Tune up issues on a domestic (I did something stupid).

[Zeke]

I've been chasing a miss in this '90 Cadillac I got when my mother died 4 years ago. I've spent a ton of time of this thing and had it running real sweet.

The miss came back and I've replaced fuel injectors and all kinds of things as per normal procedures. It did run nice when cold, but started acting up when it got hot. I began to suspect the plug wires and was unplugging them one at a time looking for the dead cylinder (rubber gloves and insulated pliers). The spark was jumping toward the coil pack and the car died. So, I burned what up? The pick up, the rotor? How do I test this stuff?

Edit: Coil tested good, module didn't, replaced module and still no spark anywhere. Pick up coil tests good. Hal effect sensor tests good. I did check the fuses since I had a bad experience there on another car (long story, short lesson). I do have power to the coil, etc. The problem is upstream and in the dizzy, there is no spark yet.

I have replaced the coil and retested the new coil. I've gone thru a few boxes of new coils and they all test the same. Not what the Internet says is right and that's really confusing. My coil(s) show .5 Ohms across the primarys and infinite from the + and - leads to the secondary with the resistor button removed.

[red-beard]

Donate to Father Joe

[Kevin Taylor]

Drop a 944 Turbo engine in it. That outa keep you busy.

K.T.
1973 911 E 2.4 MFI
1983 911 SC
1978 911 SC
1965 Devin "D" - 1967 912 Power Plant

[fingpilot]

Most CDI ignition coils do not like firing without a load on them. Usually toast in a sec or two. See if McParts has the coil (might be more than one coil there too), or someone that can test the one you have. If the coil is good, then the CDI box itself went. probably a junkyard part for that one.

[fingpilot]

Sorry Milt, neighbor had one of those 4-6-8 vario things in a 90's Caddy. It did not have the usual GM HEI, but a CDI thing with multiple coils. Was my only reference point.

You could just drop a 944 Turbo engine in it and be done with the headache.

[Kevin Taylor]

Be creative and make it work. Engineer some mods.
944 Turbo Caddy...........now that would be smooth ride and styling.
Chicks would dig it. You could get a big gold chain necklace with a
Porsche emblem on it. BBS wheels?

K.T.
1973 911 E 2.4 MFI
1983 911 SC
1978 911 SC
1965 Devin "D" - 1967 912 Power Plant

[mb911]

sticking valve? Check compression? When it warms up it dies? or just runs poorly? could it have something to do with IAC valve? Warm up enrichment? Head gaskets? Is the 3.8 famous gm motor?

[mb911]

sorry can;t be much help. I just went through something similar with my 98 for SUV with a 5.4 it has COP . I became an expert in engine diagnositc and also engine removal over the past six weeks. boy it was fun but now 2000 later and 40 hours of my time it runs like a champ until next time. the good news is it gets much better fuel milage then before almost double. but not to steel you thread.

This is what i would do. first do basics compression test,timing, etc. then check for vacum leaks. anything with emmsion controls lives or dies from vacum leaks. next verify your ignition theory . I guess it is possible to be a problem. my boat ate the dizzy gear but started running rough and got progressivly worse.

[masraum]

If it's an old GM with HEI, then you may be able to replace the HEI control module that might be pretty cheap. They fry easy and that may have been where the original miss was coming from. The control module should take about 10-15 mins to replace, is under the rotor, and kills the engine when it fails.

I went to the Autozone website and checked a '90 deville. It uses a very, very common control module. $22.

[john70t]

Definitly an ignition-something problem, usually it's the module which goes first. The new electronic cars don't like the old-school "pull-plugs rpm-drop" trick.

FYI:The ig module replaces the points, and acts as a "middleman" to selectively ground the coil.
-After it gets a pulsed signal from the pick-up on the distributor (or crankshaft), it opens the ground path running from the coil's primary windings(many small wires around the outside). This collapses the primary winding's magnetic field into the secondary windings(fewer thicker wires around a magnetic core inside), and fires high voltage out the coil wire.

An old coil may test correctly for resistance(through the primary circuit), but under a real load it will short through the housing and not spark. This is because the DVOM only uses low voltage to check the resistance, and that isn't enough to jump through a partially-burned wire wrap.

Check first that the coil is getting the 12V from the ignition circuit, and the ig module is getting pulses(AC?) from the timing pickup when cranking(probably uses a 12V supply as well)-They need these to work.
I'll guess a bad distributor pick-up, a bad dizzy/rotor or a bad coil wire.

[john70t]

http://en.wikipedia.org/wiki/Ignition_system

[lm6y]

Milt, replace the hall effect pickup coil. The heat of the engine bakes the wires, and the wires become brittle, and break right where the pigtail enters the pickup coil body. the added resistance in the wire often eats ignition modules. At best this causes an intermittant ignition problem, at worst, it shuts the whole thing down. These used to be sold by the color of the lead wires for the right one.

You have to remove the distributor, remove the roll pin that holds the drive gear on, and then disassemble the distributor to get to it. Just put it back together the way it came apart (pay special attention to the washers under the drive gear as this sets the gear mesh between the cam gear, and the drive gear on the distributor).

I assume you know how to take it out, and re-time it once it goes back in.

How does the carbon button, and spring look under the coil?

If the coil is good, gets power, a good ground, the module is good, the pickup coil is about the only thing left.

Hope it helps!

[Seahawk]

Milt,

I've been following this thread and feel your pain. At the risk of getting hammered, have you checked fuses and grounds? Have you done the "fuel pump" spew? Fuel pumps and filters suck when they should blow

Quick sea story: Stuck at Luke AFB in the mid 80's. My Sun-Strand Aux Power Unit wouldn't start. Without the APU, you can't start the big jets on the H-60.
We pumped the tank that proviides initial juice to turn the APU to start speed at least 10 times in the Az heat...we were all pissed.

We call it a day. Since I am the Aircraft Commander, I begin to put all the charts and maps in my nav bag. My IFR supp was covering the APU circuit breaker, which was popped

Reset said CB, APU fires up and we're on our way.

I took my co-pilot and crew chief to dinner when we got back to San Diego. It sucked to be me

[john70t]

Proof is in the puddin'.
Disconnect the fuel electrics(flooding) and the coils 12v supply(prevent another short) and see if it's sending pulses to the coil when cranking. Everything up to the coil will be good then.

Shoot, mabye it's random like wiping out the fuel pump relay or the distributor isn't grounded.

[john70t]

Ha! Just tried to do a Google search for "1990 Cadillac wiring diagram" and the first 25 pages were trash all from: "****.computeritc.net"
I guess that was a Google-bomb(?)

The Hall-effects sounds like the last variable to replace Milt, but it sounds like the yellow wire would be the signal.

[lm6y]

Milt, I've seen bad hall effect sensors test fine with an ohm meter, but not run the car.

The resistor of some sort, should be a capacitor, or some times called a condensor. Never seen one cause a problem on a HEI .

I can't find an old one around to test, but I "think" the red is hot to the low voltage side, yellow is the ground to the low voltage side, black is the ground to the high voltage side, and the button on the bottom is the positive for the high voltage side.

[Zeke]

Originally posted by lm6y
Milt, I've seen bad hall effect sensors test fine with an ohm meter, but not run the car.

The resistor of some sort, should be a capacitor, or some times called a condensor. Never seen one cause a problem on a HEI .

I can't find an old one around to test, but I "think" the red is hot to the low voltage side, yellow is the ground to the low voltage side, black is the ground to the high voltage side, and the button on the bottom is the positive for the high voltage side.

From the 911 board:

Originally posted by 911pcars
Hint for backyard DIYers.

When performing upgrades and modifications, start and complete one item at a time (if possible), then verify things still work as normal. Proceed to the next phase.

This procedure minimizes having to diagnose two or more systems that could have contributed to a no-start, no-idle, no-go situation.

This also minimizes the next backyard DIY strategy - buy new parts as a diagnosis tool. The thinking is that buying and installing new parts automatically replaces the malfunctioning part which is tossed along with working parts. This strategy also ensures that after about 10 years, nearly every part in the car will be no older than 10 years old.

Sherwood

This is what I'm trying to NOT do.

I've narrowed it down to, as you say, two things that test OK but perhaps aren't, i.e. the Hall effect sensor and the pick up coil. It's either there or I fried the ECM. Now, there is a mode in which the module runs the ignition on EST (electronic spark control) bypass. If I can make the car think it's in that mode, it might run in spite of a bad ECM. At least then I'd know to head for the salvage yard for a used ECM. Right now, I'd just like to find the problem.

BTW, I've been over the grounds and other leads for continuity. So far, so good, but no spark anywhere.

[unclebilly]

I had a similar problem with a GM V6 in an S10. I changed out the module in the dist to no avail. The problem was the 'computerized spark control' - I changed everything over to a vaccum advance setup and it was ok. This probably isn't an option for your caddy.

[unclebilly]

Oh yah, GM also uses an ignition module on their newish stuff. The one in my 89 1/2 ton quit one night on the way home from hockey. It is a cheap part and I now carry a spare.

This same thing happened to a guy on one of the hockey teams I play against a week later - he was amazed when I pulled out the spare and installed it in his truck and it fired right up.

My guess is that this is your problem.

Oops - I see you changed the module and it still runs, just misses.

I second Ben's comments about a burnt or stuck valve. Have you got spark at all 8 leads? Have you done a compression test? Is there an injector not firing?

[911pcars]

Hi Milt,
I know the feeling and empathize with you. I'm trying to create a basic digital electronic circuit and I'm acting like a newby.

Unfortunately, I'm not conversant in HEI. As a matter of fact, if my Crane box died, I wouldn't know what to do either except to replace it (assuming I knew for sure that was it).

There are DIY books on HEI ignition systems that might be of help. Autobooks in Burbank (a ways from LB) would have them.

Sherwood