my cars an 88 2.8 mpfi. basically it will flash the check engine light randomly. doesnt matter if its hot or cold, under acceleration or idling. but when the light flashes the engine will studder like its about to stall but then pick back up again with a high idle and run fine until the light blinks again.

when the issue first showed up the car would crank over but would fire up. my initial reaction was that the fuel pump went. mostly because i couldnt hear it priming and nothing was coming out from the fuel rail valve. this was about a week ago. since then ive been coming home from work and starting it. sometimes itll start right up and others it just wont. im still baffled at this situation and i still have a feeling this whole issue has something to do with this problem.

i replaced the maf and tps this morning. its running alot better and i havent had the no start issue for about 3 days now. the fuel pump will always prime up and stay running. when i took it for a drive the engine light will still randomly come on and studder the engine alittle bit. i want to check to see if the power is randomly cutting out to the pump. in the back of my mind i think it could be this but then if it was what is causing it?

i did alittle research about the cps causing the pump not to fire up because the ecm stays stuck in diagnostic mode. but thats all i could find. when i run codes the light randomly blinks and i cannot for the life of me figure out what codes its trying to throw. it literally goes nuts like its blinking nonsense. im about to go outside and check for codes again.

any help would be appreciated. ive been going nuts for a week and a half now.

 

well the fp is getting a constant supply of power. so there goes my theory.

 

I've taken a bit of video this afternoon on the way to autozone. I picked up a fuel filter. Also got a set of plugs and wires today.


Hopefully someone out there can give me a start.

 

Just got done switching the plugs out. The wires they gave me were wrong. Gotta wait till tomaro to get the right ones. The new plugs made no difference to the situation. They needed to be changed though.


I'm thinking tomaro I'm gonna pick up a cap and rotor as well.

 

The CEL is flashing or just coming on momentarily? The CEL is trying to tell you something. Try reading codes by turning the key off, shorting pins A&B of the ALDL(12 pin connector under the dash). PIns A&B are the top row, right hand end. Then turn the key on and count CEL flashes. long flashes are tens, short flashes are ones. Code 12 will always flash telling you that the diagnostic system is working. Then, if there are any other codes stored, they will flash three times each.

 

It just kinda randomly turns on and off.

See if you can make heads or tails of what its telling me cuz I can't. It just looks like its flashing nonsense to me

 

It looks to me that the ECM needs to be replaced... The timing between the flashes is all wrong. Not only that, but the flash timing varies, and the codes are almost intelligible (if they're codes and not random flashes without the ALDL set to display codes). If the ECM is doing that and the ALDL doesn't have the wire in it between A and B, then there is a problem either with the diagnostic circuit being shorted or the ECM itself.

And those plugs are fine... No need to replace them. Just make sure that the threads are clean as well as the tip where the wire connects.

 

As hesitant as I generally am about condemning an ECM, I may have to agree with Maverick. The code flashes, if the ECM is actually flashing codes at all, are too random to make out. I think I may have picked up a code 42 and possibly a code 23 but can't be sure.

At this point I would connect a compatible scan tool to be sure that the ECM even communicates and if there are in fact codes stored. I have had ECMs in early Ford EEC IIIs that did this same thing where they wouldn't clearly flash codes. I was able to read codes using a scan tool and repair the vehicle in each case. These ECMs functioned okay otherwise and were kept in service.

In your case, the random flashing of the CEL while the vehicle is running, not in diag mode, tells me that there is either a shorted harness or the ECM is internally shorted. That and the unintelligible code flashes have me leaning towards replacing the ECM.

 

so i picked up an ecm this morning. long story short. the new ecm hasnt made a difference in what the engine is doing. if i run a diagnostic test it cleary is just flashing code 12 at me. i took it for a drive and still just 12.

then i noticed something odd. there was this loud clicking noise coming from under the dash while in diagnotic mode. and whenever it clicked the engine light would hesitate alittle bit. sometimes code 12 would look like 2 long flashes or it would look like a few short ones. but when it didnt randomly click the light would keep flashing 12 normally.

i look under the hood and the maf relay is whats doing the clicking. during diagnostic mode is this relay supposed to click on and off or stay on? or just stay off?

 

The MAF relay is activated when the key is in run or start. It should not be clicking on and off at all. This makes me think that there is a poor ground or power connection in that circuit. First check for good contact at the "gages" fuse it is this fuse that the power to activate the MAF relay comes from. This would explain the odd flashes of the CEL and the engine cutout. If the fuse looks okay, then you'll want to check for good contact at G118(ground connection). Some data isn't showing me where G118 is and my GM electronic diag manual is at home.

 

From what I've read, during diagnostic mode, the ECM energizes all the emissions control relays. So the clicking is probably normal.

 

the clicking is completely random though. and it actually is making my other lights dim out.


is this fuse on the fuse block or somewhere else? on the block i have a "gauges" slot but not "gages"

 

nevermind. i went outside and ran a test again to keep the relay clicking and in the middle of trying to find what circuit was causing it the test just stops. i turned the key on then off to maybe restart it but it wouldnt do anything. the gauges just read voltage and the rpms just go in the negative.

i removed the clip and tried starting the car but it wont start. just cranks over. the pump wont even prime. turning the key to on is just silent.

this is pissing me off. something messed up is causing this crap and im pissed i cant find it.

 

It's the "gauges" fuse. As I said before, the ECM does not control the MAF relay. It is turned on whenever the key is in run or start. The relay is powered through the gauges fuse from the ignition switch and grounded at G118. I will try to remember to look up G118 tonight at home but I'm betting your whole problem is related to the "gauges" fuse. Excuse me for having the spelling wrong.

 

G118 is the ground on the back of the passenger's side cylinder head... Check to make sure it's clean, tight, and doesn't have any broken wiring on it. There should be a couple of wires there and also the body-to-engine ground strap. G118 is one of 2 major engine harness grounds (the other is on the other cylinder head, also in the back) and can screw up a lot of things if it's not secure and clean.

I wonder why they spelled the GAGES fuse different in the Camaro fuse panel?

Does the SES light come on now with the engine not running and the key on?

 

Thanks Maveric for that info on G118. I just looked it up in my Electronic Diag Manual. That ground being loose would definitely cause your symptoms. Just like a poor connection at the gauges fuse would. As Maveric also mentioned, GM commonly used the term gages. I guess maybe someone there don't spell so good.

 

Both the ground strap and that ground you described look pretty tight. I took the firewall screws off and tightened them back down again.

I was outside and dropped the fuse panel to check wires behind it. I didn't get anywhere but during checking I let diagnostic mode run and man everything was going completely nuts. The cel wouldn't blink any sense and the fuel pump kept priming on and off. Sometimes so quickly that it would just stay on. Plus a few relays, mainly the relay to the far drivers side on the firewall kept clicking on and off with everything else. Either the fuse box itself is messed up or a wire that I was being pulled while I fondled the box was causing it. I tried using a test light to see what circuit it was but couldn't find anything out of the ordinary from the fuse panel.

 

You guys got a diagram or info on the grounds under the dash? I'm about to remove my seat and go shoulder deep under there

 

Take the 2 screws out of the ECM bracket and drop that... Then examine the wiring.

Everything in the dash passes through to the engine harness and grounds at the engine EXCEPT for one little ground under the center console, right behind the shifter. The fuse panel has nothing to do with the fuel pump relay.

If everything else seems good, tight, clean, and otherwise unmolested, then the next step would be to try a replacement ECM. Especially since you now have more than one relay going bonkers and the only link between them is the ECM (since the ground has apparently already been ruled out).

Did you take apart the G118 and make sure the terminals are clean, or did you just look at it? You need to make sure that the connection on the cylinder head is clean as well as the body. The body grounds TO the engine, not the engine to the body. The engine grounds to the battery via the negative battery cable.

 

Isn't this already a replacement ECM? And the original did the very same thing. I think we are overlooking something here. The OP said that the MAF relay was clicking on and off. The MAF relay isn't controlled by the ECM. That's why I had him focus on the GAGES fuse and G118. If no trouble was found at either of these then we need to move on, but not necessarily to the ECM. The power to activate the MAF relay goes from the GAGES fuse to the relay through C100, which is the main bulkhead connector. There could be a problem there.

Do you have a DVOM? You may need one for this job. I would like you to focus on just one relay, since the MAF relay was the first one you noticed clicking on and off, I recommend you start there. Back probe the activation circuit and look for the power dropping in and out. Then trace that circuit back to
where the power loss is.

One thing that may be causing the ECM to flip out, aside from a bad ground connection, is the FP/ ECM in line fuse that is next to the battery. It's a 20 amp fuse housed in a black plastic cover that should be attached to the inner fender.

 

Um, he hasn't mentioned anywhere that's he's replaced the ECM...
MAF, TPS, fuel filter, wireset, plugs. No ECM.

And the fuel pump relay DOES NOT go through the C100. Not until 1990 (this is an 88). Everything for the fuel pump relay AND the GAGES fuse BOTH go through the C207, under the passenger's side of the dash. Not C100.

Fuel pump signal goes through C207 D, ECM IGN fuse through F, GAGES through G.

Probably want to check the C207 for an intermittent connection before replacing the ECM.

G118 is good. GAGES fuse is good. Fuel pump has no issues other than the flicking of the relay, so the power supply seems good. Although, there is a big splice in the main harness near the part where the harness splits off to go to the inline fuses and the junction block. I know I had to repair mine before I put the harness back into the car.

 

I did replace the ecm but got the same result. If I had a diagram of what you guys were talking about I could try to figure out where its all going. Sounds like you guys are giving me good info though.

All I got is a test light. The light only turns on when there's 6-12v present.

 

I dunno if it matters but if I remove the gauges fuse the engine light shuts off but the maf relay and fuel pump still goes nuts. The only fuse that actually stops everything is labeled 'engine control'.

Another thing. Its kinda small but if I wiggle the key in the ignition the door buzzer goes nuts also.

I tried checking wires around the steering column. The activity seems to rise when I mess with stuff around there. Also if I move the fuse panel around. The whole thing stopped again after about 15 min and wouldn't turn back on. Does the ecm shut everything down if you leave the key in the on position too long?

 

Wiggling the key and having the buzzer go on off is normal. Mine does that too and has for a long time.

 

The ECM doesn't shut things down if you leave the key on. These early systems aren't that smart. You lost power somewhere. Did you check the fuse by the battery? Sometimes it gets taken off the inner fender and you have top look for it. It's only about 1ft of wire away from the battery. Maverick mentioned taking the ECM bracket down and checking connections. At this point you shouldn't overlook any possibility.

What you've been doing around the column and at the fuse panel is called a wiggle test. I use this test all the time on intermittent electrical issues. Try to narrow it down to a particular area and look carefully at all connections for one being loose. Since the issue seems to be somewhere around the column, take a look at the wiring to the ignition switch. The actual switch is on the top of the column about 1ft down from the cylinder.

 

I dunno guys I'm completely dumbfounded. I can't seem to find exactly where the short is just wiggling stuff. My test light just shows everything either hot or no power. I can't find the wire that would blink it anywhere. I'm almost thinking about running a hotwire from the battery to the ecm power or the fuse panel.

 

A test light is a useful but limited diagnostic tool. For this level of diag you really need a good DVOM(10 megaohms per volt) and back probes or piercing probes to create solid connections at the wires you're testing. I'll bet you can pick up a good DVOM on Amazon for cheap. Look for Fluke brand. They are generally very good. Fluke also makes the best peircing probes I've found.

Do you have a service manual for this car? You need to have good wiring diagrams so that you can create a practical strategy for testing and not just run in circles. Have you looked at C100 yet? How about the ignition switch? You need an 8mm socket to loosen the fixing screw that holds C100 together, Then you can pull it apart and check the terminals for any sign of burning or corrosion. The ignition switch takes plug in connectors with latches that you squeeze and pull. Burned connections at the IGN switch aren't uncommon.

One thing about wiggle testing is that you have to be sure that the issue is actually responding to the wiggling of the harness and that the pattern you see isn't just there regardless of what you do. Try to zero in on the problem by checking all the plug in connections in the area where the problem seems to be. Electrical diagnosis can be frustrating. The better understanding you have of electricity and circuitry, and the system your testing, the the less frustrating it is. A really clear and thorough diagram, especially one that's printed in color, is very helpful.

I think what I would do with this car is start at the power source for the GAGES fuse, the activation circuits of the relays in question, and the ECM. Make sure that the on/off you're seeing isn't from the source. Then work you way towards the load, or where you're seeing the on/off behavior. Check each connection along the way. With back probes or peircing probes you can check connections by attaching on each side of the connection and testing with the DVOM in volts function and look for a voltage reading, especially voltage that fluctuates like the flashing and clicking relays. This test is called a volt drop test. Since any connection in a circuit is just a continuation of the current path, there should be nearly zero voltage across the connector. Any voltage reading that you get in this test is voltage drop and indicates a poor connection.

 

As far as the electrical problems, good luck. I know very little about electrical problems, and try to avoid them, if I can.


Code 12 is the Distributor reference pulse. Code 12 will flash every time you scan, while the key is "ON" and the engine is not running.

Possible causes of your flashing CEL, well you could have a short in the light itself. You will also want to check the distributor. If it is stock, replce the entire distributor.

Distributors were a problem item, on V6 thirdgens. Aside from the reluctor coil cracking and causing misfire, the o-rings go bad and cause oil to leak onto the starter. A defective ICM can cause the CEL to flicker like that. You will get a new ICM, already installed, with your replacement distributor. Check the brown wire, for setting your ignition timing, too.

 

Sorry to leave you guys in the dark so long. I let a local shop take the car Friday. I don't have the right tools or knowledge to figure out electrical issues. And this is my only car. And with my wife no longer having a running vehicle I was desperate.

Basically they found the main power supply from the fuse box to the ecm was frayed underneath the dashboard. Cutting the power randomly. All they did was run a new one with an inline fuse. Funny how I was just about to do the same thing. Except I paid them 400 bucks to do it.

 

Yeah. I'm one of the people you bring problems like that to, and I get paid very well to diagnose and repair these issues. If you had a DVOM and could do voltage, and especially a voltage drop test, you would have found the problem. Hopefully they did a good repair so that you won't have problems later on.

 

well the car starts and runs fine. No more engine light. But I'm afraid my electrical issues aren't over.

I tried installing electric seats today and everything went fine. I ran a spade into the port on the fuse box labeled IGN. it was hot when the car acc was on but turned off when the car was shut off. It worked fine until I started the car and took off. When I tried to adjust the seat the gauges fuse blew and the car stalled. So I moved the power wire for the seat to the BATT port. Car didn't shut off but it blew the fuse labeled ACC and the alt wouldn't charge the battery. Car ran terrible also on top of my parking lights and brake lights staying on even without the pedal down or the lights on.

after replacing the blown fuse the car ran fine again. Except now my parking lights come on with my brake lights so every time I press the brake pedal I get my brake lights in back come on and my parking lights up front.

 

Remove the power seat and go through the harness.

FYI, the power seat harness doesn't connect directly to the fuse panel... It goes to the junction block behind the driver's kick panel. Not that it makes any difference where the ACC fuse is concerned, but...

Going to want to drop the fuse panel again... May have melted a wire. Or, in your case, another wire.

 

I'm guessing it doesn't have a security system? If it did have a security that will cause the car not to run, normally the key, look into it if you have one, if not, prolly bad grown or shorted wire.

 

he shouldn't have a vats systems as they weren't installed until 89...I think it might just be the maf....a lot of times when they go out they start doing all kinds of stupid stuff....half the time you don't even get code because it's still sending something whether it's right or wrong...I would disconnect the maf and see if it runs fine (no stutter and so forth) the CEL will be on obviously but if it all stops then it's a huge possibility that it's your culprit


Nevermind this post...just saw he already got it fixed! what happens when I'm late to the party lol