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.
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.
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.
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.
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.
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.
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.
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.
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.
I've owned this gauge set for 20 years. Never realized it came with the fittings to do this. You learn something new every day!
[This message has been edited by Tony Santucci (edited 03-31-2021).]
Does it have a cat or a test pipe? Cats can cause very intermittent problems ie plugged / not plugged. '84s are also notorious for having the fusible links rot out where they connect to the starter motor although you may have already addressed that...
Does it have a cat or a test pipe? Cats can cause very intermittent problems ie plugged / not plugged. '84s are also notorious for having the fusible links rot out where they connect to the starter motor although you may have already addressed that...
There is no cat. All the fusible links are new. That was the original no start problem. It's definitely not holding fuel pressure properly under load. Maybe something was kicking around in the tank that I didn't notice when I had the fuel sender out of it. I'm going to check that the fuel pump circuit maintains proper voltage first before I drop the tank again. The joy of 40 year old cars!
Check or replace the fuel pressure regulator. It sounds as though it is working erratically
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Check or replace the fuel pressure regulator. It sounds as though it is working erratically
I was thinking that too. Anyway, here's what happened... I started with making sure the fuel pump was getting proper current, found that the ground wire resistance was a bit high at 18 ohms. Cleaned the engine ground and squared that away. Then I put the gauge inline before the fuel filter. Same issue, fuel pressure a touch low, doesn't hold well under load. I pinched off the return line, no difference. The fuel pressure gauge set has a shutoff on it, so I jumped the fuel pump to power and dead headed the fuel pressure line. Sometimes the fuel pump would push 20 PSI, other times it would just make a terrible noise and not reach 10 PSI.
Just replaced the fuel pump. again. I ordered a Delphi this time. Now it's got 15 key on engine off, and the fuel pressure holds steady under load. I'm calling this one fixed.
On a positive note: I can have the fuel tank out and back in on this thing in like 12 minutes now, so there's that. Good practice, I guess....
Just replaced the fuel pump. again. I ordered a Delphi this time. Now it's got 15 key on engine off, and the fuel pressure holds steady under load. I'm calling this one fixed.
Just so people know what to avoid... what was the brand of the new fuel pump that was causing issues?
AFAIK, Precision is a seller of US made fuel pumps. Did you install the pump with a pulsator or with a short section of J30R10 submersible fuel injection line? My guess is still on the regulator, wiring or the injector itself.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
AFAIK, Precision is a seller of US made fuel pumps. Did you install the pump with a pulsator or with a short section of J30R10 submersible fuel injection line? My guess is still on the regulator, wiring or the injector itself.
It was installed with a straight hose. 1984 didn't use a pulsator.. The new fuel pump has been in for some days now and the issue is no longer present. The engine runs very well now. As far as Precision Fuel Pumps goes, I don't know. It's the first one I ever bought, and likely the last. The Delphi i replaced it with by all appearances is a much better piece. Just looking at it you can tell the difference in build quality. Also, the in tank plug for the pump needed to be replaced as well. The pig tail that came with the Precision had much smaller gauge wire. Fuel pressure is rock solid 12 PSI all the time while running now, no more dip to 5 PSI under load.
Precision Fuel Pumps: 0 out of 5 stars. Would not recommend.
