john d Posted March 10, 2022 Share Posted March 10, 2022 Hello to everyone. I've a new problem, need assistance before heading to Charlotte for rally. Vehicle runs perfect for roughly any duration that oil pressure is reading high. When it reads low cuts out fuel pump, as it should. Changed sensor. New one never goes above half on gauge. Original did go to full on gauge, for five years of ownership, never moving downward until now. New switch still shutting down fuel pump. Will change connector tomorrow. Have changed oil filter, in case it was defective, gauge still only going to half. Intend to change oil tomorrow as well. Crank case is filled to correct capacity. I have 400 test miles on vehicle since problem, so I'm pretty sure I'm still pumping oil. Vehicle starts right up after stall, may have to stay in gas thou, not always. Original switch and connector very oily and contaminated but not a drip leak. Link to comment Share on other sites More sharing options...
Ronnie Posted March 10, 2022 Share Posted March 10, 2022 I would swap out the fuel pump relay and see if that cures the problem with the engine dying. Link to comment Share on other sites More sharing options...
john d Posted March 10, 2022 Topic Author Share Posted March 10, 2022 thank you did that also Link to comment Share on other sites More sharing options...
Ronnie Posted March 11, 2022 Share Posted March 11, 2022 1 hour ago, john d said: Vehicle runs perfect for roughly any duration that oil pressure is reading high. When it reads low cuts out fuel pump, as it should. Changed sensor. New one never goes above half on gauge. Original did go to full on gauge, for five years of ownership, never moving downward until now. New switch still shutting down fuel pump. Something must be causing the problem besides the oil pressure sender or it's wiring. The engine will start and run with the sender unplugged. Read this thread and you will see what I mean. Link to comment Share on other sites More sharing options...
2seater Posted March 11, 2022 Share Posted March 11, 2022 How are you determining the fuel pump quits when gauge indication is low? Not doubting what you said, just curious as to how? Fuel pressure gauge on rail, install indicator on the green fuel pump bypass wire or some other way? Conversely, you could hot wire to the fuel pump green connector and take the operating system for the pump out of the equation also. The oil pressure sender reading high on a '90 is a relatively common problem but usually has no effect on engine running. There are two sets of connections in the sender, one for the gauge and one for the fuel pump. If it is indicating correctly, oil pressure must be quite low to affect fueling. Link to comment Share on other sites More sharing options...
john d Posted March 11, 2022 Topic Author Share Posted March 11, 2022 Have not put fuel pressure gauge on system. When problem first occurred I chose to change pump, filter screen and relay, assuming all are 32 years old. I thought that system has safety , oil pressure drops pump quits. Noticed switch and connector wet and changed. Can put gauge on fuel rail but would seem that original and new pump would have correct pressure when stall occurs since problem exists with both. This does seem to be electrical. Vehicle will fire right back up and oil pressure returns to half with new switch, may need to keep rpm at 1000 to continue to run. Seems all of this only happens when car is hot. Link to comment Share on other sites More sharing options...
2seater Posted March 11, 2022 Share Posted March 11, 2022 I guess there are two things to verify, actual oil pressure with a gauge and if the fuel pump is losing power at some point. Oil pressure to cause fuel pump cutout is <6psi per the FSM. Link to comment Share on other sites More sharing options...
john d Posted March 11, 2022 Topic Author Share Posted March 11, 2022 Don't have oil pressure gauge. Pulled relay to check oil pressure. Vehicle cranks longer at start up (without relay) Once pressure is reached she fires. Just took a test ride problem of course getting worse. Link to comment Share on other sites More sharing options...
DAVES89 Posted March 11, 2022 Share Posted March 11, 2022 i agree with Ronnie. you guys are in the forest looking for the trees nd it's something else. Do you have the original ignition module? I would start there. 1 Link to comment Share on other sites More sharing options...
Ronnie Posted March 11, 2022 Share Posted March 11, 2022 6 hours ago, john d said: Just took a test ride problem of course getting worse. You would be better off if it would quit running and not start. Much easier to troubleshoot than if it randomly stalls and starts right back up. Link to comment Share on other sites More sharing options...
Padgett Posted March 11, 2022 Share Posted March 11, 2022 " it reads low cuts out fuel pump" Common mythconception. A 3800 gauge sender has two elements (and a four pin connector). The gauge sender which is variable, and a switch set for something between 6 and 10 psi. It is the switch that turns off the fuel pump. The are also a number of sensors for 3800s. The LG3 is set for a 40 psi relief. The L27 is set for 60psi. Both are calibrated for a 1ma gauge. Can watch when cool and see the relief setting as a hiccup in the gauge as you bring the revs up. Link to comment Share on other sites More sharing options...
john d Posted March 11, 2022 Topic Author Share Posted March 11, 2022 appreciate all input, intend to look to ignition module next. Have changed one about 5 years ago. Link to comment Share on other sites More sharing options...
Ronnie Posted March 12, 2022 Share Posted March 12, 2022 Throwing parts at it until you find the right one can get expensive. The first thing you need to know is if it is losing fuel pressure, spark, or both when the engine dies. I would connect a 12 volt light bulb with a length of wire to the green prime/test connector and put the bulb somewhere you can see it while driving. That light should be burning anytime the fuel pump is getting power either from the fuel pump relay or the oil pressure sender/switch. That will tell you if the fuel pump is losing power when the engine dies. I would also carry a fuel pressure tester and check the fuel pressure right there on the side of the road when it dies before cranking the engine back up again if possible. Here is something to consider. If the ICM is bad you will only lose spark. If the crankshaft position sensor fails you will lose spark and the fuel injection system will shut down to, including the pump. You could have a crank position sensor going bad. 1 Link to comment Share on other sites More sharing options...
DAVES89 Posted March 12, 2022 Share Posted March 12, 2022 I have a fuel pressure tester and when I was having issues I snaked the hose over the engine and under the hood and taped the gauge to the windshield. That way I had a constant reading of what was going on. 2 Link to comment Share on other sites More sharing options...
john d Posted March 12, 2022 Topic Author Share Posted March 12, 2022 Like the light bulb suggestion, where is location on test wire again? Have fuel pressure gauge and may try either b4 going after ICM Link to comment Share on other sites More sharing options...
Ronnie Posted March 12, 2022 Share Posted March 12, 2022 44 minutes ago, john d said: Like the light bulb suggestion, where is location on test wire again? Fuel Pump Prime (Test) Connector Location Link to comment Share on other sites More sharing options...
john d Posted March 12, 2022 Topic Author Share Posted March 12, 2022 new plan. Water pump is five years old, I drive it very regularly, probably 60k on it. Going to change it, cam sensor as well and inspect magnet. I know I can change sensor without changing pump. I have no codes, 041 cam sensor. Also she has 187,000 on her. Found fuel pump test wire. Thanks again to all!!!!!! 1 Link to comment Share on other sites More sharing options...
Ronnie Posted March 12, 2022 Share Posted March 12, 2022 That was an unexpected plan. You have an engine that is stalling and on the point of leaving you stranded on the side of the road and you decide to change the water pump. I really didn't see that coming. 😁 2 Link to comment Share on other sites More sharing options...
john d Posted March 12, 2022 Topic Author Share Posted March 12, 2022 Ronnie the water pump change out is only a preventive move. If I'm removing the pump pulley to make the inspection and change out of cam sensor and magnet easier, I want to change the pump. My next plan is to check air pressure to see if that helps with stalling. 😁 Link to comment Share on other sites More sharing options...
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