ishootstuff

So I'm in the last stages of repairing the packrat C4 and I have no spark unless I "hotwire" the BAT terminal on the distributor cap.

There are a few connectors that the plastic part has been chewed away. I was hoping one of you experts could tell me what these are. I have done lots of googling and came up empty. The only white wires I can find in wiring diagrams in the engine compartment are related to anti-theft and tach signal. Anyway, HELP!

vetteoz

Unit you show is the tacho filter ,
there is a corresponding brown connector on the wiring harness that connects to one end ,
the other end goes to the TACH terminal on the dist cap
Filter is typically mounted under top trans bolt drv side


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ishootstuff

Thank you so much for the immediate response! I assume this has nothing to do with the no spark? I read that it needs oil pressure to keep running, but I'm new to this system. Thanks again.

vetteoz

I would be back tracing the coil circuit ( pink ? wire at dist cap ) to the Ign switch to see where you loose power ( or if you even have power from the switch )

cohocarl

Yup, but that's an oil pressure switch for the fuel pump. Wouldn't have anything to do with no spark. When you turn on the key, there should be about a 2 second "prime" out of the fuel pump, then after the engine starts, the oil pressure switch keeps the fuel pump going.

ishootstuff

I can smell raw fuel, so I'm pretty confident that part is good. Using a timing light, I confirmed no spark unless I force feed her. It had spark before I replaced the engine, so I have to assume I wired something incorrectly. That packrat left me quite a mess.

Cliff Harris

The oil pressure switch is a backup in case the fuel pump relay fails. It is not needed unless there is a problem.

The ECM turns on the fuel pump relay (and therefore the fuel pump) for 2 seconds at key on to prime the fuel rails for starting. It then turns off the fuel pump so that it doesn't run continuously if the ignition is turned on but the engine is not started.

The ECM also turns on the fuel pump when it receives DRPs (Distributor Reference Pulses) from the ignition module inside the distributor. The ignition module puts out DRPs any time the engine is rotating, which includes cranking or running.

You need power on the distributor to run the ignition module. That comes from the pink wire attached to the BATT terminal. That wire has 12 volts on it when the ignition switch is on.

ishootstuff

I see I didn't mention in this thread that I did not realize there was a separate wire to supply power to the coil. The pink wire that Cliff Harris mentioned was snuggled down where I couldn't see it. Duh... Anyway, no spark resolved. Too bad the damn thing won't run still. Getting WAY too much fuel.

hooked073

if you are getting way to much fuel check wires, connections at temp sensor and even the temp sensor itself. This controlls the amount of fuel needed by the temp of the engine so if it is 100deg out and you temp sensor is reading 30deg you are going to be dumping a lot of fuel and most likely wont start

ishootstuff

Thanks for the reply. I'm obviously new to this EFI system.

First off, I assume you are referring to the sensor just below the throttle body, right? Second, would that still be relevant if the cold start injector is unplugged? I have tried with and without the cold start injector plugged in. No difference.

I have pressurized the rail with the injectors out of the intake and they are not leaking. After the key is off, fuel pressure slowly drops to about 20PSI over a minute or so. I know that's not ideal, but shouldn't contribute to fuel soaked plugs.

Also, the computer does not throw any codes, though it's not surprising since it won't run.

I'm thinking of swapping the injectors out of my EFI converted 72 convertible Mustang, but that's a lot of work I don't want to do! I assume the L98 has high impedance injectors, but I haven't measured yet.

ishootstuff

I'm stumped here people. I can't get this thing to run. Plugs are all sooty. I did figure out the fuel pressure regulator is bad. It won't hold vacuum and fuel pressure goes as high as 60. I have remedied that for testing by hooking up an A/C vacuum pump to the regulator while I try to start it and it brings the pressure down to 38-42.

I have spark, I have injector pulse, timing is at 6° BTDC (although I have no idea where the plug I need to disconnect or whatever is), there are no vacuum leaks, firing order is correct. Injectors seem to be OK - they don't leak and spray the same looking pattern as other early injectors.

From what I have read, there is no way to test the MAF?

xrav22

The distributer advance is a single brownish wire with a black stripe(not shown) right around the wiper motor area. You probably need to time it with the advance unplugged. I saved this pic for the removal of my dizzy.

ishootstuff

Thank you. I found the advance goodie. Timing is 8° with it unplugged. My plugs are totally fouled and no longer sparking from trying so many times. Will clean/replace and try again.

Cruizin

This does not sound right.

If you are saying your timing only changed 2* (from 6* to 8*) between having the EST connected and disconnected your Electronic Spark Control module may be faulty. Setting the timing at 6* BTDC with EST disconnected (as you should) should result in about 18*-22* BTDC with the EST connected. While cranking with the EST connected your timing mark as seen with your timing light should have moved right up around the top of the balancer almost out of sight.

I'm not sure if checking the timing while the engine is only cranking (as apposed to idling) would only advance 2* but I believe the ESC module should be trying to advance the timing from the moment the engine cranks. The engine will only ever run at a true 6* to 8* when its at wide open throttle - hardly ever start from scratch at this setting as its way too retarded.

Also make sure you are timing of #1 cylinder (drivers side front).

If you are not getting enough advance you will certainly have starting issues.

ishootstuff

Thanks for the response, but what you are saying is completely opposite of how I understand ignition timing and advance curves. Regardless of computer controlled advance, or weights and springs in the distributor, the timing advances as RPMs increase, so even if the ESC module is not advancing the timing, it shouldn't prevent it from starting.

Are you saying that if you shoot your car with the plug connected, it idles at 18°-22°? That doesn't sound right to me.

Cruizin

I think you'll find 18* to 20* advance at idle is about right. Much the same when you put a timing light on a vacuum advance distributor with the vacuum still connected. High idle vacuum advances the timing. On the L98 this is now being done by the ESC module (no vacuum advance).

Cruizin

"The engine will only ever run at a true 6* to 8* when its at wide open throttle - hardly ever start from scratch at this setting as its way too retarded."

I got that wrong - The engine should start with the EST disconnected as its the normal way to set the timing. Once its set you stop the engine, disconnect the battery to remove the code 42 (ESC fault), plug the EST back in and you're done.

Just not sure what the ESC does to the timing advance while only cranking? Perhaps a small shift from 6* BTDC to 8* is correct? It will certainly advance it to where the timing mark moves right up under the water pump when idling (18* - 20*).

Either way your engine should still start if you have timed it to 6* BTDC with EST disconnected.

Cliff Harris

ESC is Electronic Spark Control -- that's the knock module. It sends a knock signal to the ECM if it detects knocks. Its only relationship to timing is that the ECM will retard the timing if it sees knock signals.

EST is Electronic Spark Timing. With the EST connector disconnected the timing is controlled by the ignition module inside the distributor. At idle the timing from the ignition module is zero degrees. You set the timing to 6° by moving the distributor -- that's known as the BASE timing or (sometimes) MECHANICAL timing because it's dependent on the physical position of the distributor.

When the EST connector is plugged in the timing is controlled by the ECM. It adds timing to the base timing to arrive at the TOTAL timing. At idle it should be around 20° (it is in my car but varies by year). The MAXIMUM timing also varies by year to around 40°. In my car it's limited to 42°.

Be aware that if the outer ring of your harmonic balancer has slipped then your timing can be WAY off. That has happened to me on two different Corvettes.

Cruizin

Yes, I stand corrected. My references to ESC should have read ECM. Too many 'E something' abbreviations and long work days.

Are you aware if the ECM advances the spark while cranking or waits until engine has fired and is running? i.e where should the timing mark appear on the balancer when engine is only cranking with EST connected?

ishootstuff

That's great information that I'm sure I'll use if I can get this thing running. I must have messed up the injectors or MAF at some point. I got it to run for about 3 seconds or so yesterday without touching the throttle, so I'm confident ignition timing is not an issue.

What I am unsure of, is the role of the MAF in this car. In some of my other MAF based cars, the car would start fine if the MAF failed, but run poorly and only up to around 2000 RPM. Is the same true for the TPI system?