When I first got my '88 the oil pressure gauge was pegged right whenever the key was on. I replaced the sender with one from Rock Auto and it worked perfectly, for 2 weeks, then it pegged right again.
I then ordered a Delco sender, replaced it, and it lasted 3 days. Ok, I'm thinking I'm just having bad luck? I get one more Delco sender and it just dies after 2 weeks.
Any ideas for what I should check? I don't want to keep throwing sending units at it.
Do what he said. might work or not. The plug could be bad or wires to it and also wreck the sender.
Metripack (and Weather pack) plugs can has problems because isn't "water proof" only "Weather resistance." Seals won't protect pins etc when soak in polluted water etc. even if dries out later, "rust" and chemicals can still eat metal parts.
If plug is crap then just install new pigtail using weather proof crimps w/ glue inside heat shrink at minimum.
See my Cave, Oil Sensor Sender ground is metal going into engine.
------------------ 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)
Usually, a bad ground can cause the gauge to peg. To test this, when you have a known good sender, unplug the harness with the ignition on and watch the gauge.
Originally posted by fierofool: Usually, a bad ground can cause the gauge to peg. To test this, when you have a known good sender, unplug the harness with the ignition on and watch the gauge.
Iffy plug or wires can do same. Iffy gauge and resistor can make problems too. Resistor is on the back of gauge hidden inside of dash. gauge clips holding the bolts and dash "board" on back of dash can cause problems too. The clips may look good but make crap connection between gauge and board.
Can short the gauge to ground for 0 on gauge I think. But make sure of is sender pin. Others is Fuel pump and short 1 pin of them to ground blows FP fuse at minimum.
cave page has pin out for 88 plug is why to read even w/o "upgrade" for older cars.
Multiple Senders doesn't fail this way. Plug/wire w/ problem can wreck them. Example: If shorts FP switch wires to sender wire can wreck sender and maybe gauge.
Bad sender sender ground is hard to do but possible.
Check sender Ω. 0Ω = 0 pressure, 90Ω = max pressure. 45Ω is half scale. Should be 0Ω between pin A and engine w/ engine off. If true use a needle poke thru Tan wire plastic should be same connected to sender. If true wiggle tan wire watching Ω meter. should stay at 0Ω.
Check other senders pin A to metal bottom for 0Ω. It all are open, wiring/plug problems are very likely. Sender part can't handle power on FP switch and fries fast when has plug/wire problems.
Gauge "reads" sender's 0 to 90Ω. Gauge pegs if sender or wire is disconnected. Gauge can read off, way off, or even peg if sender wire is iffy or body to engine grounds are iffy. Temp gauge should read off to way off too when has engine ground problem too. Volt meter in GT cars can have same plus iffy HL lights etc.
Sender wires go thru C500 and more on the way to the gauge. Any plug along the way can have a crap connection cause a peg gauge.
[This message has been edited by theogre (edited 02-07-2020).]
I unplugged it and put a meter on the sender. The center pin reads infinite resistance as soon as I start the car and 0 ohms when off. I'm guessing that means the sender is bad?
Oil pressure does not go through C500, it goes through the C203. Check the fingers on the flexible circuit board (dash pod) for delamination and shorting to other circuits.
Today I got home from a short trip (in a different car) and when I walked by the Fiero I heard the buzzing of the fuel pump. The sender failed in such a way that the fuel pump was running continuously even without the key.
I'm guessing that's not caused by the gauge.
[This message has been edited by tmadia (edited 02-09-2020).]
I'm reviving this thread hoping that a solution to this was ever found. I upgraded my 86 GT oil pressure sensor to the 88 sensor (per Ogre's instructions on his 88 oil sensor upgrade web page) and 3 of them have burned out on me in a matter of 3 months. Each one worked fine for 2-3 weeks and the oil gauge needle started fluttering before the unit finally quit.
Today I got home from a short trip (in a different car) and when I walked by the Fiero I heard the buzzing of the fuel pump. The sender failed in such a way that the fuel pump was running continuously even without the key.
I'm guessing that's not caused by the gauge.
That's a known problem reported in the past with the 1988 style oil psi sender, because basically they are a really crappy part. (yes even the AC Delco ones)
quote
Originally posted by SunsetChaser:
I'm reviving this thread hoping that a solution to this was ever found. I upgraded my 86 GT oil pressure sensor to the 88 sensor (per Ogre's instructions on his 88 oil sensor upgrade web page) and 3 of them have burned out on me in a matter of 3 months. Each one worked fine for 2-3 weeks and the oil gauge needle started fluttering before the unit finally quit.
Any follow up on this issue?
That is also a known problem and why I don't recommend changing a 1985-87 oil psi switch to a 1988 style switch, you are better off just keeping the original 1985-87 style oil psi switch despite the "claims" of the 1988 oil psi switch being better, because the 1988 one is even MORE problematic in my opinion.
PS: Side note... Same can be said about the older 1985-87 SI alternator "upgrade" to newer style 1988 CS alternator, which isn't an upgrade at all when you honestly evaluate the totality of it all. Sure, it puts out a little more power if you are running a lot of aftermarket accessories and/or doing a ton of stop-n-go traffic or using at night, but older alternator is a much higher quality unit and better built product all around, and can handle the heat better. These "upgrades" are not a one-size-fits-all.
There is also a popular misconception in the "non-Fiero automotive community" that the 1988 Fiero is wonderful and the 1987 and older Fiero's are crap, lol. Sure, the 1988 suspension is much improved on, but there are disadvantages to the 88's (i.e. oil psi switch, alt, wheel bearings, master cylinder, elimination of coil/alt cooler, spindles, wheel choices, parts availability, costs, and so on). There are many advantages of owning a pre-1988 Fiero depending how you plan on using the car.
[This message has been edited by Skybax (edited 03-10-2022).]
Where you got the senders? Ebay Amazon and others have counterfeit problems.
E2A---> Are you sure it really the sender? When you pull a plug often it disturbs other things. Dash gauge and wiring often have problems too and replacing old or new senders often won't help.
Put Ω meter on Pin A and base or anywhere on the engine block then run the engine. Sender output 0 - 90Ω But Good pressure should see ~ 40-45Ω
[This message has been edited by theogre (edited 03-10-2022).]
Originally posted by Skybax: That is also a known problem and why I don't recommend changing a 1985-87 oil psi switch to a 1988 style switch, you are better off just keeping the original 1985-87 style oil psi switch despite the "claims" of the 1988 oil psi switch being better, because the 1988 one is even MORE problematic in my opinion.
PS: Side note... Same can be said about the older 1985-87 SI alternator "upgrade" to newer style 1988 CS alternator, which isn't an upgrade at all when you honestly evaluate the totality of it all. Sure, it puts out a little more power if you are running a lot of aftermarket accessories and/or doing a ton of stop-n-go traffic or using at night, but older alternator is a much higher quality unit and better built product all around, and can handle the heat better. These "upgrades" are not a one-size-fits-all.
There is also a popular misconception in the "non-Fiero automotive community" that the 1988 Fiero is wonderful and the 1987 and older Fiero's are crap, lol. Sure, the 1988 suspension is much improved on, but there are disadvantages to the 88's (i.e. oil psi switch, alt, wheel bearings, master cylinder, elimination of coil/alt cooler, spindles, wheel choices, parts availability, costs, and so on). There are many advantages of owning a pre-1988 Fiero depending how you plan on using the car.
When you upgrade sender to 88... If the sender dies, 88 won't dump oil on the road and Empty the pan quickly as old ones can and has done to many people. I have old ones fail doing just doing that enough time to know first hand. Just for my own car had to replace every 2-4 years w/ old one. Haven't replace 88 sender in 10+ years since upgrading... If you find an old "gen1" unit to replace... often is very old stock or made in china or other 3rd world and diaphragm won't last. And that's senders even from known parts stores!
12SI is Good? No. SI Many Problems and Eats More Engine Power to Generate Less Amps at all points in the load curve. I've replace many SI w/ F'd Diode Trio and more. Very few know why SI have the Infamous Diode Trio that dies and kills the battery fast. IOW When the Diode Trio fails, you hope to figure out fast, disconnect the battery and then call for a tow. If you don't you will replace the alt And often Battery too. Unlike Most others including CS, when they die often can drive a lot with a dead alt and their not killing the battery at same time.
And doesn't mean battery is low... Bad Diode Trio and Gen1 HL motors w/ problems can drain the Battery to 0v and destroy it. As is, Starting Batteries do not like being drained below 10-11v w/o major shorting the lifetime.
And 88 Fiero isn't only one w/ CS alts. 87 Fiero 4cyl and other models had them first as part of killing off SI family. New GM often still use CS complete or "CS" format cases and other parts but change the regulator and name and tied into PCM as well.
But will agree 88 has many problems... frame changes was good idea but bad execution and worse cancelled the car so many parts dried up 20+ years ago. Just one big example was the front "hubs" that only 88 Fiero uses. Likely found another knuckle from another vehicle to fit "advance" suspension and made a custom hub to fit FWD/4WD knuckle.
tmadia, I have had the same repeated problems you have experienced. I've been through about 5 senders. They either blow the instrument panel fuse, or make the fuel pump continue to run. Even if they aren't bad right from the box, they fail in short order. I just got tired of the hassle and unplugged it and let the gauge peg full right. I even changed out my gauge set to no avail.
I've checked the wiring. Initially I used the butt connectors that came with the pigtail but then I simply soldered the wires together and sealed them with heat shrink tubing.
The first sensor was from ebay, the second from walmart and the last one from Rock Auto. All 3 had the same failure rate.
Also I'm not sure if this is relevant but I should note that when the key is in accessory mode, the needle shows just above the red on the oil gauge (towards the left). It's only when I crank and start the engine that the needle is pegged far right until I shut the engine down. Maybe a clue as to how they might be failing?
quote
Originally posted by theogre:
Check the wiring again.
Where you got the senders? Ebay Amazon and others have counterfeit problems.
E2A---> Are you sure it really the sender? When you pull a plug often it disturbs other things. Dash gauge and wiring often have problems too and replacing old or new senders often won't help.
Put Ω meter on Pin A and base or anywhere on the engine block then run the engine. Sender output 0 - 90Ω But Good pressure should see ~ 40-45Ω
Crappy oil pressure sending units have been a problem in these cars for decades, they're probably all made by the same supplier that has been doing it wrong for a LONG time.
Respectfully disagree, while the CS puts out more amps its not worth sacrificing all the Si good stuff, especially when a Fiero is stock with 99% daylight driving...
CS alternators produce a LOT more heat They have a greater tendency to fry their bearings Weak electrical components Multiple plastic parts prone to failure Integrated parts = disposable junk Doesn't wear well
Si better cooling (more important on mid-engine) Heavy duty construction Better heat shield (more important on mid-engine) Completely rebuildable with "quality parts" Rectifier bridge can handle more heat More mileage
If you put a CS and Si side-by-side, open them up, anyone can see the night & day difference. So if somebody wants to convert from Si to CS for more amps go for it, but nobody can claim its "better" because that is simply not true. The same can be said for switching from points & condenser to Petronix on a 60's car, sure its convenient and you never have to adjust it (lazy), but its a cheap POS and when it-fails it-fails, whereas a quality set of points & condenser are extremely reliable mechanical parts, will get you home even if they rarely malfunction, and can rev cleanly to 5500 rpm (my dual point dist on modified 289 can rev clean to 6500 rpm) and only need to adjust/set the dwell once a year. My original point was, an "upgrade" doesn't always result in "better" as claimed, its relative to risk evaluation, so I would rather use the originally designed 85-87 oil psi sender that works like a refrigerator for decades before leaking, than a 1988 pos oil psi sender that electrically malfunctions in a variety of ways.
[This message has been edited by Skybax (edited 03-14-2022).]
Today I got home from a short trip (in a different car) and when I walked by the Fiero I heard the buzzing of the fuel pump. The sender failed in such a way that the fuel pump was running continuously even without the key. ...
I had a brand new sender to do exactly the same thing. (My previous sender killed the battery when it stuck, and kept the pump running.) I finally got tired of the silliness, and moved the fuel pump fuse circuit to the "ign" side of the fuse box, instead of the "batt" side. (Involved a bit of cutting/splicing/soldering behind the fuse box.) If you have a high current / high volume pump, this might not be advisable, but on my installation, it has never caused me a moment's trouble.
I finally got tired of the silliness, and moved the fuel pump fuse circuit to the "ign" side of the fuse box, instead of the "batt" side. (Involved a bit of cutting/splicing/soldering behind the fuse box.)
Not trying to totally derail this thread , but I'm wondering if that might also be a good idea for the '84-'86 headlight motor circuit? Might prevent a dead battery... or worse.
Crappy oil pressure sending units have been a problem in these cars for decades, they're probably all made by the same supplier that has been doing it wrong for a LONG time.
There's at least 2 different sources for the 88 style sender, because I've had a few BWD senders that gave low pressure alarms at a hot idle (incorrect per comparison with mechanical gauge), and 3 Delcos that all gave valid readings. There's a distinct difference in how the 2 brands are calibrated. I agree they're all unreliable though. The one nice thing about the 88 style is that it's easier to change (it's skinny enough you can put a socket over it). Other than that I'm not sure it was a good idea to convert, but I already did it. I'll never know if the older style would have been as failure prone as the 88s have been.
Apparently I haven't had near as much trouble as some people here though. Mine have lasted a few months to years each, not days to weeks like I'm reading here.
If there's any external factor causing these things to fail faster for some people, then this is all I can come up with:
are you using dialectric grease on the electrical connector to keep water out? is your charging system working properly? Check voltage with a multimeter, look for high voltage excursions. Check your peak (cold) oil pressure with a mechanical gauge. I don't remember if the bypass is set for 60psi or 80psi, but it definitely shouldn't go into the 100s and the sender might not be happy if it does. If you check that, go ahead and check the minimum hot idle pressure too. Then you'll know more about the health of your engine and how accurate the dash reading is at the low end of the scale.
As above, I strongly prefer the AC Delco senders because they are more accurate at the low end of the scale. The BWD senders I've used were in single digits (turning on the Oil warning light) when the mechanical gauge was still showing 20s.
To test the dash gauge, try plugging a resistor into the connector and see if the gauge responds correctly. I don't remember the exact scale but it's close to something like 1ohm per psi. A 68-75ohm resistor should give a near full scale reading. The exact scale might have been posted somewhere. You'll need to use multiple resistors in parallel because of the current draw - use the parallel resistor formula to get the resistance you need. Otherwise be ready for the resistor to start burning as soon as you plug it in.
Originally posted by SunsetChaser: I've checked the wiring. Initially I used the butt connectors that came with the pigtail but then I simply soldered the wires together and sealed them with heat shrink tubing.
The first sensor was from ebay, the second from walmart and the last one from Rock Auto. All 3 had the same failure rate.
Also I'm not sure if this is relevant but I should note that when the key is in accessory mode, the needle shows just above the red on the oil gauge (towards the left). It's only when I crank and start the engine that the needle is pegged far right until I shut the engine down. Maybe a clue as to how they might be failing?
Gauge pegged and stays is usually open something on the sender and wire between them.
Saying Rock Auto is meaningless because have different makers and PN even by same brand like Standard has xxx and xxxT w/ T numbers is cheaper and days of warranty.
IF all senders OP section is open on a meter... (Ω meter say OL etc not 0-90Ω for A to Base.) could be crap senders or gauge have problems and frying the senders.
Senders run on "12v" but not Direct "12v." A iffy gauge or a "soft" short to 12v otherwise can let too many amps flow and fry the sender.
Note that the Gauge have a resistor on back of it and not covered in any service doc including FSM. That resistor could have problems and so can the dash in several places... Common Examples: Gauge resistors and "nuts" get loose, dirty, etc. Do Not over tighten or can wreck the resistor or gauge. Big plugs on back and "board" go into like to bend the copper when "glue" fails on the board. SS spring clips can have problems on the board side, bolt side holds the gauge bolts, or both.
The dash gauges often lie even when have good sender because of same problems. My gauge often reads ~ 80psi even w/ 42-47Ω resistor to emulate ~ half scale sender. Check the dash and even Replace the gauge didn't help. Something else in gauge wiring is loose etc but not digging thru the entire car to find whatever is wrong.
, but I'm wondering if that might also be a good idea for the '84-'86 headlight motor circuit? 
