I am having some problems with my 86. It starts but stumbles when I give it gas. I am thinking fuel pump but I have injector question. Should the injectors be able to spin/turn? I smell gas at the #7 injector and there is a puddle of oil/gas on the intake. the injectors spin and turn. the car will start but I can't rev it, it cuts out when I give it gas. I just need a place to start

 

When you open the throttle, the engine vacuum signals the FPR to increase fuel pressure.
This extra fuel mixed with extra air accelerates the engine.

I'd hook up a fuel pressure gauge to observe the pressure increase.
35psi @ idle, 42psi when opening the throttle.
Leaking o-rings at the injectors is a problem that should be fixed ASAP.
Observing any fuel in the vacuum line to the FPR, signifies a cracked FPR diaphragm. This is also an ASAP repair.

Oh yeah and there are a host of other parts problems that can be the culprit. I'm sure many CF'rs will chime in soon.

For now this should be a good place to start your troubleshooting.

 

Yes, you can spin the injectors. But it isn't good to do that as it can damage the o-rings. Where is the puddle of gas at?

I'd also get a scanner to scans to see if that would show up anything.

 

The vacuum signal only raises the fuel pressure 5 pounds. It ensures that you have a more atomized spray pattern at the injectors because there is less time for the engine to digest the fuel. The injectors don't increase and spray more fuel.
The reason your engine accelerates is because you have opened the throttle, and the computer gets the signal from the throttle position sensor that you require higher RPM or wish to maintain speed on a hill. The manifold temp sensor is modifying the map/mas signal to indicate the amount of air entering the engine.
The distributor tells the computer that you have either maintained or increased RPM.
A Mas air flow sensor is basically a hot wire that is being cooled by the incoming air, and the electronics on the MAF increase the voltage to the hot wire, and measure the resistance through the wire modifying the voltage to the computer based on the rate of cooling, interpreting the resistance/voltage as airflow.
A MAP measures vacuum which is a direct relationship to the throttle blades vs. work being done by the engine... Wider opening of the throttle blades indicate the amount of engine work being done by interpreting voltage from the throttle position sensor and the voltage from the MAP sensor as a signal that is modifying the computer information because less work done is more vacuum, and more work is less vacuum, ie; more or less fuel needed.
The oxygen sensor refines the fuel mixture by sending a voltage to the computer to modify the mixture by either varying the length of time the injectors are open, or opening them more frequently, or both.
The vehicle speed sensor tells the computer that the vehicle is in motion, and if the speed increased or decreased per the throttle position at the same time that the distributor is reporting engine RPM. The switch on the shifter tells the computer that the engine is in gear.
While the distributor is reporting, the computer is monitoring the timing of the engine via the distributor module, and controlling the esc, while listening to the knock sensor. All the while, the oxygen sensor is reporting fuel mixture to the computer and the injectors are opening and closing, metering the fuel based on all the other parameters.....


If you give it throttle, and the engine quits, the throttle position sensor is telling the computer to give more fuel, and the fuel isn't there.
Check fuel pressure, fuel filter, fuses on the injector drivers, fuel pump fuse, fuel pump relay and the fuel pump switch on the oil system at the back of the block.

Note:
I had a fuel pump go out, and had similar indications that you have, and it is possible for the injectors to work on 23 PSI of fuel pressure, although the engine hardly runs, because that's what I found when troubleshooting.

 

Coupeguy2001

Thank you for your detailed post. Lots of times I very little about how are cars work. Just enough to get in trouble. I look for your posts. I learn something every time I read your posts. This post really clarifed alot on how my car works.

Thanks
Mike.

 

Thanks Mike, I appreciate your appreciation

 

wow, great info. I appreciate the time you took to type it all down. Thank you. I am proceeding as advised. I recently had timing, cap, rotor,coil, tps, IAC, plugs all done so I am going through to make sure everything looks good and hoping for something stupid. just bought a gauge to test fuel pressure. don't know how to use a scantool or voltmeter/ohmeter but I guess I will be learning soon. FSM guides you through the diagnostics but it assumes you know how to use the tools. I am going to search the forum for this info. Thanks again, wish I had something more to send you

 

coupeguy, I just read your post for the 3rd time and it all clicked. I actually think I get it. I can do this. thanks man

 

one more thing to add. While searching the forum I saw some threads about "burping" radiator. I drained all the coolant when I took off the valve covers to paint them. All I did was fill the radiator and the recovery tank back up. Drove the car for a couple weeks and kept checking the coolant level and added as needed. The low coolant light never came. Don't know if this has much to do with my current problem but some have advised to check coolant level. Since I never purged the system, could this be another thing contributing to my current problems? thanks

 

Burping the radiator would only affect cooling, and if there was no water flowing past the computer temp sensor at the front of the manifold near the thermostat, the reference temp that the computer needs to go into closed loop would not be accurate. Otherwise, being in open loop, it would act as it usually does before warming up.
If not enough water in the system, it would over heat, surely sending it into closed loop. Since you have neither of those, I would say your cooling system is not a factor.

FYI,
THe coolant sensor is a flat metal piece that gets a ground through the coolant. When it loses the ground, it unbiases a transistor, and the light comes on. When the ground returns, the transistor turns off the light.

 

yeah, I didn't think it would cause my current problem but collectively all my rookie wrenching is starting to back up on me. Damn, I wish you lived in CT. Thanks again for all the info-E

 

I just bought a fuel pressure gauge and hooked it up on the fuel rail valve. when I turn the key it shows 3psi. I can't get the car to start so I don't know if it will go up. The car wants to start, almost starts but it seems like no gas. some gas did come out at the shrader valve and through the hose on the pressure gauge. I can also hear the fuel pump for a couple of seconds when I turn the key on. The injector fuses are good. Since I can hear the fuel pump but get no pressure does this indicate a bad pump? I want to check the fp relay, I just don't know how to. I have a voltometer and test light just don't how to use. I am sorry to impose but if anyone can give me a quick basic understanding of electrical testing hopefully I can stop bothering you guys and become a little more self sufficient/competent. Thanks

 

The first thing I would do is change the fuel filter. Then that item is right out of the picture. After that I'm not sure whether to check the fuel regulator of the fuel pump first.

 

I did change the fuel filter about 6k miles ago. It's cheap, easy to do and can't hurt I guess. I have the fsm and I would like to progress through the diagnostic steps. They tell you what tools you need but not how to use them. Anybody know of any threads or sites that give you a good idea of how to use the electrical diagnosis tools, ohms, volts amp etc. I think I know where and what but not how. Thanks

 

My money is on a ruptured pulsator in the tank.

 

I think I am going to change the fuel pump and sending unit, although I wish I could properly diagnose this so I don't stupidly replace parts. Is the pulsator part of the sending unit or fuel pump?

 

Some guys replace the pulsator with a piece of fuel injection hose.

 

Pulsator is between the pump and the metal fuel line in the sender. Replace with a piece of fuel injection hose double clamped on each end

 

Any special type of clamp needed? Or just any small heater hose clamp?

 

replaced the fuel filter today to no avail. picked up a fuel pump at auto zone for $50. putting in tomorrow to see what happens