted someone else to confirm what I thought it was. Ive checked the timing muilti times. I even had my farther-in-law (ex mechanic) check the timing. Ive load tested all the wires they were fine. Replaced the ICM tested Pickup Coil. So I think I have all avenues covered. Thanks All for the help Ill let you know when I install the new ECM

 

The thing is that the FSM has somewhere around 4 separate charts for the ignition system, "Engine Cranks But Won't Run (2x)", "Code 42", and "Ignition System Diagnosis". Your problem, as you described, is that the engine won't run properly with the bypass wire connected between the ECM and the ICM. The step 1A on the "Ignition System Diagnosis" chart, C4-B, is to disconnect the 4-wire connector at the distrbutor and see if the engine runs. If it runs, like I said, the flow chart says to replace the P/U. It may be that the coil is good, but, like 86ttop said, the magnet could be cracked or broken, which results in a bad signal. If the P/U is sending a junk signal, the ICM may be allowing the engine to run, but the ECM is seeing a nearly useless signal and firing the coil off at the wrong time.

I'll see what I can do about getting the C4-B and the "Engine Cranks But Won't Run" charts posted.

 

Thats confusing my now if I unplug the 4 wire out of the dizzy then the car won't start. I tried that before. but the reason why it doesn't start is the ECM doesn't get the signal to fire off the injectors. I think Ill wait to see if the ECM solves the problem it if does im all set if it doesn't then it has to be the pickup coil which tested ok but you never know.

 

If the engine wont run with that 4 wire plug disconnected, then I'd say the PU coil is ok. You did check your reluctor wheel for cracks right? The new ECM will probably fix your issue. That is providing its good too lol.

 

Yeah. Sorry about that. Yeah, duh... The ECM can't fire the injectors if it doesn't see reference pulses. The FSM says to check for spark.

Either way, if the ECM doesn't fix the problem, at least you have a spare.

:edit: I'll try to get some pics up tomorrow... I have like 300 or so pics to take, between both service manuals, since I don't have a scanner.

 

Im hoping my ECM takes care of the issue if not im putting in a new dizzy. I really don't want to do that its stuffed way back there the ICM was fun to change I can only image trying to pull the dizzy out and line it all up.

 

All you need to do to line it up, when the engine is running on 10* base time, is to make a mark of where the rotor points in relation to the plate when installed, and another where the rotor is pointed when the dizzy is loose from the cam gear. For the replacement, line up the rotor at the first mark (should be to the reverse of rotation of the second mark), and put the dizzy in the hole. When installed, the rotor should line up with the second mark.

 

lol well Ive got a spare computer now. New Dizzy will be here friday will replace saturday. I hope that's all. The new Dizzy comes with a new ICM too. Im going to try to return my other one.

 

Probably too late now, but I wouldn't return the module you just bought merely because you are replacing the dizzy. You never know when the ICM is going to go bad, and it only takes 5 min to swap it. I know a number of guys who carry spares in various glove boxes (depends on what GM they are driving) for when the things crap out.

 

Ya good idea. I still have it. After I replace my dizzy this car better run right Lol.

 

New Dizzy installed Still same issue.

Recap: Replaced ECM, Coil, Plugs, wires, Dizzy, and ICM. So after all that I still can't plug the bypass wire in. The car runs awesome with the bypass wire disconnected. As soon as I plug it in and start the car well she doesn't start. Tries to but stalls out and blows smoke out the intake. Now if I clear the ECM and start the car with the bypass wire plugged in No codes what so ever. What sensors control the timing? Maybe bad knock sensor? Im pulling at straws now. I miss my old 1974 laguna points ignition simple LOL. Any more help would be gratefully appreciative .

THanks

 

Knock sensors weren't used on the 2.8 RWD, only FWD. RWD didn't get one until the 3.1 and the 730 system.

Did you check out that tach filter thing?

 

I tried to locate with no luck. Not sure if I have it. Would that effect EST ? I thought the filter just makes the tach a little smoother.

 

I'm going to post up the C4-B chart. I don't know how much it's going to help you. The best thing I can say is check the VOLTAGE on all of the wires at the 4-terminal connector EXCEPT the purple/white wire. Should be .76V on the black/red, and 5V on the tan/black and the white wires. Disconnect the white wire from the tach connector (will be in the gray harness connector at the ignition coil, follow the white wire to the tach connector), and check for switched voltage there as well.

:edit: Probably be best to start at 3 in the chart, since you have spark.

 

Everything Tests ok. I even did it twice to make sure

EDIT: I put a logger on the white wire to see if the ECM is sending the signal. The ECM is sending the signal to the Dizzy but it's way to far advanced

 

That's really weird... It's almost as though your engine wants to start with the plug wires on one set of cap terminals and run with the ECM on the set to the right.

Has anyone altered the stock PROM program? (That you know of)

 

not that I know of. I tired two ECM's both have different chips.

 

What does the new dizzy look like? We had one at school that looked almost the same as the one pulled out of the engine, but it didn't work worth beans. The only way that test engine ran was to swap the new module into the old distributor. But that one had a dead module. Can you get a pic of the old and new distributors? I'd like to see the pickup coil connection on the old one.

 

Well the old Dizzy def had issues. I didn't really notice anything inside when I replaced the ICM because its stuffed soo far back. But when I got it out there was more rust on everything and the wires coming out of pickup coil didn't look too good. Def original. See what gets me is the car runs completely fine with EST unplugged. Which is telling me a lot of the stuff is good. Im thinking about running a new white wire from dizzy to ECM. That is the only thing that isn't common to both bypass mode and EST mode. I load tested the wire and it tested ok this is why im not thinking it will help. But i've tried everything else. Do you know what sensors are used to tell the ECM to advance the timing? Ive looked thought every manual I have. I wish I had one on just the ECM and all its logic.