I recently purchased an 86 GT (2.8L, Muncie 4 spd) that hasn't been on the road since 2010. I've gotten it running and driving. New brakes (calipers, rotors, hoses), fuel tank repaired, new sending unit/pump assembly from Rodney, oil change (10W30, MG filter), new temp sensor and connector from TFS, new Oil Sender switch, cleaned plugs, and timing checked in diagnostic mode (~ 10 deg BTDC). I did run a can of Berrymans through the fuel system before the full repair of the gas tank as well.
Now, the car starts and idles wonderfully. However, once its warmed up, it really wants to bog and stall from idle/stopped. The other issue I have is that it has very little power on acceleration.
I recently purchased an 86 GT (2.8L, Muncie 4 spd) that hasn't been on the road since 2010. I've gotten it running and driving. New brakes (calipers, rotors, hoses), fuel tank repaired, new sending unit/pump assembly from Rodney, oil change (10W30, MG filter), new temp sensor and connector from TFS, new Oil Sender switch, cleaned plugs, and timing checked in diagnostic mode (~ 10 deg BTDC). I did run a can of Berrymans through the fuel system before the full repair of the gas tank as well.
Now, the car starts and idles wonderfully. However, once its warmed up, it really wants to bog and stall from idle/stopped. The other issue I have is that it has very little power on acceleration.
What could be my issue(s)?
I would start with a new coil, cap, rotor, wires, and plugs to rule them out.
The airbox is another issue. The genius that owned it before me stuck a cone filter on the end of the stock tube that goes to the throttle body (finding a new stock filter housing isn't fun).
I've looked at the cap and rotor and they don't look worn at all.
Should be around 42 PSI with "key on". You should see 38-42 PSI at steady idle. If there's a big drop when opening throttle, you have a problem. . . ------------------ My World of Wheels Winners (Click on links below) 3.4L Supercharged 87 GT and Super Duty 4 Indy #163
[This message has been edited by fierosound (edited 04-17-2025).]
I recently purchased an 86 GT (2.8L, Muncie 4 spd) that hasn't been on the road since 2010. I've gotten it running and driving. New brakes (calipers, rotors, hoses), fuel tank repaired, new sending unit/pump assembly from Rodney, oil change (10W30, MG filter), new temp sensor and connector from TFS, new Oil Sender switch, cleaned plugs, and timing checked in diagnostic mode (~ 10 deg BTDC). I did run a can of Berrymans through the fuel system before the full repair of the gas tank as well.
Now, the car starts and idles wonderfully. However, once its warmed up, it really wants to bog and stall from idle/stopped. The other issue I have is that it has very little power on acceleration.
What could be my issue(s)?
you still got a cat? if so loosen the downpipe just infront of it, as for low power our 88 has had that for awhile and i reccomend checking your valve lash and egr pipe and then checking vacuum signal from there should be ~16 inches of vacuum if its stock with a dead steady needle
The airbox is another issue. The genius that owned it before me stuck a cone filter on the end of the stock tube that goes to the throttle body (finding a new stock filter housing isn't fun).
Is the IAT sensor connected? If so, where is it located (since it appears you no longer have the OEM air box in place)?
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Originally posted by balaseca:
Brand new pump and sending unit from Rodney.
"Brand new" means next to nothing. Check the fuel pressure.
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Originally posted by balaseca:
...timing checked in diagnostic mode (~ 10 deg BTDC).
Did you check to make sure that 0° on the timing scale actually lines up with the wide timing mark when #1 cylinder is at TDC? It's rather common for the outer ring of old harmonic dampers to slip... thus throwing off all the timing marks.
If all that checks out okay, I'd check the TPS next.
[This message has been edited by Patrick (edited 04-17-2025).]
The car currently does not have an IAT installed (on the list to be rectified). Plan is to temporarily zip tie it at the filter.
I will check the fuel pressure.
The timing mark and the scale line up well. I dont think there's been any slippage.
As to EGR, there are blockoff plates on both the intake and exhaust, no tube or valve there. The solenoid is plugged in, but one vacuum line is pluged with a small screw and the other still travels under the intake.
The car does have a Cat, and I've been thinking that may be of some issue.
The car currently does not have an IAT installed (on the list to be rectified).
Well, that's no good. The ECU relies on it for temperature readings of intake air.
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Originally posted by balaseca:
The timing mark and the scale line up well.
Line up well with what? Did you actually check to make sure the piston was at TDC. (Use something like a plastic straw inserted through the spark plug hole.)
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Originally posted by balaseca:
I dont think there's been any slippage.
I don't think you're trying hard enough.
[This message has been edited by Patrick (edited 04-17-2025).]
Yes, I verified with both a small screwdriver and a borescope. The wide slot in the balancer lines up with 0 deg at TDC on compression stroke for Cyl #1.
I know the IAT is an issue, but can it cause what I'm experiencing? Only happens after the car warms up. My other thought was residual gunk in my injectors. I know fuel system cleaner in a can is okay, but the car sat for 15 years, so I'm trying to pick the collective brain of the Fiero community. I normally stick to carbs. lol
Yes, I verified with both a small screwdriver and a borescope. The wide slot in the balancer lines up with 0 deg at TDC on compression stroke for Cyl #1.
Okay fine. Ya gotta know that we get all types of new members posting questions here. Some are mechanically knowledgeable, some... aren't.
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Originally posted by balaseca:
I know the IAT is an issue, but can it cause what I'm experiencing?
It can't be helping. When the engine is warmed up, it goes into closed loop operation... and that's when its relying on info from the sensors.
I doubt it's the cat. I've had a plugged cat, and it affected the engine mostly when the revs got up... which stands to reason as it couldn't breathe. Off idle was basically fine.
Have you checked that both banks of injectors are firing? There are two fuses, one for each bank. If only one bank is firing, the engine can almost seem fine while idling, but then falls on its face when trying to accelerate.
[This message has been edited by Patrick (edited 04-17-2025).]
It can't be helping. When the engine is warmed up, it goes into closed loop operation... and that's when its relying on info from the sensors.
I doubt it's the cat. I've had a plugged cat, and it affected the engine mostly when the revs got up... which stands to reason as it couldn't breathe. Off idle was basically fine.
Have you checked that both banks of injectors are firing? There are two fuses, one for each bank. If only one bank is firing, the engine can almost seem fine while idling, but then falls on its face when trying to accelerate.
I know that the fuses are good, but actually haven't checked to see if both banks are firing. What's the best way to check that?
The car seems to have no issues on open loop (aka right when cranked, and at WOT). It's that right off idle that really kills it. Also, there's light surging when holding a steady speed (around 25-30mph).
I know that the fuses are good, but actually haven't checked to see if both banks are firing. What's the best way to check that?
A noid light, I guess... but I've never used one myself. What I have done is used a mechanics stethoscope with the metal probe attached and listened to each injector individually to make sure it was clicking. And that was after checking the resistance of each injector to make sure they were all in spec.
I just wanted to mention that the reason for doing a fuel pressure test is two-fold. Yes, it shows the fuel pressure while the engine is running... but just as importantly, it shows how quickly the fuel pressure drops when the engine is turned off. It shouldn't drop quickly. It should maintain pressure for... oh, I dunno... ten minutes or so before slowly dropping. Quickly losing fuel pressure could possibly indicate stuck open and/or leaky injectors.
[This message has been edited by Patrick (edited 04-17-2025).]
As to EGR, there are blockoff plates on both the intake and exhaust, no tube or valve there. The solenoid is plugged in, but one vacuum line is pluged with a small screw and the other still travels under the intake.
There are differing opinions, however I suggest verifying if the ECM chip was reprogrammed to override the EGR solenoid input.
Well, I did the pressure test. 41 PSI with key on and engine off. After 10 mins, it had dropped 6 PSI.
New cap and rotor, still bogs badly if you stomp on the pedal (or even just get on the gas). Pretty much have to rev up the motor slowly from a stop or it will just sit and stumble all over itself till you let off the gas totally.
Well, I did the pressure test. 41 PSI with key on and engine off. After 10 mins, it had dropped 6 PSI.
IMO, that's dropping way too fast. I'm not saying that this is necessarily the reason for the symptoms you've mentioned, but I suspect you've got at least one leaky injector... or that short length of hose in the fuel tank is possibly leaking.
Have you checked the TPS? What you're looking for is dead spots, and I believe at idle it's supposed be .5v
And then there's the MAP sensor. It'll definitely cause a bog if it's faulty, but I don't know the procedure to check it.
IMO, that's dropping way too fast. I'm not saying that this is necessarily the reason for the symptoms you've mentioned, but I suspect you've got at least one leaky injector... or that short length of hose in the fuel tank is possibly leaking.
Have you checked the TPS? What you're looking for is dead spots, and I believe at idle it's supposed be .5v
And then there's the MAP sensor. It'll definitely cause a bog if it's faulty, but I don't know the procedure to check it.
Firstly, Patrick, Thanks for all the timely help!
I put some Marvel Mystery Oil in the tank to see if lubing up the fuel system might help things. Any other advice on a leaky injector?
The TPS goes from about .5V to 4.7V smoothly through the whole range.
Havent checked the MAP, but have heard that they're cleanable? I think...
Another thing I've noticed is that my exhaust is WAY quieter than all the stock exhaust videos on the ole YouTube. Flow seems good when revving, but I'd expect a little more (a lot more, really) oomph from the motor than I'm getting
The airbox is another issue. The genius that owned it before me stuck a cone filter on the end of the stock tube that goes to the throttle body (finding a new stock filter housing isn't fun).
I've looked at the cap and rotor and they don't look worn at all.
This might be an issue too... there is an Intake Air Temperature sensor that's supposed to be installed in the air cleaner assembly. If this is not connected or... who knows where it is? Then it's not properly reading the temperature of the incoming air.
Newer cars which have a MAF (Mass Air Flow sensor) have one of these built in, right in the center of the MAF sensor... and it's a critical component for the ECM to properly regulate fuel per the temperature of the incoming air. If it's just dangling, or worse... hanging just above the exhaust Y-Pipe, it's going to be giving REALLY bad readings which will dramatically affect the fuel mapping.
EDIT: Sorry, didn't read the other responses before I responded. 100% what Patrick said, the IAT is a concern. Having it disconnected is a problem. It directly affects the amount of fuel that the engine gets, and it must rely on other things instead. As Patrick said... when the engine is not warmed up, it's running "off the tape" so to speak. Once it's warmed up, then it relies on the sensors. If you've ALSO removed the EGR valve... that too affects the fuel map, since the engine expects a certain amount of exhaust gasses being cycled back into the engine... which also lowers combustion temperatures, and affects how much or how little fuel is needed. To actually remove the EGR valve, it would need the ECM to be reprogrammed otherwise you'll be running lean at different points.
[This message has been edited by 82-T/A [At Work] (edited 04-18-2025).]
I have plugged in a new IAT, undecided on the best place for it though (besides the airbox that I'm looking for haha).
I'd love to get an EGR setup for the car, but though I can find a valve and a tube, the part that goes from the exhaust piping to the EGR valve and allows the tube to be in place is something I just dont have any clue where to find.
I have plugged in a new IAT, undecided on the best place for it though (besides the airbox that I'm looking for haha).
I'd love to get an EGR setup for the car, but though I can find a valve and a tube, the part that goes from the exhaust piping to the EGR valve and allows the tube to be in place is something I just dont have any clue where to find.
Ugh, yeah... I just looked on eBay for you... and couldn't find any of that stuff. Normally that stuff is all available... I'm surprised none of it is on eBay right now.
Ya gotta know that we get all types of new members posting questions here. Some are mechanically knowledgeable, some... aren't. 
