OK, first post so forgive me if I'm in the wrong topic area. Mods move at your pleasure.
I've been a design engineer for 40 years and I'm the guy that designed all the Fiero suspension arm dimensional gaging and tooling for Pontiac and Entech back in the day. Back when GM was throwing millions at stuff like that...private jets, topless restaurant dinners, gallons of booze...but, that's another tale for another day.
Anyway, in doing all that work on the Fiero project I got hooked. Actually, I was hooked when I saw the prototype Fiero's while touring the new 'Vette factory back in 1984. So I bought one. A brand new silver 1985 2.5, 5-speed. I loved it.
Then life changed. I eventually moved out to a farm and in 1999 drove my Fiero out to the new house we had just built and parked it in the garage. 27K miles on the clock. Looks like new. Underside is spotless. No rust anywhere and probably the best storage conditions this side of a heated, dehumidified room. Put a breathable car cover on it and life went flying by me. If you've done the math the thing sat without even so much as the doors being opened for 20 years.
Fast forward to last month when I decided it was time. Time to drive the old girl one more time before I end up in a hole in the ground. Parked it with a full tank of gas, of course (had it ready for a honeymoon, but ended up taking another car on that trip). Dropped the gas tank to find about an inch deep couple gallons of nasty, stinky stuff and proceeded to flush the tank out over and over and over. I then installed a new fuel pump and filter sock. Stuffed the tank back in place and test fired it up while still on jack stands with 5 gallons of fresh gas in the tank.
Success! Or so I thought. It ran fine that first time for maybe a minute or so as the memories flooded back to me, hunkered down in the sheepskin covered seat. But, the next day...hard starting...wouldn't idle...stalled repeatedly. The only way I could keep it running was by rapidly pumping the gas pedal. Crap! Tripped the code with a paper clip and got a 22.
Replaced the inline filter, the injector nozzle, the throttle position sensor. Only a little better. The more it warmed up, the more it wanted to die. Spray carb cleaner down the throttle body everywhere I could get it. No better.
I think I'll check the idle air valve next and replace the MAP sensor (will check for vacuum leak). I don't think it's the temp sensor telling it to go too rich or too lean, but I've been wrong twice before in replacing the TPS and the injector nozzle.
Doesn't smell rich. Can only hit about 3,500 RPM and once got it to 4,100 RPM. When engine starts slowing down it seems like it's not getting enough gas, if anything. No backfires or really noticeable timing burps. Once it 'catches' again the engine accelerates more or less normally and even stutters and picks back up fairly smoothly.
It has a hot spark, spark plugs look good.
Am I headed in the right direction or barking up the wrong tree? Any advice is appreciated.
My 86 2.5L was doing that and one of the 2 vacuum hoses coming off of the air filter was bad. It does sound like it may a vacuum issue. Only a suggestion.
Originally posted by CampyBob: I've been a design engineer for 40 years and I'm the guy that designed all the Fiero suspension arm dimensional gaging and tooling for Pontiac and Entech back in the day. Back when GM was throwing millions at stuff like that...private jets, topless restaurant dinners, gallons of booze...but, that's another tale for another day ...
Bob, welcome to the Forum. I can't imagine what it must have been like to work on the Fiero design! You will certainly be getting lots of questions from us, as well as advice. I am familiar only with the 2.8L so take this with a grain of salt. If the gas turned to sludge in the tank and lines shouldn't it also have done that in the fuel injectors et al?? Perhaps you may need to remove them and send out for cleaning and calibration. If you decide you want to do that I can post the contact info for the place I and several of us before me used.
John, I replaced the single injector nozzle. It's a throttle body. Spray pattern did not change.
Patrick, I have no fuel pressure gage, but the 2.5 only needs about 10-13 PSI per what I've read online. Pulling the fuel line into the throttle body the thing really pumps out a lot of gas in a short period of time. If nothing else the flow rate is great. Can't tell if the pressure is good enough to trip the pressure return valve. Should it trip normally? Gasoline is coming out clean and clear into the catch can.
I didn't actually design the suspension stampings. Those were done in Hartville, Ohio by Teledyne Monarch. My company designed and built the LVDT (transducer) gaging that dimensionally measured the stamped and welded suspension arm assemblies. Starting with a Chevy Chevette lower control arm and modifying it for the Fiero's front lower control arms things were whacky from the get go. As the design was twice reworked things got better, stiffer, stronger. But the money GM tossed at us was simply insane. Especially for a vehicle not really designed in-house. Test track sessions were fun. The un-built mules and prototypes were just wild. It's the T&E money that was just insane to a once young aerospace engineer assigned to work with an automotive project. I also remember the assembly line shut down for a few days (more than once!) because pieces parts did not even fit on the chassis going down the assembly lines. Hop a fast private jet from Akron-Fulton Airport to Pontiac and 20 minutes later all hands were on deck trying to get things working again! Fun times. Lots of red and white 1984 models (probably assembly line rejects) with huge numbers on the doors that anyone in need of transportation around the factory complex could jump in and drive to a meeting or whatever. Pretty cool stuff.
I really want to get the old girl back on the road for one last Summer fling. All four calipers are sticking from sitting so long, but that's child's play to loosen up or replace. The engine rough running, stalling thing has me stymied for now.
Did it sit with gas for that long? When I revived a 85 a while ago, the fuel hose that was in the tank from the pump to outlet turned to mush from sitting so long. May be something to consider.
ECM uses MAP, TPS, CTS, and IAT (? 85 Duke) inputs for starting/idling. O2 input once sensor is hot. MAP is affected by leaks in vacuum lines. Check all of those.
Coolant Temp Sensor (CTS) may have gone bad. Check its resistance across it's leads. IAT/MAT (air temp) too if you have one. If that's OK I'd inspect the O2 sensor as well.
Patrick, I have no fuel pressure gage, but the 2.5 only needs about 10-13 PSI per what I've read online. Pulling the fuel line into the throttle body the thing really pumps out a lot of gas in a short period of time. If nothing else the flow rate is great. Can't tell if the pressure is good enough to trip the pressure return valve. Should it trip normally? Gasoline is coming out clean and clear into the catch can.
Bob, I discovered that my '84 wouldn't run properly with 4 psi of fuel pressure. The symptoms I was experiencing were somewhat similar to yours. If you wish, you can read about it Here.
Did it sit with gas for that long? When I revived a 85 a while ago, the fuel hose that was in the tank from the pump to outlet turned to mush from sitting so long. May be something to consider.
It started out in 1999 with a full tank of gas. That must have gradually evaporated down to the 1" or so of stinky varnish crap that I mentioned above. All fuel lines were in good shape. I replaced the fuel pump pressure line (rubber) that ran from the sending unit to the line that takes the gas up to the throttle body because I had to cut that one to get it off the steel line. It was maybe 6" to 8" long and other than being stuck fast onto the steel it was in good shape. No lines were soft or mushy. New hose clamps were used everywhere even though that was just a precautionary move.
The old fuel pump looked good, felt good (not soft or deteriorated), but it was obviously not pumping so replacement was a no brainer. I have no means of checking the output pressure, but as I said above the flow rate 'looks' darn good with the fuel line disconnected at the throttle body and just running the pump and allowing the gas to to shoot into a catch can in the engine compartment. The 4-holer fuel pump only specs at 13 PSI so basically a very low pressure system.
Bob, I discovered that my '84 wouldn't run properly with 4 psi of fuel pressure. The symptoms I was experiencing were somewhat similar to yours. If you wish, you can read about it Here.
Very interesting.
I suspect this is also my problem as I also get no flow on the return line to the tank. I will drop the tank again and inspect the pump mounting, the hoses inside the tank, replace hoses and add hose clamps as required.
I've said all along to myself and anyone near me that would listen that the engine bogging, stuttering and not revving sounded like a fuel starvation issue. I did not think any of the sensors just deteriorated over the 20 years the car sat, but when I got the code 22 I replaced the TPS per the Fiero Store tech page instructions.
So, basically you guys are say I MUST have a return flow into the fuel tank in order to have enough PSI at the throttle body to properly feed the engine with enough gas? As I said earlier there has been no return line flow back into the tank. I will pressure test the output line if I can buy a gauge and adapter setup, but your analysis sounds like it might be my problem. And yes, the pump I installed is a Chinese Autozone $30 unit. The filter sock might also be coated with freshly loosened 'crud' that was still in the tank also.
I think a pressure test and tank drop are in my future. Thank you, sir!
ECM uses MAP, TPS, CTS, and IAT (? 85 Duke) inputs for starting/idling. O2 input once sensor is hot. MAP is affected by leaks in vacuum lines. Check all of those.
Coolant Temp Sensor (CTS) may have gone bad.
I had a CTS go bad on my '88 Cherokee and that caused a massive raw fuel dump and flooding to the point the engine would not even start. I will look at replacing the Fiero's CTS, but I don't think it deteriorated from sitting as I pulled it and the tip looked good. Never know until a voltage / resistance test though.
Will double check for vacuum leaks. None found to the MAP sensor so far or the EGR or anywhere else I went poking around.
No CEL and the only other code trip was when we disconnected the MAP sensor. Today I'm swapping in another MAP sensor and checking out the IAC, but I think a fuel pressure test and possible fuel tank drop is in my future if those don't fix the stumbling, stalling, lack of revving, etc.
An easy way to check fuel flow on an 84 2.5 is to take the air cleaner top off, get the car idling and rev it up by hand. If you don't see a huge increase in the gas flow pattern then you have a problem . My 85 had the rotten tube from the fuel pump up to the hard line, same as someone mentioned above. I have not seen any mention of the fuel pressure regulator but if you have no gas going out the return line you should check it.The problem might be too much fuel as opposed to too little fuel.
------------------ 86 GT built 2.2 ecotec turbo rear SLA suspension QA1 coilovers on tube arms
1988 GT 2.8, 5 speed. If rough idle, low power is an issue, wouldn't it throw a code, indicating which sensor is bad? Is there a code for a plugged injector?
I will pressure test the output line if I can buy a gauge and adapter setup...
I didn't bother with an adapter.
Some automotive supply stores have fuel pressure testers you can borrow.
quote
Originally posted by Patrick:
I disconnected the fuel filter (it was very clean inside) and connected a fuel pressure gauge onto the end of the fuel supply line. I then jumped terminal "G" at the ALDL connector with 12v from the cigarette lighter to run the fuel pump. The gauge showed a grand total of 4 lbs pressure while the pump was running, and immediately dropped to zero when the power was cut.
1988 GT 2.8, 5 speed. If rough idle, low power is an issue, wouldn't it throw a code, indicating which sensor is bad? Is there a code for a plugged injector?
I don't recall, but if it's possible to look at short and long term fuel trims for this OBD I system that should give a good indication as to whether it's leaning out, or flooding. I had a bad MAP sensor in a Fiero once that never set a code. It locked at a value just below part throttle and would idle and take off fine up to about half throttle and then fall over beyond the locked value as if a light switch had been turned off.
Someone here may recall the condition/circumstances, but I believe if the ALDL diagnostic terminals, A,B are grounded together, the engine light will flash at a frequency that corresponds to whether the fuel condition is rich, or lean with the motor running, as the rpms are raised a bit.
[This message has been edited by Joseph Upson (edited 01-10-2020).]
SO annoying to have to drop the tank again after you just replaced the fuel pump.
Yeah. I'm not 'oh so pro' when it comes to wrenching, but I take my time and at least try to cover all the bases when I have things torn down that far. The tank drop wasn't really all that bad...other than the stench of that rotten old gas! I watched a Youtube video or two on how to do it and got it safely lowered and ready to clean in in about an hour. It took longer to get the car up on jack stands and safety blocks in place.
Thanks to all of you guys for the advice so far! Seriously, the internet has made working on these somewhat complicated engine management systems easier and I think we should all be glad I'm not working on that Jeep 'Renix' (Renault-Bendix) POS system! That thing had me swearing in three languages and I ended up replacing every sensor on the thing before I figured out the temp sensor on the block was the incorrect unit for my vehicle! Talk about chasing my tail for a month...
I will get back under the Fiero tomorrow. Time to get it back up in the air today. No big deal. I'll flush the tank out a few more times, double check the fuel pump/sending unit work, inspect and replace any fuel lines that even look like they are problematic. Sure would be easier on a rack! LOL! My old back and shoulder blades feel like I lost a fight with a bear after sliding around on that cement floor!
Originally posted by CampyBob:My old back and shoulder blades feel like I lost a fight with a bear after sliding around on that cement floor!
I use sheets of cardboard from boxes from large purchased items when I'm on the cement or wood floor. So much easier to slide on & provides some cushioning.
[This message has been edited by David Hambleton (edited 01-11-2020).]
I'll flush the tank out a few more times, double check the fuel pump/sending unit work, inspect and replace any fuel lines that even look like they are problematic.
We don't know for sure that it's a fuel pressure issue. I hope you double-check the fuel pressure before dropping the gas tank for a second time.
I use sheets of cardboard from boxes from large purchased items when I'm on the cement or wood floor. So much easier to slide on & provides some cushioning.
I wore a heavy coat, but the kerosene heater got it so warm I was taking it off all the time. Cardboard is a great idea. Didn't have the car much more that 'the tank should clear things when I drop it using the trolley jack' off the floor. If I had raised it another 4"-6" I would have bought a creeper.
The thing that killed my shoulders was the fuel lines. It was a wrestling match to get the filler and vent and the three small lines off. The four AC line clip bolts and tank strap bolts were easy with the air ratchet. Lots of respect for real mechanics/service techs. They earn their pay, for sure.
A quick search here (hint hint ) turned up This thread.
Thanks, Patrick! Everything I read was saying 10 PSI minimum. I just wondered if all you much more experienced 2.5 / Fiero guys had something otherwise to say. Will try and find a low pressure test rig with a suitable test range.
Before dropping the tank I think I'm going to blow compressed air through every line I can get at to make sure nothing is soft, rotted or plugged. That lack of fuel down through the return line does have me concerned. That's a red flag, based on the replies above. Will also check spray pattern for increase in flow (visually with air cleaner off) as engine is revved up manually at the throttle body linkage.
Tony, to simply test what fuel pressure the system is able to provide, an adapter is not absolutely necessary. There is no need for the engine to be running. I posted the following earlier in this thread.
quote
Originally posted by Patrick:
I disconnected the fuel filter (it was very clean inside) and connected a fuel pressure gauge onto the end of the fuel supply line. I then jumped terminal "G" at the ALDL connector with 12v from the cigarette lighter to run the fuel pump. The gauge showed a grand total of 4 lbs pressure while the pump was running, and immediately dropped to zero when the power was cut.
[This message has been edited by Patrick (edited 01-13-2020).]
Yesterday a 0-100 PSI gauge would not even hit the 10 PSI mark. Guessing/interpolating it was 7 to 8 PSI. No clue as to the resolution of the low end of that scale, but repeatability was good.
I picked up what was 'supposed' to be a 0-15 PSI gauge from NAPA this morning. Despite the catalog describing the test set as 0-15 PSI it was actually a 0-10 PSI gauge. Bought it anyway and that pump I stuck in or the next replacement (if needed) better peg that gauge at 10 PSI+.
Just a WAG, but my money is still on either a partially pinched rubber hose, crud getting sucked against the fuel pump sock or the pump is by-passing inside the tank. Possibly at the rubber hose that connects the pump output port to the steel riser line on the sending unit. So far the pressure relief valve has still not been seen to trip fuel into the tank return line. That is a screaming red flag to me that says, "Not enough pressure".
Will have another go at it on Monday and report test result, but I can already see the tank coming down under that car again.
... or the pump is by-passing inside the tank. Possibly at the rubber hose that connects the pump output port to the steel riser line on the sending unit.
It was only a month ago that you had it all apart. What condition was the short length of hose at that time? Was it the proper submersible hose? Did you clamp it securely at both ends?
Patrick, The OEM short length (2"?) hose was NOT clamped at either end and I did not clamp it when I replaced the pump. So, no, I did not add clamps there. WILL add clamps on the re-installation of the replacement pump or an exchange pump if this one fails to correctly pressure test when out of the vehicle and tank.
The OEM hose was in good condition. Not soft. Good snug fit over both the fuel pump output port and the steel riser tubing. I re-used it.
Other than a ton of 'crud' in the tank from the remnants of the gasoline the inside of the tank and sending unit was in darned good condition.
Still, I'm guessing a bypass condition or more crud that I didn't get completely cleaned out of the tank fouling the strainer sock. Fuel at the inlet line to the inline filter is clean and clear. No crap coming out of the tank so if there still is some on the tank bottom it is not getting to the throttle body.
Air temp is 14 degrees this morning! Too cold to do anything major today, but I hope to hook up my new 0-10 PSI gauge and turn the key to Run and see what I get. Any bets that pump does not peg the 10 PSI mark on the dial?
Here's a pic of what was supposed to be a 15 PSI tester!
The Factory Service Manual suggests a flow test of 1/2 pint (236 ml) for 15 secs of pump action by grounding terminal G on the ALDL. Seems like a good test to run after the in-line filter.
It's reading 2-1/2 PSI on the tank side of the disconnected inline filter line. That, to repeat, is 2.5 PSI. Weird that it is flowing so well, but obviously my 'fuel starvation' diagnosis causing the stumbling, rough running and lack of RPM's was correct.
When the air temperature comes up the tank is coming DOWN!
And Patrick, I lied...or let's just say old age and memory failed me! I DID remove the two old black plastic ratchet style clamps that were on the 2" hose and installed the two new black plastic factory ratchet clamps that came with the fuel pump and held the 2" long piece of hose in place. My apologies, sir! The old clamps were in great shape, clamped positively and I now remember removing them. Found them in the new pump box with the receipt that I stashed in the trunk compartment.
So, I now doubt the pump is by-passing at the 2" hose area. Either the strainer sock is covered in filth, a line is partially pinched or plugged, the replacement pump is a piece of trash (doubt it ingested anything through the new strainer) or?
The Factory Service Manual suggests a flow test of 1/2 pint (236 ml) for 15 secs of pump action by grounding terminal G on the ALDL. Seems like a good test to run after the in-line filter.
David, Thank you!
As a guess, I would say the flow rate is pretty close to that and why the engine was 'almost' running OK. I could flutter that gas pedal and get it to 3,500 RPM, but no way would it stay running. It was running itself out of fuel...definitely a starvation issue.
The replacement pump is spec'd at a free flow rate of 49.9 GPH. or 1.65 pints per 15 seconds if I did the math correctly. With a minimum of 43.3 GPH flow rate that would be 1.44 pints per 15 seconds of run time.
With a specified pressure range of 12 to 26 PSI it should be pegging my new 10 PSI gauge...but, sadly, it is not even close at a 2.5 PSI reading.
The only area I can think that I screwed up was in replacing the fuel pump outlet line that is about 5" long and is located in between the steel line coming out of the sending unit to the steel line that runs under the firewall area and heads up to the inline fuel filter. For some reason I cut the new piece of hose about 2" longer than the OEM one. Maybe to give me more wiggle to get it over the steel firewall line when I re-installed the tank? Well, it turned out to be a bad idea as the increased length did not have enough free space above it and it almost seemed to pinch the hose a bit. I played around with during the initial install and I 'think' I had it to the point there was no kinking or pinching in that hose, but now I want to double-check that.
I think that would reduce the flow and before dropping the tank I'm going to try shortening the hose an inch or so. That's going to be a heck of a trick. Maybe pinch the hose off with Vice Grips if there's enough room and then cut the line to shorten it...all while holding a catch can while the line drains!
It wasn't the pinched 5" external line. I did have that routed fine.
But...
I re-used the short OEM 2" long line that couples the sending unit to the fuel pump. It felt fine. Not soft or mushy and it was a snug fit over the steel line and onto the pump output port. Seemed legit...
Unfortunately...when i put that initial 6 gallons of fresh gas in the tank it must have been enough to cover the 2" line that had been exposed to air for 20 years. THAT softened it up all right! It had a hole blown in the side of the hose!
If anything will drop your fuel pressure to 2.5 PSI that would do it! It also explains why the car ran and revved perfectly when it was still on jack stands 5 minutes after the fresh gas was added. My guess is that in the following 24 hours or so before I tried that second startup and all the problems appeared was enough time for the new gasoline to attack the rubber and that next starting of the vehicle was when the 26 PSI fuel pump pressure blew the hole in the line and the internal by-passing started. Explains the pressure being so low the fuel pressure regulator and return line was not tripped and functioning.
All this over a line I should have had the common sense to replace! LOL!
The inside of the tank looked good. No real tons of crud or anything I was kind of expecting to find. I guess I did a better job of flushing it than I thought. The strainer sock looked good.
I want to thank everyone for their help. Seriously, I appreciated every word of advice given! And the next time a guy comes into the forum asking what might be causing his rough running, failure to rev, stumbling condition after replacing the fuel pump you be sure and ask him to double-check the fuel pressure and make sure he changed out the 2" coupling line from the fuel pump! Tell him you know one idiot that did NOT!
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