Help! Crossfire EFI problems.

[Shane]

Ok, I'm having issues with stalling, sputtering and extreme difficulty starting with my 84 Vette when the motor is at operating temp(above 160f).
I have checked and/or changed all sensors and vacuum lines.Many I have asked say vapor lock, yet being fuel injection, I don't think this is the issue? I've also considered Fuel pressure or something with the distributor(though it doesn't seem to be misfiring)

I'm completely lost. Please help!

 

[boomdriver]

CFs seem to be very sensitive to the temp sensor working right. The fuel pressure is only 15 psi...so thats easy to get to if the filter is decent.

If the inj are clean, and you have good flow, I'd go to the EGR and see if thats sticking open. A vac leak is still possible.

 

[xfirez51]

You swapped the CTS sensor at the front of the manifold?

 

[Shane]

You swapped the CTS sensor at the front of the manifold?

Yup.

 

[Shane]

CFs seem to be very sensitive to the temp sensor working right. The fuel pressure is only 15 psi...so thats easy to get to if the filter is decent.

If the inj are clean, and you have good flow, I'd go to the EGR and see if thats sticking open. A vac leak is still possible.

Know what? i didn't even think about that.(EGR) I'll check it out. Thanks.

 

[xfirez51]

160d F is about where motor goes Closed Loop. I'm assuming O2 sensor has been changed.How many miles on car? Have u timed it recently?

 

[Shane]

160d F is about where motor goes Closed Loop. I'm assuming O2 sensor has been changed.How many miles on car? Have u timed it recently?

97k miles. timing has been adjusted recently, in an attempt to fix the problem, and O2 sensor was changed.

 

[xfirez51]

I bring up the timing because at 97k miles, I would expect to see an issue w the 2 piece balancer. The outer hub moves in respect to the crank giving you a false reading. I installed a Fluidamper. Just a thought. You can mark the inner and outer hubs then start the motor. Put timing light on it and see if it's still lined up.

 

[nelson84]

On my crossfire I have my timing set at 12.

 

[vetteboy86]

Does the motor run fine, and start fine when cold, when in open loop? My thoughts are that if the motor only runs poorly once closed loop occurs, their could be a problem with engine management as the ECM see's it. Hence the suggestions about checking the inputs (sensors) to the ECM.

Do you have a FSM (Factory service Manual). This would provide excellent trouble shooting procedures.

 

[Shane]

Does the motor run fine, and start fine when cold, when in open loop? My thoughts are that if the motor only runs poorly once closed loop occurs, their could be a problem with engine management as the ECM see's it. Hence the suggestions about checking the inputs (sensors) to the ECM.

Do you have a FSM (Factory service Manual). This would provide excellent trouble shooting procedures.

I do not have an FSM. It starts fine when cold, idles roughly,then smooths out after warming up a bit. The real issues happen when its at operating temps. It sometimes stalls and is extremely difficult to to restart when the motors hot. After it cools down it fires up just fine. The check engine light isnt on and its not throwing any codes.

 

[xfirez51]

Have you checked the underside of the oil cap? Does it look frothy?

 

[Shane]

Have you checked the underside of the oil cap? Does it look frothy?

I have. No it doesn't.

why?

However, I am now noticing some smoke coming up from behind the motor, but this appears to be an exhaust leak as it doesn't smell like anything is burning. I know next to nothing about these crossfires. All sensors, TBI units, gaskets, etc where replaced by the previous owner or myself.(I have receipts for the work done prior to my ownership) I'm trying to avoid going to a mechanic,but it seems like i may not have much of a choice.

 

[boomdriver]

Has anyone looked at the coolant temp sensor? or run a scan to see what the ECM is seeing? sometimes that alone is very enlightening. The ECM might be seeing something totally different that what you see on the display.

Those temp sensors seem to be a critical part of the ECMs data stream for proper operation on CFs.


*********I see that I ask about this earlier...sorry.. One track mind. *******

Next time after driving with the misfiring and bad behavior, pull a spark plug and see what that says...if its dark or wet that could indicate fuel, too much to burn well. The ECM may not know that the eng is up to normal op temps and keeps sending extra fuel as if it were stone cold. Thats a misfire for sure...

Same plug condition, different cause, worn fuel inj thats leaking or dripping fuel instead of spraying and atomizing.

 

[xfirez51]

Yes pull the plugs. See if anything is happening there. Do any of them
look like they've been steam cleaned.

 

[ex-x-fire]

Did you change the coolant temp sensor? If you did, did you use an oem style? Those are troublesome, use one from a 88-up tbi truck(get the connector too). There are other cars that use that sensor, the parts store should have the connector too.
Check that fuel pressure at the fuel filter. Theres a rubber hose connection that you can tee into.

 

[geekinavette]

If you still want to try to save this thing...I have a couple of thoughts....

First observe the fuel spray pattern from the injectors when it is running well, and compare that to when it starts running poorly. It should be a nice even conical-shaped spray pattern. You can even listen to the injectors, notice if the audible pattern starts becoming erratic. KEEP YOUR FACE AWAY FROM THE INJECTORS! If that thing backfires even a little...it will come right up out of the throttle bodies, you don't want to be anywhere near the injectors if that happens. View the spray pattern from the side of the car.

If one starts acting up but the other looks ok then there is some problem with either that injector or the driving circuit for it. Could be anything from a loose connector, leaking injector seals, bad injector or a failing ECM driver circuit (it does happen).

Also observe the injectors after you shut the engine off (after it starts acting up). If there is ANY fuel dripping from either injector then it is time to replace the injector o-rings.

If they both seem to go into raging fits...you might have an ignition module (under distributor cap) that is failing when it gets hot, not super common but I have seen it happen. Another ignition system clue is if you had a timing light hooked up and the light strobe starts becoming erratic about the same time it starts running poorly. The reason this will affect the injector spray pattern is because the ECM uses the distributor reference pulse (generated by the ignition module) as a trigger to fire the fuel injectors.

 

[Shane]

If you still want to try to save this thing...I have a couple of thoughts....

First observe the fuel spray pattern from the injectors when it is running well, and compare that to when it starts running poorly. It should be a nice even conical-shaped spray pattern. You can even listen to the injectors, notice if the audible pattern starts becoming erratic. KEEP YOUR FACE AWAY FROM THE INJECTORS! If that thing backfires even a little...it will come right up out of the throttle bodies, you don't want to be anywhere near the injectors if that happens. View the spray pattern from the side of the car.

If one starts acting up but the other looks ok then there is some problem with either that injector or the driving circuit for it. Could be anything from a loose connector, leaking injector seals, bad injector or a failing ECM driver circuit (it does happen).

Also observe the injectors after you shut the engine off (after it starts acting up). If there is ANY fuel dripping from either injector then it is time to replace the injector o-rings.

If they both seem to go into raging fits...you might have an ignition module (under distributor cap) that is failing when it gets hot, not super common but I have seen it happen. Another ignition system clue is if you had a timing light hooked up and the light strobe starts becoming erratic about the same time it starts running poorly. The reason this will affect the injector spray pattern is because the ECM uses the distributor reference pulse (generated by the ignition module) as a trigger to fire the fuel injectors.

Thanks for the info. I really would like to keep the CFI if possible, but i'm getting pretty frustrated. The injectors are brand new. You think it could be an ignition or ECM issue? Or timing for that matter? I do know that the previous owner had adjusted the timing in an attempt to solve the issue. What are the OEM (or ideal, if different from OEM) specs for the timing?

 

[geekinavette]

"Brand new" does not mean good! Don't make the assumption that because something is new means that it can't possibly be malfunctioning.

I wouldn't suspect the timing adjustment itself based on your symptoms. The factory setting is 6 degrees BTDC...and don't forget to disconnect the EST Bypass wire when checking/setting the timing. In fact, you can see if the poor running when hot problem persists with the EST disabled. Until this problem is identified and corrected I wouldn't deviate from the factory timing settings (assuming here that the engine and ECM are factory stock). It would also probably be a good idea to verify that your TDC mark on the balancer is in the correct position...by using the good 'ol "finger over spark plug hole and screwdriver" method to approximately find #1 compression stroke TDC and verify the balancer mark lines up with 0 on the timing tab.

Yes ignition and/or ECM driver problems can easily cause the symptoms you describe. As can leaky injectors, both as described in the previous post.

You're going to have to go at this systematically...pick a system to test/troubleshoot and eliminate one at a time. It is difficult to do under such frustration...believe me I know, been there many many times...but absolutely necessary regardless of the type of induction system (CFI, Carb...etc). Check the timing out as mentioned above, if that yields nothing obvious (and I suspect it won't, but anything's possible), then continue with the observations I mentioned in the previous post. These are not difficult to do and won't take a lot of time.

If you notice anything "unusual" with the timing, fuel spray pattern, or timing light operation...then move on to measuring engine vacuum. Check vacuum both running "normal" and running poorly as it heats up.

Report back with what you find after performing these tests.

 

[Shane]

I believe the problem has been solved. After a bit of work the car now runs pretty well. I replaced the plugs and wires,fuel pump,fuel filters and fuel lines(they didn't "look" like they needed it, but the fuel pressure was low and they were the factory parts, so pretty old) as well as the distributor cap and rotor, and had someone check and adjust the timing(as I don't own a timing light)and some tuning. I didn't identify the problem, but it's safe to assume it was one of these that have been replaced. Thanks to all of you who offered assistance. It's greatly appreciated.




Now it's time to start restoration on the interior and a nice paint job.