1984 2.5 no power at times. (Page 1/2)
Tony Santucci MAR 31, 03:09 PM
Continuing on with the '84 Iron Duke driveability:

Sometimes the engine loses all power. If you open the throttle, it's not getting fuel. It's very intermittent. I was actually able to have it happen long enough today where I was able to pull the air cleaner lid and verify that when it's happening, there is hardly any fuel being injected. It came out of it before I could pinpoint the source of this failure.

It's been doing this very intermittently since I got it. New stuff: fuel pump, filter, ECT (both), MAP, TPS, IAC, injector, distributor and module, coil, cap, rotor, wires, plugs.
Timing is set properly at 8 degrees averaged between cylinders 1 and 4 with the timing connector jumped to ground.
I've replaced the timing cover and oil pan, the cam gear looks great.
Car has 89k on the clock.

I replaced everything myself except for the injector that was recently replaced by the previous owner trying to fix the no start which was actually no power to the ECM.
I replaced the other things over the course of a month or so, mostly just to retire the 40 year old parts, but this intermittent no power condition has persisted throughout.
It doesn't stall when it happens, it just doesn't go.

The check engine light doesn't come on, and there's no codes. Scan tool data looks normal, but again it doesn't happen regularly enough or last long enough to see the issue so far.

I'm kinda hoping it permanently fails. It would make it easier to fix.

Anyone have my silver bullet? To recap: When the condition occurs it appears the fuel injector does not deliver fuel properly resulting in a severe lack of power off idle.
Patrick MAR 31, 03:17 PM

I realize you've changed the fuel pump, but checking fuel pressure would seem to be in order.
Tony Santucci MAR 31, 03:28 PM
I have, but have not during the event. fuel pressure is on the high side of 13. It doesn't last long enough to check so far.. I'm probably going to fab up a way to have the gauge adapter more permanently installed as the fuel pressure test adapter I have for TBI cars is a log style that temporarily replaces the filter.

Also, I should note that all the fusible links are new as well.
Patrick MAR 31, 03:42 PM

quote
Originally posted by Tony Santucci:

I'm probably going to fab up a way to have the gauge adapter more permanently installed as the fuel pressure test adapter I have for TBI cars is a log style that temporarily replaces the filter.



Yeah, it's a challenge checking fuel pressure on a duke. It's so easy on the 2.8 engine.
Tony Santucci MAR 31, 03:59 PM

quote
Originally posted by Patrick:

Yeah, it's a challenge checking fuel pressure on a duke. It's so easy on the 2.8 engine.



As it turns out, my fuel pressure gauge has the fittings I need to put the gauge inline after the fuel filter. Just checked it. It's got 13 at idle, but if I snap the throttle it drops too much to be good. Pulls down to almost 5.

Thanks for showing me the forest through the trees!.

Now I have to figure out whether it's power related or a restriction.
cebix MAR 31, 04:10 PM
I'd also say fuel pressure first (did you replace the rubber hose in the tank that connects to the pump?) but wouldn't rule out the injector. No idea how to test those things though. I had a flooding issue at cold starts on my '85 2.5 even with low fuel pressure (leak in line) and it went away with a new injector.

Also years ago had a stalling issue due to that rubber fuel hose inside the tank being dry rotted. It sprayed lots of fuel inside the tank instead of pumping it to the TBI.
Patrick MAR 31, 04:10 PM

quote
Originally posted by Tony Santucci:

It's got 13 at idle, but if I snap the throttle it drops too much to be good. Pulls down to almost 5.



Very odd. I'll be curious to hear what you eventually discover!

When you turn off the engine, how quickly does the fuel pressure drop? It should hold for quite awhile.

[This message has been edited by Patrick (edited 03-31-2021).]

Tony Santucci MAR 31, 04:16 PM

quote
Originally posted by cebix:

I'd also say fuel pressure first (did you replace the rubber hose in the tank that connects to the pump?) but wouldn't rule out the injector. No idea how to test those things though. I had a flooding issue at cold starts on my '85 2.5 even with low fuel pressure (leak in line) and it went away with a new injector.

Also years ago had a stalling issue due to that rubber fuel hose inside the tank being dry rotted. It sprayed lots of fuel inside the tank instead of pumping it to the TBI.



Yes, that hose is new.
Tony Santucci MAR 31, 04:20 PM

quote
Originally posted by Patrick:

Very odd. I'll be curious to hear what you eventually discover!

When you turn off the engine, how quickly does the fuel pressure drop? It should hold for quite awhile.




It holds for a short time, but thinking back to my days of wrenching on TBI stuff that's pretty normal. The EFI systems that are 35 PSI+ will hold pressure for a while, but in my experience the low pressure TBI stuff really does not.

Patrick MAR 31, 04:36 PM

quote
Originally posted by Tony Santucci:

The EFI systems that are 35 PSI+ will hold pressure for a while, but in my experience the low pressure TBI stuff really does not.



Ah, interesting to know. I was basing my belief on how my GT and Formula hold fuel pressure (which is easy to check with the 2.8 engines), but I don't have the proper in-line fuel pressure tester fittings to use on my '84 duke.