TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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Hi,
I have a 83 Trans am with crossfire injection on a 305. It has a very fluctuating idle, it idles high, then basically dies. When you hit the gas it seems to be not burning gas, as it bogs and then all the sudden kicks in after about a 2-3 second delay. Someone told me that the catalytic converter may be plugged or old. Here are a few things i was thinking it could be:
Fuel pump
Firing order
Timing
injectors?
I can post a video too if you want to see it for yourself.
Any info would be appreciated!
Hey, there! I have been playing around with my Crossfire car for a little over a year. Lets see if we can get you running.
On the "bog", right after you press on the gas, does the engine go silent before it kicks in, or does it stumble around before kicking in? If the first, could be fuel delivery related. Have you replaced the fuel filter? Do you know what your current fuel pressure is? I found it really hard to diagnose problems without knowing fuel pressure. I would highly recommend that you get a fuel pressure gauge.
If the second, your engine may be loading up with fuel. A bog can occur after you press the throttle when an engine has loaded up with fuel (i.e., running very rich). The engine will bog and stumble while it tries to clear the excess fuel out and then kicks in after it has done so.
Does the car accelerate ok, either from a standstill or on the highway? If so, probably not the cat. Does the exhaust make a real loud whooshing noise? That usually indicates a stopped up exhaust.
Firing order is easy enough to check.
Timing is easy to check. In case you did not know, the EST bypass wire on a CFI car is behind the passenger side valve cover. Need to disconnect the ECM from the distributor via the EST bypass before you check the timing and then reconnect it afterwards. Other than that, checking timing is no different than a non-computer controlled car.
Injectors - take the air filter assembly off. Watch the injectors shoot fuel into the engine. Is the fuel a fine mist (good) or is it coming out in a stream (bad)? Large droplets are generally are not good.
Are all of the parts on the engine original? An erratic idle can be caused by worn out throttle shaft bushings. Your throttle bodies may need to be rebuilt. I thought I read that an EGR valve stuck in the open position can cause an erratic idle as well.
One other thing I highly recommend you do is replace all of the rubber vacuum lines connected to the engine if your lines are originals. Don't forget the small rubber hose at the vacuum modulator on the passenger side of the tranny (the last piece of hose I replaced and the source of my leak).
__________________ Relatively original 1982 Z-28 with Crossfire, T-tops, and A/C delete.
Engine mods: 355 cid, Edelbrock Performer AL heads, Renegade cross-ram intake, COMP 249XE cam, 65# injectors, 2.0-inch throttle bodies, EBL Flash computer, complete MSD ignition system, K&N air filters, Hooker shorty headers and y-pipe, Edelbrock cat-back exhaust system, TCI Street Fighter TH-350, TCI 2200 RPM stall converter, 3.73 gears in stock posi rear end, SSBC two piston aluminum front calipers.
Hey,
thank you for your reply, It seems to surge forward on the idle, it also stumbles when shifting into gear and when it starts moving. Another thing is when you speed up a little faster it will literally go like 10 miles an hour and suddenly kick in. I really hope its something simple. I'm used to carburetor engines so how do I lean it out?
Thanks again
If the engine is stock and in decent condition, the tune should not need to be changed - i.e., changing the tune would just be fixing the symptom of a problem and not the problem itself.
Do you have the ability to check error codes? Need to see if the computer is throwing any codes and start there. Also, a Chiltons, or even better, a factory service manual, would be very helpul. You can get a factory service manual on ebay.
Another problem that can cause a rich condition is a bad coolant temperature sensor (CTS). If your CTS is bad, it could be tricking the ECM to think that the engine temp is colder than it really is. The ECM adds fuel to the base tune when the engine is cold (like a choke). These are fairly cheap, so you might try replacing it and see if it helps. Without the ability to read computer output, you are really shooting in the dark in diagnosing problems.
To test for worn throttle shafts - with the air filter assembly off, wiggle the throttle shaft where it goes into the throttle body. If the idle moves without you actually opening the throttle, then you have worn out throttle shafts.
__________________ Relatively original 1982 Z-28 with Crossfire, T-tops, and A/C delete.
Engine mods: 355 cid, Edelbrock Performer AL heads, Renegade cross-ram intake, COMP 249XE cam, 65# injectors, 2.0-inch throttle bodies, EBL Flash computer, complete MSD ignition system, K&N air filters, Hooker shorty headers and y-pipe, Edelbrock cat-back exhaust system, TCI Street Fighter TH-350, TCI 2200 RPM stall converter, 3.73 gears in stock posi rear end, SSBC two piston aluminum front calipers.
the problem is your throttle body shafts have worn and have created a vaccum leak, also your vaccum lines may need replacing. Your tb's have to be in a perfect syncronization as well to perform correctly.
I would pull the intake and have the throttle bodies rebushed, clean the intake out because fuel tends to pile up ina sludgy form on the bottome. Install with new gaskets and syncronize your your tb's. Joshua
Well It Cant Be That Cuz I Got Them Rebushed Wen i Got The New Engine... But Im Thinking that they might not be synchronized... and probably a vaccum lines . but they are already rebushed
I ended up replacing all of the vacuum lines - and I mean all of them. Also replaced the Map sensor, the EGR valve, the temp sender, the thermo vac switch, the fuel filter, the O2 sensor, and the ecm, made sure the throttle position sensor was adjusted correctly and made sure the IACs were cycling properly.
I put in a new distributor pick up, distributor module, cap, rotor, plugs, and wires.
My CFI went from running just like yours to running excellent.
I never had any codes thrown before I made these changes, but these cars are almost 30 years old, these parts just weren't made to last for ever. The entire overhaul worked great, even if it was overkill.
I never rebushed the TBIs.
Fuel pressure must be read between the two TBIs on CFI. Anything less that 12 psi is going to cause problems.
I am now down to 6 psi and it is beginning to affect the performance. Will be replacing with the TPI motor pump over the winter.
Once again, maybe what I did was overkill, but the car really does run exceptionally well for such a maligned design.
If you really just want to get to a point that the car works as intended, I would strongly recommend a comprehensive approach similar to my crazy azzed job.
Wow haha Serious Overkill
But Im Thinking that im gona do that to mine too
it just gets on my nerves that it wont run right.
it bogs down wen hot but if i leave it over night and run it in the morning it runs good but wen it warms up it runs like crap
Re: CFI Bogging and irregular idle
Hey, there! I have been playing around with my Crossfire car for a little over a year. Lets see if we can get you running.
On the "bog", right after you press on the gas, does the engine go silent before it kicks in, or does it stumble around before kicking in? If the first, could be fuel delivery related. Have you replaced the fuel filter? Do you know what your current fuel pressure is? I found it really hard to diagnose problems without knowing fuel pressure. I would highly recommend that you get a fuel pressure gauge.
If the second, your engine may be loading up with fuel. A bog can occur after you press the throttle when an engine has loaded up with fuel (i.e., running very rich). The engine will bog and stumble while it tries to clear the excess fuel out and then kicks in after it has done so.
Does the car accelerate ok, either from a standstill or on the highway? If so, probably not the cat. Does the exhaust make a real loud whooshing noise? That usually indicates a stopped up exhaust.
Firing order is easy enough to check.
Timing is easy to check. In case you did not know, the EST bypass wire on a CFI car is behind the passenger side valve cover. Need to disconnect the ECM from the distributor via the EST bypass before you check the timing and then reconnect it afterwards. Other than that, checking timing is no different than a non-computer controlled car.
Injectors - take the air filter assembly off. Watch the injectors shoot fuel into the engine. Is the fuel a fine mist (good) or is it coming out in a stream (bad)? Large droplets are generally are not good.
Are all of the parts on the engine original? An erratic idle can be caused by worn out throttle shaft bushings. Your throttle bodies may need to be rebuilt. I thought I read that an EGR valve stuck in the open position can cause an erratic idle as well.
One other thing I highly recommend you do is replace all of the rubber vacuum lines connected to the engine if your lines are originals. Don't forget the small rubber hose at the vacuum modulator on the passenger side of the tranny (the last piece of hose I replaced and the source of my leak).
good write
Last edited by Javier; 01-13-2011 at 01:39 AM.
Reason: error
