Hello! Trying here for help as I've run into something that is a little out of my comfort zone for diagnosing. Last time I tried running it there was a very scary sounding backfire so I'd like some advice before getting back to it.
I have an '86 GT and one morning it suddenly would not start. I checked fuel pressure and spark, they are fine. Timing was at 10 degrees based on timing mark. I don't think the balancer has spun based off checking TDC with a screwdriver but I can't be 100% sure because I wasn't measuring that precisely. It will start with some throttle, but runs rougher than it ever has before and backfires dramatically.
I'm not a professional mechanic and just have a little experience with my own vehicles, so I'm feeling a lot of uncertainty trying to figure out what might be happening and what I need to do to fix it. Could it be fuel injectors? Cold start injector maybe? I bought new injectors so I may just go ahead with switching those, but it would be nice to know if that has a chance of fixing this or if there's something else I need to look at. I live in Florida so I am also considering deleting the cold start injector. If the CSI was leaking would could that cause this? Does that make sense that it would need the throttle open a bit to start with a leaking injector? Or could this be something else?
I have an '86 GT and one morning it suddenly would not start. I checked fuel pressure and spark, they are fine. Timing was at 10 degrees based on timing mark. I don't think the balancer has spun based off checking TDC with a screwdriver but I can't be 100% sure because I wasn't measuring that precisely. It will start with some throttle, but runs rougher than it ever has before and backfires dramatically.
What does "fine" mean? Keep in mind we have no idea of your ability to determine what is or isn't "fine". What is the fuel pressure while the engine is running? How quickly does the fuel pressure drop when the engine is turned off? Does the spark snap across a 1/4" gap to ground? Was the ALDL jumper in place when the ignition timing was set?
The ignition control module is a common failure point, but sometimes the issue is simply corroded connections from the pickup coil and/or the ignition coil to the ICM.
The issue could also be something as simple as a fouled spark plug.
Another simple thing to check is to make sure both injector fuses are good.
[This message has been edited by Patrick (edited 02-11-2024).]
What does "fine" mean? Keep in mind we have no idea of your ability to determine what is or isn't "fine". What is the fuel pressure while the engine is running? How quickly does the fuel pressure drop when the engine is turned off? Does the spark snap across a 1/4" gap to ground? Was the ALDL jumper in place when the ignition timing was set?
Thank you Patrick, you're right I could have checked those better. I just figured I knew it had some fuel and some spark. I did not check fuel pressure while running because I was too sketched out by the backfires once I got it going, but it was 45 psi with ignition on and held there after I turned it off. The jumper was in place when I set timing. I will check spark with a 1/4" gap tomorrow, along with the injector fuses and anything else you guys think I should look at. About a year ago I installed a new DELPHI ignition control module, NGK spark plugs gapped to 0.045, new spark plug wires and a Summit 40kv coil. I realize now it might have been better to use ACDELCO where I could. I doubt the spark plugs are fouled though because they are so new and the problem happened very suddenly, but maybe there was a sudden failure with those or something else in the ignition system. I have another ICM I could try.
This literally happened overnight, I had just got it running decently after sourcing a replacement vehicle speed sensor and letting it calibrate the idle air control valve again, which I think was the source of the problems that had originally led me to replacing all those ignition components. I drove it regularly for about a week until that morning when it wouldn't start.
Patrick's suggestions are good, especially the aldl jumper, another thing to maybe check with a voltmeter is the TPS sensor, when that goes bad, it can confuse the computer into giving the engine the wrong a/f ratio, especially when starting, as there's no vacuum readings. When my TPS sensor went bad, it ran very rough, jumpy idle around 2000+rpm, and if I got on the gas too fast, it would backfire. The TPS is something that can be good one day, and either completely or partially fail the next.
Also check for broken connectors in the engine compartment. The clips are frequently broken unless they've been replaced. Make sure they're all in good contact. There's a connector plugged into the ICM that pretty much refuses to stay in place if the clip is broken, and it can cause these symptoms when it gets flaky. There's also a short harness from the ignition coil to the ICM that is notorious for going bad due to heat exposure.
Listen for vacuum leaks - although on my car I've noticed the IAC is loud at cold start and sounds like a vacuum leak until it closes.
I think the CSI would have to be leaking pretty badly for it to cause these symptoms. But maybe it's been leaking before and this is just the point when it got bad enough to be noticeable. The CSI isn't critical, but I tried unplugging it on my car and it took a lot longer to start even in warm weather. Another source of unmetered fuel could be the fuel pressure regulator. It's possible for them to leak fuel into the vacuum hose that attaches from the regulator to the manifold. If you prime the fuel pump and then put suction on that hose, fuel should *not* come out.
Bad injectors are possible, but that would just be a guess. If one of the injectors have electrically shorted then it would disable the whole bank of 3, so then it would be running on 3 cylinders. It can run on 3 cyls with some throttle but I don't think it should backfire. A simpler cause of that scenario is a blown fuse as Patrick referred to.
Since the fuel pressure held when you shut the key off, it sounds like you do not have a leaking injector. I'm not sure if this rules out a leaking fuel pressure regulator though. Without the engine running there's no vacuum, so maybe then it wouldn't leak the same as when running.
It could be an ignition issue, or a bad sensor reading causing the ECM to call for way too much fuel, leading to enough unburned fuel in the exhaust that it backfires. Backfiring out the exhaust suggests it's either running rich or bad ignition, not lean. But any stored trouble codes could give more insight.
Before buying parts... Clean/fix all grounds & + wires in engine bay. Iffy wiring causes many problems. use silicon or permatex brake grease. See https://web.archive.org/web...ierocave/ecmwire.htm & rest of section.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Fuel injector fuses are not blown. Spark at 1/4 inch was bright blue for the most part, immediately after starting to crank I saw a little duller color but I could have grounded my wire better probably.
Checked TPS, I've got 0.35V closed and 4.56V at open throttle.
The clip on the connector from the ICM to the coil is broken, but it is fully seated and secured with Tesa 51036 tape which seems to hold it very well, I can't wiggle it at all without pulling that tape off. The only other broken clip I know about is the MAP sensor, but it's been staying put on its own so far. I will try to look at the other connectors.
I will try testing the fuel pressure regulator with suction. I have a new diaphragm as well as new injectors, but I wanted to figure out more about what is happening before I take that all apart. And I do not have a replacement for the CSI. I don't really know what a leaking/failed injector looks like, but the seals must be good because it's not dumping on the intake when pressurized. Was thinking they could fail internally and lose their metering ability, dumping too much fuel when activated. But thinking about it after learning more about them, the metering comes from the PWM signal. Could the injector actuators get sticky and stay open longer than they're supposed to?
When I bought it it had vacuum leaks, of course they affected the idle but nowhere near this much. It is scary to run it right now and hard to hear vacuum over the ridiculously rough idle, so I'm really hoping that isn't the problem.
When it was running well, it still used a lot more fuel than I believe it should have. Something like 10-15 mpg, and the exhaust smelled a bit like gas. Maybe the CSI was leaking that whole time and recently got worse? But if it is always open, how does it hold fuel pressure? I will pull a spark plug or two (maybe all three rear ones, hate reaching the front) and see if I can confirm if it's been running rich for some time.
I'm also not sure it backfired in the exhaust, I'm worried it might have been intake. I was standing beside the car when I heard a very loud bang from the engine compartment, not so much from the tailpipe. But an intake backfire is not possible unless the timing is way off right? I know the balancer can spin, but mine isn't loose enough to move by hand and it was working with the same timing for several months. Whatever is causing this is something that can happen suddenly overnight. It went from driving decently and had a normal idle when I parked it one evening, to suddenly and consistently behaving the way it is now the next morning. Checking all connections and grounds is a good idea and I definitely will do that as I work on the car more. I've checked and cleaned a lot of them but not everything. But though I could be wrong, I feel like bad connections would cause a more intermittent issue and not the night and day difference I'm experiencing here.
When it was running well, it still used a lot more fuel than I believe it should have. Something like 10-15 mpg, and the exhaust smelled a bit like gas. I will pull a spark plug or two (maybe all three rear ones, hate reaching the front) and see if I can confirm if it's been running rich for some time.
With those mileage figures, I wouldn't be surprised if your plugs (one or more) are all fouled due to an excessively rich mixture. How old is your O2 sensor?
If your O2 sensor is okay, I'd then suspect the Coolant Temperature Sensor and/or the Manifold Air Temperature sensor is telling your ECM that the temperature is -40°. This is where a scanner or software like WinALDL really comes in handy.
[This message has been edited by Patrick (edited 02-13-2024).]
I just pulled the spark plugs from cylinders 1, 3, and 5.Getting a bit fouled for sure, and 5 is much worse than the others. Image imbed didn't work but here's a link. The picture with flash makes it look a little cleaner than it does in person. image
Without a lot of frame of reference, it is still worse than I was expecting. Though I did make a lot of short trips in the time it was running. Would this level of fouling be an immediate issue? Can still see the white in the insulator tip so it's not completely coated. Could this cause a problem to show up as suddenly as it did?
As far as the sensors... well, I replaced all of those already. I know now it's kind of dumb to just throw parts at it and new stuff isn't guaranteed to be good. When I got it, it had a radiator leak so when I replaced the rad I also got a new coolant sensor and thermostat. I later replaced the O2 sensor and intake air temp sensor hoping they would help with the fuel economy, but they made no difference. The O2 sensor is Bosch, so I hope that's a good one. The other two were cheapo. Maybe one of those has failed.
I'm going to try to get WinALDL. I have no idea why I did this, but I pulled the instrument cluster out to replace bulbs and swap out one of the gauges after this happened without checking the codes. I have it back together now and will reinstall tomorrow and find out what is stored.
[This message has been edited by WingsGT (edited 02-13-2024).]
The Upload Media tab works fine. Just make sure you're logged in before trying to post.
Many people here will disagree with your choice of plugs. Supposedly they don't work well with the 2.8's factory ignition system. The advice often given is to use standard ACDelco (or NGK) plugs, and not those highfalutin ones with tiny electrodes.
Thanks Patrick. I had tried the image tags added with the button up top but alright, upload media next time.
I got these NGK before I knew much about the car and I had used them on previous vehicles. But from what I've read I'm convinced to get ACDelco next time. These seem like they might be okay for a little while more?
Could it be lean? I've always suspected the car was running rich. Replaced the fuel filter a while back as well. The one I took off looked pretty clean, maybe replaced not that long ago by the previous owner.
I got these NGK before I knew much about the car and I had used them on previous vehicles. But from what I've read I'm convinced to get ACDelco next time. These seem like they might be okay for a little while more?
I'm rather surprised that The Ogre (theogre) hasn't chimed in on this, but he's quite adamant that those plugs you're using will cause problems when installed in a Fiero 2.8 engine. I've never used them myself in a Fiero, so I can't confirm nor deny what he says about them.
Checked TPS, I've got 0.35V closed and 4.56V at open throttle.
Going off of memory, isn't the TPS supposed to be 0.2v closed about 5v open, the open doesn't seem to bad, maybe a little low, but .35v closed on mine was enough to cause done of the problems you describe, I got check engine light, and throttle response was horrible, if I gave it gas to quickly, then it would seem to backfire a bit out the intake, and smelled bad. If I drove it, I'm sure mpgs would have been bad, it had a high, unstable idle, and was really easy to stall.
Throw those plugs straight into the garbage and put standard Copper plugs in it, AC Delco preferable and start there.
Put a socket/ breaker bar on the harmonic balancer bolt and turn it back and forth and see how much free resistance (slop) there is before you feel the drag of the Camshaft / drivetrain. There should be very very little slop, anything more than just a hair you may have a worn timing chain and possible it jumped camshaft / valvetrain timing.
Fiero Pickup coils and ICM's generally either work or don't, but who knows.
Forget the TPS, The 2.8 injects fuel above the intake Valve where it pools ( when I say pools, I don't mean liquid gas, I mean the fuel/ air charge is there ready to go it} even under normal condition and does not get introduced to any combustion process until that intake valve opens. Ultimately The intake valve opening controls when the charge is is injected into the combustion chamber.
If it is backfiring continually as it's running, possibly it could be a burnt valve, that Spark plug pic does have a nasty gray color to it.
[This message has been edited by jelly2m8 (edited 02-16-2024).]
Throw those plugs straight into the garbage and put standard Copper plugs in it, AC Delco preferable and start there.
Put a socket/ breaker bar on the harmonic balancer bolt and turn it back and forth and see how much free resistance (slop) there is before you feel the drag of the Camshaft / drivetrain. There should be very very little slop, anything more than just a hair you may have a worn timing chain and possible it jumped camshaft / valvetrain timing.
This distance is 4 degrees right? Is that too much?
That is quite a bit of slop, and that's not even without any load on that timing chain in which it probably stretches more.
A quick test would be to add a few degrees of ignition timing and see if that makes any difference in starting and or roughness. This isn't a fix but may help diagnose or confirm a timing issue.
Higher mile 2.8's always ran better with 12 degrees ignition timing just for this reason.
[This message has been edited by jelly2m8 (edited 02-18-2024).]
I just found the ALDL connector I bought a while ago but never finished looking into WinALDL. Getting a little busier this week but I should be able to get that going in the next few days, and in the mean time I will be ordering the correct spark plugs. The instructions for the cable show it wired to a DB9 connector for RS-232 serial. I have an RS-232 to USB adapter and I saw some posts saying that should work, but is there anything tricky I might need to know to get it working right? If it's as simple as it looks that would be awesome but just in case you have any tips!
But I am worried about running it long enough to get a live readout or change timing. I know at some point I might have to start taking riskier troubleshooting steps, I just want to make sure it's as safe as possible. Maybe I should do a full compression test, but also if it's backfiring it seems like that might be conclusive enough that it would fail somewhere. Could I find valve damage from "just" taking the covers off? I've read that it's difficult with everything assembled. Some people saying they did it with the intake on and others saying they had to take the whole thing off, or just the upper plenum. I'm not super confident about maneuvering wrenches back there without clearing some space since I haven't done it before, and just changing the even number spark plugs is hard enough. Also not excited about trying to hook up the compression tester to those cylinders either but at some point I've got to get over that. If I was digging into it to check stuff, I would like to replace the fuel injectors and regulator while I'm there but I also don't want to introduce new problems while trying to find this one.
Engine has about 87,000 miles afaik. When I bought it the speed sensor was going out intermittently and then totally failed on the drive home. Amazing how that happens.
Would it be unreasonable to take the cylinder heads off and have them rebuilt, and replace the timing chain myself at this point? It doesn't seem like it would be a crazy amount of money since I found a place that said they could rebuild heads for $100 each, which I found kind of surprising considering other quotes I got in this area but I think they're legit. I really want to keep the cylinder heads in good condition for a 3.4L swap down the road. I've been trying to learn stuff gradually in the hopes I would be able to handle that swap comfortably by the time something major failed on the 2.8, but now here we are.
In regards to setting up a laptop to work with WinALDL... it's relatively simple, but... sometimes it's a little tricky to get anything to register on the laptop due to COM settings. Give it a whirl and if you have any trouble, yell here for some help.
[This message has been edited by Patrick (edited 02-19-2024).]
Would it be unreasonable to take the cylinder heads off and have them rebuilt, and replace the timing chain myself at this point? It doesn't seem like it would be a crazy amount of money since I found a place that said they could rebuild heads for $100 each, which I found kind of surprising considering other quotes I got in this area but I think they're legit. I really want to keep the cylinder heads in good condition for a 3.4L swap down the road. I've been trying to learn stuff gradually in the hopes I would be able to handle that swap comfortably by the time something major failed on the 2.8, but now here we are.
Wings GT... I'm going to have a set of 2.8-3.4 HO heads that have been completely rebuilt, which I will not need, and will not be using.
In short, I bought a 3.4 V6/60 long block, in which everything has been refreshed, and then I ordered a set of ported ARI Racing Heads w/ Swirl-port valves. So I won't need this extra set of heads (which are totally machined and fitted with new valves). Only thing, it's going to be a couple of months before I swap them out, but you can have them for free if you want them. I am also located in Florida...
[This message has been edited by 82-T/A [At Work] (edited 02-19-2024).]
Haha, I know Patrick. Not actually going to do all that right now. New plugs are on the way. Couldn't find the serial-USB converter I thought I had so I ordered a different one with flying leads and the chip in the USB side. I will continue with troubleshooting the parts I have, just sometimes starts to seem like I'm looking for issues that would be irrelevant after doing other things I might want to do in the future. But if it is something else I need to figure it out now.
Thanks 82-T/A, I appreciate that and it makes me feel better about blowing these up if it comes to that. Probably shouldn't be so precious about the 2.8 heads since anyone swapping anything other than the 3.4 would also be getting rid of them. Not to derail but what are you doing for the intake on your 3.4?
Gonna do the compression check soon, new plugs just got here.
Question on the WinALDL cable. I want to use 5v VCC from my USB adapter instead of the 12v battery or serial DTR pin like the diagrams on the website show. I've been trying to figure out if I should use a different resistor there, but now I'm thinking it's just a pull up resistor and I should stick with the 10kohm. That would be easier and in theory keep everything 5v on the serial converter side of the transistor, but is there any problem with doing it this way?
Will WinALDL be able to read sensor data with the key in accessory? We were talking about which sensors might have caused this by failing suddenly, and that's probably the only way to rule out the O2 sensor right? Does the ECM even use the O2 sensor before ignition? But otherwise, I checked the intake air temp sensor and it read normal at room temperature. Haven't checked the coolant temp sensor yet. Should I also check the cold start temp sensor? Or anything else?
[This message has been edited by WingsGT (edited 02-25-2024).]
I don't understand your questions about the cable.
quote
Originally posted by WingsGT:
Will WinALDL be able to read sensor data with the key in accessory?
You mean the key just turned to "RUN", without actually starting the engine? Some of the sensors will function.
quote
Originally posted by WingsGT:
...that's probably the only way to rule out the O2 sensor right? Does the ECM even use the O2 sensor before ignition?
You're not going to get any pertinent readings from the O2 sensor unless the engine is running. Same thing with the MAP sensor.
quote
Originally posted by WingsGT:
Should I also check the cold start temp sensor?
It's not a sensor, it's a temperature controlled switch. If you're concerned that it might always be "closed" (doubtful), just unplug the harness from it.
[This message has been edited by Patrick (edited 02-25-2024).]
Ok, just trying to rule out things out for sure where I can. So O2 sensor readings wouldn't affect starting. I've been looking for more info on the cold start injector and its switch, can't find what temperature it's supposed to switch at but it sounds like the injector is always active when cranking so the switch also would not affect starting.
I built the WinALDL cable the way I was describing and I'm getting some data through (with key on run) but it isn't populating into the sensor fields. Have you seen it do this before? I just have this on the RAW Data tab and nothing on Sensor Data. I'm thinking this at least means I got the wiring right because the data doesn't look completely random, but I'm not totally sure and it also could be a problem with the USB converter I'm using.
It's been so long since I've used the program, I'm afraid I can't be of much help. Make sure to use ALDLView though to see the info displayed in a manner that'll make some sense.
The first thing I like to check is that both the Manifold Air Temperature and Coolant Temperature sensors are working properly. After the car has sat all night, see what the readings are. You can plot multiple readings on the graph at once, and ALDLView will also save GIF's of what you're looking at.
Here's an old reading I just randomly grabbed of my Formula. Notice how when the engine starts, the two temperature readings are very close to each other.
Oh sweet, didn't know about that. Will definitely use that when I get some readable data.
I'll have to try some different things with the WinALDL cable, see if I can get a resistor across pins A and B for diagnostic mode. Found some other posts here that said that was the only way it worked. But the ALDL plug I have was made for something else and doesn't have a wire for pin B, so I'll have to figure that out.
I would suggest starting a list of what you've confirmed to be in working order. Follow it up by what you're observing.
Instant/overnight symptoms are rarely mechanical. Check for bad grounds/corroded electrical connections on the ignition system. Just as others have already stated.
I would suggest starting a list of what you've confirmed to be in working order. Follow it up by what you're observing.
Instant/overnight symptoms are rarely mechanical. Check for bad grounds/corroded electrical connections on the ignition system. Just as others have already stated.
Kind of have a list running but could probably organize it better. I need to check the grounds more thoroughly probably, so I'll work on that as well as doing the compression test I've been trying to get to. I've checked most of the electrical connectors that I can find easily, none of them ever looked that great but I used some contact cleaner on some of them a while back and I don't see any serious corrosion on anything now. But I can go back over everything again. Are there any connections I should look at that are more difficult to reach or locate?
Tested spark from the distributor and it seemed strong enough. Any way to test that more accurately? I also read ECM codes (blinking light) and it only had code 12. It sounds like that's normal when the engine isn't running and the ICM does actually work based on spark test, so if it is a bad connection somewhere else could it be something that doesn't store a code? I do hope you're right and it's not mechanical, but it seems like that also makes it harder to find. Still kind of worried it might have jumped timing, but I don't remember it running weird at all the night I parked it.
Bent over another pin in my ALDL connector so I think I can connect a resistor across pins A and B now (R3 in the instruction diagram), will try to get that put together and test WinALDL again tonight or tomorrow.
Spark at 1/4 inch was bright blue for the most part, immediately after starting to crank I saw a little duller color but I could have grounded my wire better probably.
quote
Originally posted by WingsGT:
Tested spark from the distributor and it seemed strong enough. Any way to test that more accurately?
I don't know what to tell you. It either jumps a quarter inch or it doesn't.
I don't know what to tell you. It either jumps a quarter inch or it doesn't.
Good enough for me then!
Tried the ALDL cable with a 10k resistor added between A and B for diagnostic mode, still didn't work. This time I'm only getting one packet of data instead of periodically getting 2 like my earlier screenshot showed (red box at the top, guess it's supposed to say 20 for 20 separate data packets). Not sure if that means anything. But the data did stop when I turned the car off, so it's probably not floating values from bad wiring inside my cable. Could still be a problem with how I wired it. I'll try adding external power from the car battery instead of using the USB 5v, and if that doesn't work maybe start over with a different serial converter.
But I have to go out of town for work tomorrow so that'll have to be this weekend.
