Fuel Pump Relay Diagnostics?

[Banshee365]

Hey guy's. I spent the $15 for the 2-day subscription to the techinfo site and downloaded all of the manuals. One problem with doing that is most of the links in each document do not lead to a file that is not in the same folder as that page is. I've got alot of problems such as high idle, running very rich, hard to start when warm, smells like rotten eggs, etc... and the Diagnostic section in the manuals points to fuel pump circuit problems as well as others. I cannot find the fuel pump relay diagnostic manual with the page (SF-54) and I also can't find (SF-53).

Does anyone here have these pages? I also have a P0115 coolant temp sensor circuit malfunciton CEL code along with all of these problems, even after I installed a new sensor. I'm torn between having fuel issues, or the ECU. autoecu.com in Tennessee say's they'll check the ECU for $55 for problems in the circuits.

The car runs fine when cold for the first few minutes then starts idling really high and running really rich. It idles between 1,200-2,400 rpm out of gear. It's crazy. Any ideas? I'd like to troubleshoot the fuel pump relay and make sure the fuel system is working properly.

[curiousB]

Maybe use your PC search command at the directory where all these pdfs reside and search for a few key words in the documents fuel pump diagram, fuel pump relay, fuel pump replacement

This may lead you to a smaller set of PDFs to look through.

[curiousB]

On second read its hard to fathom how a faulty pump would cause high idling? I would think a faulty pump would starve the system for fuel and result in loss of power. Maybe fuel pressure is too high but that wouldn't be the pump rather the fuel pressure regulator.

Sound more like dirty throttle plate and or faulty IACV to me.

[Banshee365]

I could see those being issues as far as the high idling goes. What about the running really really rich and being hard to start when warm? Smells like rotten eggs too. And the CEL for engine coolant temp circuit manfunction even with a brand new sensor. Should I start suspecting the ECU?

[curiousB]

I would have ECU down the list in priority. Why are you sure its running rich (once fully warmed up)? You gas mileage would be poor if you are so if you check mileage next tank compared to typical that may confirm it. If its running rich the it could be O2 sensors. If they are faulty the ECU goes into open loop mode where it intentionally runs rich rather than lean and power starved. The ECU would have error codes in the log if this were the case so a code reader may be handy.

I'd check for ECU codes as first step. If you have O2 sensor errors address them. If no ECU code then I'd do a throttle body (including MAF sensor) and IACV cleaning as its a good thing to do routinely so you're not wasting time.

Not sure about temp sensor issue. If your put in a new sensor maybe connector is corroded or a wire is broken?

[Banshee365]

I do not have any current o2 sensor codes. Only the coolant temp circuit malfunction. The car will no drive reliably enough to leave my driveway without it shutting down, flooding out, and not restarting until it sits long enough to finally crank up and blow black smoke out the back. That's why I think it's running rich. I wish there was a light (no trac control) on this car that would indicate it's operating in limp mode. The car will also hesitate off idle when you rev it, even at 1,200 rpm idle. That's another indication to me it's running rich. It does all this while smelling like rotten eggs. I can't afford to go replacing $300-$400 in o2 sensors just in case they might be bad. I've cleaned the throttle body recently and cleaned and checked the operation of the IACV. The IACV on the '96 does not come apart like the Gen 1's so all you can do is cleaned the plunger with some carb cleaner and a wire brush attatchment on a drill. What's triggering my suspision of the ECU is the intermittent coolant temp circuit malfunction CEL that cannot be duplicated by wiggling wires and such over the sensor. This thing is driving me nutty!

[curiousB]

OK well this is pretty serious malfuntion then.

Temp sensor good vs bad wouldn't result in such extereme behaviour. Could be MAF sensor faulty causing improper drive of fuel injectors. That would have a code in the ECU though and since you said you didn't have O2 codes I assume you check for all error conditions.

Are you sure its fuel? Could it be one of the distributors is faulty and you only have 4 cyclinder running? You didn't mention year and model you have.

[Banshee365]

it's a '96 LS with 203k. New plugs, wires, caps, rotors.

Never a code for the MAF. Had an intermittent code for an o2 sensor but it hasn't come back. Could I unplug the MAF and see how it runs? Some say their car runs better with it unplugged if it's bad. I could at least do that to maybe troubleshoot it and replace it if it's bad. The car is running soo horrible. The idle is just out of control then it starts running really rich. How can I tell if it's running in limp mode? When it's running all 8 cylinders fire fine. It just idles super duper high then starts running rich to where when you shut it down it won't start back up until it cools. I'm so stumped.

[curiousB]

Does it ever ride well (ie once warmed up, or only when cool)? It sounds like its full time running poorly.

The MAF sensor is a central element to the fuel injection system. If it is faulty you either won’t run at all or in a very poor manner (limp mode). The ECU would have a code denoting this so it doesn’t seem likely.

This is why I suspect ignition. Even a bad O2 sensor wouldn’t make car run this poorly. If it where fuel injection there are numerous codes that could pop up.

What is relationship between new plugs, caps and rotors and this problem come on the scene? Sorry to ask but could you have miss wired some of the plug wires? Maybe a bad plug or two? You might want to search on this forum for distributor problems in this car. There are many threads about ½ car going dead and running on 4 cylinders. The engine runs but very rough. Sounds a bit like your symptoms.

[Banshee365]

I installed the plugs, caps, rotors, and wires about 2 years ago. It ran fine until now. When it's running all cylinders are firing. It smells like rotten eggs after it's flooded out and you can finally get it started after it sits for a while. It seems to be strictly a fuel metering issue since the ignition fires fine when the engine is running. Even up to high revs, it's smoth as can be. I had the car hooked up to a snap-on scanner a few weeks ago and it wasn't showing a single bit of misfiring. If it wasn't for the coolant temp circuit malfunction CEL i wouldn't blame the ECU for anything. But with a new sensor and a good harness even the factory manuals say to replace the ECU. If the CEL wasn't there I would look more at the MAF sensor and o2 sensors. I'm guessing it's one of those 3 that's messing things up.

Are the 96 models also effected by the trunk wiring harness?

[curiousB]

I installed the plugs, caps, rotors, and wires about 2 years ago. It ran fine until now. When it's running all cylinders are firing. >>>> Are you sure there isn’t some intermittent maybe on the ignition coil for one side that works and doesn’t work. A faulty coil that heats up and starts failing, corroded connector, or intermittent cable harness.<<<<

It smells like rotten eggs after it's flooded out and you can finally get it started after it sits for a while.

It seems to be strictly a fuel metering issue since the ignition fires fine when the engine is running. Even up to high revs, it's smooth as can be. >>>> Are you sure this is true? Fuel left in cylinder unfired (due to missing spark) will end up in exhaust and burn there creating odor, smoke, and jerky performance.<<<<

I had the car hooked up to a snap-on scanner a few weeks ago and it wasn't showing a single bit of misfiring.>>>> yes but was it running poorly at the time or running OK? If you have an intermittent electrical problem (causing one bank of distributor to go dead) but you measured when the intermittent was OK then the scanner didn’t tell you much. If the car was laboring like you’ve seen but the scan showed good spark on all cylinders then yes I would then be more inclined to think fuel metering. Maybe a stuck open injector that is leaking all the time (doesn’t shut off). ECU can’t detect a stuck open injector. Emissions will surely fail though.<<<<

If it wasn't for the coolant temp circuit malfunction CEL I wouldn't blame the ECU for anything. But with a new sensor and a good harness even the factory manuals say to replace the ECU. If the CEL wasn't there I would look more at the MAF sensor and o2 sensors. I'm guessing it's one of those 3 that's messing things up. >>>> This is the mystery, if the MAF and O2 sensors were faulty you’d have error codes on them. Since you don’t it seems less likely they’re faulty.<<<<

>>>>Hey it could be the ECU. It’s just that at the root of it an ECU is a microcontroller with memory and I/O. If it were to be faulty I would expect it to be either completely dysfunctional (full failure of microprocessor subsystem), OR healthy enough to log some error codes to give you clues. It seems to be neither which leads me to think the ECU is possibly OK. I tend to think wiring and sensors are far more likely to hard fail before an ECU. Lastly the ECU is pricey so its obviously better if it isn’t the problem from a wallet perspective<<<<

Are the 96 models also effected by the trunk wiring harness? >>> Not sure about this. I thought that was earlier models but seems pretty easy to go check.<<<<