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Old 03-25-2022, 07:14 PM   #1
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93 Pace Arrow 454, fuel to the TBI but no spray

It sits on a P30 chassis and Ihave been able to resolve the transmission issues and she drives so much better. Until 5 days ago. I gave the fuel attendant $200 and told him regular unleaded please then went inside for some cold drinks and smokes. Upon return I jumped in the drivers seat and proceeded to drive away from the gas station. I made it 3 blocks before it died. I was half full of diesel. I was down to maybe 5 gallons of gas when I stopped at the gas station. Long story short, everything has been taken out and cleaned, reinstalled and I’m trying to start her back up. I get fuel up to the TBI but only when I manually prime the TMI will it start. Plus it stops running after about 10sec. I can step on the gas pedal and watch the fuel come out the injectors but after 10 sec something shuts it down???? I’m at a loss. Can any one help??
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Old 03-26-2022, 06:55 AM   #2
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The fuel pump power is controlled by the oil pressure switch and relay. There is a 10 sec timer that will run the pump for 10 sec when the ignition is first turned on to prime the system. Once the engine starts, the oil pressure switch closes and supplies power to the fuel pump relay.
So you may have a defective oil pressure switch , broken wire , possibly a blown fuse or no oil pressure. The oil pressure switch is located on the lower left side of the engine. Most have 3 terminals on them.
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Old 03-26-2022, 12:03 PM   #3
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Agree. Check all of the wiring to (and from) the oil pressure switch. Depending on what you had to work on, and around the TBI and distributer. The wire connectors become brittle with age, and can come loose.
If you need a wiring diagram for the oil/fuel circuit, let me know. Have the factory service manuals.
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Old 03-26-2022, 02:26 PM   #4
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Thank you very much.

I just recently had to replace the oil pressure switch about 2 months ago it痴 odd that it would work just fine then not at all just because there was diesel put in the gas tank. I used a commercial gas pump to remove the diesel directly from the tank where the fill tube enters the gas tank underneath the MH. Then disconnected the fuel lines where they crossover from the main frame to the engine block and turned on the ignition to pump out the fuel lines. Then dropped a shoestring into the tank at the top while I had the fill tube removed to see how much fuel was in the tank. It came back out with hardly any markings of fuel so I put the fill tube and fuel lines back together and out 20 gallons of premium gas into the tank and tried starting it. It wouldn稚 start unless I primed it as would only run for about 10 sec. The fuel pump does turn on with the key and sprays out the fuel lines where they connect to the TBI. I値l check the fuses and I知 fairly familiar with the wiring so I値l trace it and look for broken wires somewhere. If nothing else I値l replace the OPS again and see if that does the trick thank you for your insite
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Old 03-26-2022, 04:25 PM   #5
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Originally Posted by Jazzman112 View Post
It sits on a P30 chassis and Ihave been able to resolve the transmission issues and she drives so much better. Until 5 days ago. I gave the fuel attendant $200 and told him regular unleaded please then went inside for some cold drinks and smokes. Upon return I jumped in the drivers seat and proceeded to drive away from the gas station. I made it 3 blocks before it died. I was half full of diesel. I was down to maybe 5 gallons of gas when I stopped at the gas station. Long story short, everything has been taken out and cleaned, reinstalled and I知 trying to start her back up. I get fuel up to the TBI but only when I manually prime the TMI will it start. Plus it stops running after about 10sec. I can step on the gas pedal and watch the fuel come out the injectors but after 10 sec something shuts it down???? I知 at a loss. Can any one help??
I believe this is your switch and location





https://www.autozone.com/fuel-delivery/fuel-pump-relay
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Old 03-27-2022, 10:55 AM   #6
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There are two power sources for the fuel pump. One is the fuel pump relay, and the other is a special "hot fuel module". The relay kicks in when oil pressure is detected while the HFM is used to prime the system for approximately 20 seconds. It may be that your HFM is working but the fuel pump relay is not, or the oil pressure switch is not working.

There is one other possibility. I hate to mention it but it was the source of the exact same issue on my MH. The ECU it self may have failed since it's responsible for fuel pump relay control and injector pulses. Mine occurred when I had a surge during an electrical storm and the MH was plugged in without a surge protector. The engine would start and then shut down after a few seconds. After some time, it wouldn't start at all. No spray at the injectors even though I had fuel pressure at the inlet. Not saying that it's your problem, but it was mine.

One suggestion is to verify you have fuel pressure at the TBI inlet when cranking. If the fuel pressure drops off after 15 to 20 seconds, then it's the fuel pump relay or oil pressure switch related. If you have good fuel pressure but no TBI injection, then it may be the ECU or the ignition pulse detector related.
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Old 03-27-2022, 07:06 PM   #7
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The fuel pressure regulator is built into the TBI body as well, but it can be separately removed and replaced with the TBI body installed. It's easy to remove and replace it without any special tools.

If the pump is running but the fuel pressure is lower than it's supposed to be at light loads, it can be the pump or the regulator. For ours, it was the latter. A local shop rebuilt it at a fraction of the cost of a new one.
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Old 04-09-2022, 10:30 PM   #8
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The Ignition control module must be working for the injectors to fire (pulse).
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Old 04-11-2022, 10:54 AM   #9
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The Ignition control module must be working for the injectors to fire (pulse).
Yep, ECU needs to see ignition pulses in order to fire the injectors. In my case the ECU crapped out along with the ignition control module due to a lightening strike that took out those and the surge suppressor.
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Old 04-13-2022, 05:40 AM   #10
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You need a pressure gauge to put inline where the fuel line enters the TBI unit. You could have pressure but not enough to open the injectors. Possibly a defective fuel pump damaged by the diesel fuel in the tank or a clogged filter on the pump. Make sure the ground wire on the pump is in good condition and properly grounded. Also be sure any connections to the pump are clean and tight with no bent or missing pins or terminals.
To assure you are getting pulse to the injectors there are little neon lights available called "Noid Lights" which will plug into the wiring connector on the injectors in the TBI unit. If you have pulse the light will flash as the engine is turning over with the starter. If the light doesn't flash you have something electronically wrong in the system. Possibly a wiring issue or an ignition module or pick up coil in the distributor or even a blown fuse.
The "Noid Lights" are available from most automotive parts stores. There are a few different designs specific for different injection systems. All the TBI systems use the same light. These lights are reasonably priced.
When power is applied to the injector it simply allows the injector to open. The injectors rely on fuel pressure to open. That is why you need to be sure the pressure is within specs.
Another area of concern would be the Throttle position sensor (TPS) on the side of the TBI unit. This can be checked for voltage output with a scan tool easily with the scan tool's data screen.
If you have the vehicle shop manual there should be a "Trouble Tree" in the manual which will go through the test procedure step by step.
The oil pressure switch could be defective but it would be strange it would fail at the same time the diesel fuel was put into the tank.
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Old 04-17-2022, 08:11 PM   #11
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Curious...

What lead you to believe diesel had been put in given you didn't witness it?
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