(NOT) driving me nutz

[ocrick]

My 89 coupe has developed a new trick. It will drive just fine all day and in the early evening I will park for @ 20min. When restarted it runs like #$%#!!! Rough idle, won't go over @ 800 rpm and will die in about a block and can't be restarted.

At first, cleaning the contacts on the crank fuse (underhood) got it started. The next time I had to jump 12v from the battery to the fuel pump relay socket to get it started. The service engine light came on while it was dying but no codes were stored???

Today I replaced the MAF, Burn off and FP relays and cleaned the contacts at the body harness to the fuel sending unit. What else can do?? :bash

 

[Vette_Newb]

Fuel filters? I had an Rx7 that would do crazy stuff like that when the inline filter was bad.

 

[vettenick]

Assuming that your charging system is OK and that all of your power and ground connections are good (including the battery cables):
Basically, there's two thing to check: spark and fuel. The next time she acts up, disconnect one of the plug wires, put a screw driver into the terminal and hold the shaft end about one inch from a good metal surface. Crank the car to see if the ignition system can generate sufficient spark. If it can't, you could have a coil that's shorting internally or an ignition module that's crapping out when heat soaked.
On the fuel end, hook up a fuel pressure gauge,tape it to the windshield and drive the car to see if fuel pressure is OK. This you can do before the car acts up. You'll be surprised what you'll find on some cars that even appear to be OK.
If the above two checks reveal nothing, then I would check fuel injector operation/resistance when the car acts up. Again, injectors can short internally when hot.

I hope this helps.

 

[ocrick]

Appreciate the suggestions. I have been working on a small idle "lump" for the last few months. I have replaced plugs, wires, coil rotor and cap.

I have also had some long crank (hot) starting so I have checked the injectors. They are all within 1 ohm and I used an OTC injector tester to do both load and flow tests. Both were within specification.

In setting up the flow test cycling the key only provided about 38psi. Today I pulled a vacuum on the line to the pressure regulator so the diaphram appears ok.

When the car does it's little "trick" there is no fuel pressure. Can't hear the pump running either.

The problem is that the normal start sequence is for the ECM to provide 12v to the pump for 2 seconds to pressurize the fuel rail....after that the ECM looks for an RPM signal about say 300 to indicate the engine has started. I assume that once the engine has started the ECM again supplies 12v to the pump.

My symptoms almost feel like a low or variable voltage is sent to the pump. The car does "run" for a while. The other interesting thing is if the engine is running (with oil pressure) it should be able to run anyway....mine dies.

I am beginning to think either the ECM has some dead functions or the pump is going south.

 

[69MyWay]

I fought some crazy hard start problems on my 85.

It would only start and run decent if I restarted it within minutes of shut down. Otherwise, it struggled.

Come to find out, the fuel pump check valve had failed It would put out decent pressure, but as soon as you turned the car off, all the fuel would run backwards through the feed line right through the pump....bypassing the regulator on the rail.

This was causing a starve problem to the injectors and a terrible balance problem with pressure.

I had replaced the regulator, injector test...etc....... and only after changing the pump, was the problem solved.

This is the first time I ever ran into this problem...and it sounds very much like yours.

Good luck!

 

[vettenick]

Sounds like you've done your homework. Next time it acts up, jump power to the pump at the relay. In other words, bypass the relay. If you don't hear the pump run, then either the pump is bad, or you have a bad connection at the pump. Sometimes, if you give the bottom of the fuel tank a light rap with your hand you can get the pump running again. If that's the case, then it's pump replacement time.
The pump impeller is actually ceramic with tight tolerances, sometimes a small piece of debris will get in there and jamb things up. If that's the case, then you must clean out your tank, otherwise the new pump will suffer the same fate.
If the pump runs OK, then you need to find out why the ECM is not giving the fuel pump its wake up call. Independent of that, if you crank the car long enough to build up oil pressure, the pump should get power through the oil pressure switch.

 

[ocrick]

Well....here is my plan for tomorrow morning. First, I will pull out the battery and clean and tighten the ECM ground wire which is behind it. Second, I will disconnect the ECM and use some electrical contact cleaner on the terminals.

After putting it all back together, I will start it up and pull off the TPS connector until it throws a code. Then key off, hook up the old scanner and see if the ECM has a code 22 in memory....if not it's ECM ordering time. If it does hold the code then ???

Either way I think I will up the priority on fuel pump sock and filter replacement to get a little better fuel pressure.

At least I won't get in trouble by havin too much free time!

:J

 

[ocrick]

UPDATE - the ECM and grounds are clean, tight and appear to be working. I was able to set hold and erase a code 22 (TPS open circuit).

Well...it now has a fresh set of relays,ectors cleaned connectors at the sending unit and the ECM. Next weekend I plan to change the fuel filter (although my no start is electrical) and possibly later to install a new pump.

Anybody running Walbro? Is it a direct drop in?

 

[oldace84]

Leaking injectors?
Maybe.
Good Luck
tony