I have an 89 iroc with the 5.7 TPI. I have a problem with the fuel pump not pumping but it is intermittent and hard to recreate or diagnose. Sometimes I can drive for hours without it happening, there is no real pattern or consistency to it. I finally traced the wires and have found that the ECM is cutting power to the relay, hard confirm but I found the trigger wire and ran a jumper to the passenger seat and hooked up my multimeter to it and drove for an hour till it finally happened. Question is what could cause this, the computer possibly thinks the engine is not running?? and cuts the power to the fuel pump. Is there a sensor that could be bad causing this? In fact the car could run a hell of a lot better than it does and possibly the ECM itself is bad. I have in the short time I've owned the car replaced the plugs, wires, put in new fuel injectors and related gaskets, replaced the Fuel pressure regulator and EGR valve. These were not entirely to try to fix a problem, the injectors were bad and the FPR and EGR were because they are easy to get to when you've got all the stuff off. I am no longer in an "improvement" stage so throwing a lot of new sensors and parts blindly at it to try to solve the problem is not my first course of action. I also swapped a MAF off a friends who has the same car and that wasn't a contributing factor. He won't let me borrow his ECM unfortunately. Anyway the first problem is this fuel pump thing so any suggestions would be appreciated. The car is stock(I believe) the only thing that looks upgraded would be the ignition is accel.

 

Also to note: I am new to ThirdGens, TPI and computer controlled cars in general, always had 70's carburated models. But I'm not new to electronics or cars at all and know how to wire the relay to bypass the ECM if necessary, this is just my effort to find the real problem and correct it the right way. The more I pull away from stock the more I have to remember later.

Revision: I may be wrong about ECM, all I can say for sure is relay is not getting signal, but it may be something else. I have done more research and this fuel pump may be controlled by the oil pressure sensor and not the ECM at all except for a few seconds before start. I'll try to look into this if I can figure out how to test the idea.

 

Usually a fuse between the battery and the fender, in it's own weatherpack - a 20 amp fuse - that powers the ECM and powers the oil pressure sending unit (the OPSU will also run the fuel pump in the event that the ECM fails to - see if that fuse or it's holder has an issue - there will be one red wire running into it, and one orange wire running out of it, with fuse insude.

 

Only the ignition reference pulse would affect the ECM's control of the fuel pump.

 

I'm not entirely sure of that, from what I've found after creating this post the ECM only turns the pump on for about 2 or 3 seconds when the key is turned on to prime the line enough for start, after that the oil pressure sensor sends the signal to the pump to run when the oil sensor senses pressure; so if the car is in an accident, or rolls, or shuts off the lack of oil pressure would cause the fuel pump to shut down for safety reasons. This is sending me down a new path of testing now, but sadly my JOB keeps getting in the way. Don't they know I need a couple of days off to play with my car? Hate waiting for the weekend.

 

What you've found is wrong.

 

I talked myself in buying a new ecm to try that because of another problem, the new ecm solved this and 3 or 4 other problems also. So I guess this thread is done. Thanks everyone.

 

I know, old post, but what part is wrong? I have an 87 5.7 TPI and at least for my setup I thought that he was correct about his findings. Does the 89 have some changes or am I mistaken in my understanding?

 

The ECM powers the pump through the fuel pump relay as long as reference pulses are received from the distributor, which means as long as the engine is running.

Loss of oil pressure won't stop the engine. That's not even a desirable thing to have happen from a safety point of view. Imagine what happens when Joe Ignorant lets his oil level get low, then tries to merge onto the freeway.

Likewise, how could an OPSU be useful in stopping the engine in an accident? Oil pressure will only drop when the engine is stopped, so the engine has to be stopped before the OPSU can stop it.

 

I have been fighting the same problem for 4 weeks now.I am down to thinking its ECM related. I have put in a newfuel tank, fuel pump, fuel filter, TPS sensor, ECM temp sensor and pigtail,new fuel regulator, fuel rail seals, new upper and lower injector seals. When it is cold outside ( below 55 degrees) it will not start.I can hear the pump click on, but no pressure at the Shrader valve. Once the day warms up, it will start and start every time all day long and evening until the next morning. Yesterday morning, I put a small heater in the passenger floorboard for about 15 minutes. Got nice and warm and it fired right up. Did the same thing this morning. Could ambient temp really affect the ECM? Should I jsut replace the entire ECM? Still needing help guys. anything would be greatly appreciated.

 

86-87 have back-up power coming from the oil pressure switch directly to the pump. If the relay fails you can crank your engine enough to build oil pressure and run the fuel pump. I don't know about other years.

 

Same through 2001, and obviously not just on TPIs.

 

Apeiron and ACCLR8N, thanks for clarifying. After driving and working on this thing for thirteen years, there are STILL more things to learn.

 

Hello i am having the exact same problem with my 89 camaro. When i push the accelerator, it cuts out but instead of killing the engine, it just keeps going like normal. This problem has been getting worse and worse every day. When i slowly push the gas pedal, it doesn't do it. I am being told that it is the electrical harness to the pump is bad (defective) and that putting in a new one will fix it. Is this really the problem? I am feeling restricted because the car does this and am getting very peeved from it doing this. ANY help would be greatly appreciated.

 

Weak voltage could make it behave that way. In order of easiest to check: Fir I would measure voltage at the battery engine off should be 11-12V. With the engine running it should be about 14V at the battery.

Next I measure the fuel pressure. Should be at least 38psi idle and reving.

 

read thru these threads check the fuel diagnosis flow chart



http://forum.grumpysperformance.com/...php?f=32&t=596

http://forum.grumpysperformance.com/...php?f=80&t=728

http://forum.grumpysperformance.com/...hp?f=32&t=1401