TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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I have a 1991 RS that I've been trying to fix up, bought it for cheap from a friend who never really had the time to get it running. I'm not really looking into major performance mods (yet), I'm just a college student who wants a working car
Anyways, the engine runs decently, but very rich, I can see dark smoke coming from the exhaust and it smells heavily of fuel, makes a ton of smoke if I floor it.
The CEL is not on, and with my laptop hooked up running WinALDL all the sensor values seem normal, no error codes.
So far I've:
-Rebuilt the TBI unit with new fuel pressure regulator, gaskets, etc. and soaked the injectors in rubbing alcohol to try and remove any deposits that may be in there.
-Replaced fuel filter, and air cleaner
-Replaced the TPS (it was bad, giving me an error code)
-Replaced spark plugs, spark plug wires, and removed all corrosion from the points on the dizzy cap (yes, I should replace the cap and rotor, but I wanted to first try cleaning it to see if it made a difference)
-Replaced O2 sensor
I'm kinda stumped, it's like the ECM is dumping way too much fuel in there for some odd reason, then not correcting for it even though the O2 sensor is showing some crazy readings (before going into closed loop the sensor is pegged at 1 volt, then after going closed loop it will occasionally drop to 0.2 volts or so (only for a split second) then pop right back up to 0.8-0.9v for 5-6 seconds).
I've read that it should be alternating between rich/lean in closed loop much more frequently, though I have no idea why it's not.
Any ideas?
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Well, I loaded your data log into excel.
Couple of comments and questions
MAP appears to be functional
IAC is commanded
CTS is functional (reads back in degrees F)
TPS is a bit strange - do you have set up in % - I am used to see mV
Rich Lean counter - is stuck!
It appears everything is fine until you enter CL. At that time ECM sees that O2 is rich - 650 mV and attempts to remove fuel. BLM drops to lowest possible value 108 with occasional reset to 128. There are no cross counts - i.e. since O2 never drops below 450 mV. In your post you've mentioned that you have a new NBO I would assume that its OK (BTW, which model is it AFS-21?), unless it was silicon poisoned. It happens occasionally. I do not think its true since you can smell that its running very rich! The other possibility is a stuck or leaky injector. Take a look at injector spray. It should be nice and uniform, there should be no drips or stream of fuel - it should be a misty spray. Do you have 305 or 350 injectors???
yeah the CTS is in Fahrenheit and TPS is in % (It seems I need to adjust it, idle is showing 5.5-6%, should be zero. I had to turn up the idle stop to raise the idle speed, it would run very rough under 1000rpm due to being so rich)
Yeah I replaced the O2 sensor not too long ago, it appears to be working, the engine is definitely running rich, makes a small amount of smoke and smells pretty rank
I could hear the engine speed up as the ecm lowered the BLM's, but I guess it would fail to lean it enough to get a cross count, go back to 128, and the engine would slow down again.
So either the ECM is bad, or it's a fuel system problem (too high fuel pressure, bad injectors), right? AFAIK the injectors are the correct ones, do you have a part # I can compare with?
what is the normal duty cycle for the injectors at idle? (to rule out an ecm problem)
Check injectors and fuel pressure first. FP should be between 11 to 14 PSI. TBI 305 should be equipped with Green-White color coded - 5235279 *RPD injectors. Larger 5.7 liter injectors will not result in better performance on a stock 5.0 L engine. At idle, injector duty cycle is relatively low. Also, check injector coil resistance - TBI injector coil should be between 1 to 2 Ohms, typically 1.2 to 1.3 Ohms when measured with a quality DVM.
ECM is most likely OK.
TPS could be off for several reasons. Check if the minimum idle screw has been tempered with(driver side of the TB, toward front - TORX-25). I do not recall if '91 has an adjustable TPS ( i.e. one of the mounting bosses has a slot). Minimum idle screw may have been tempered to compensate for rich mixture.
If you can wait a couple of days, don't buy new injectors, just send them to http://www.witchhunter.com/ to have them cleaned and flow tested for $17. each plus $10. shipping. The flow measurements will also allow you to verify that they haven't been swapped for a bigger injector, although you'll need to correct their numbers to lbs/hr and 12 psi.
I'm having the exact same problem, and have replaced all of the same things that the OP has, plus some(coolant temp sensor,EGR valve and solenoid,etc.), and I believe that I am down to only two possible problems. Those being either a bad ECU or PROM, or that someone replaced the injectors at some point with ones for a 350. My question is how do you tell the difference between 305 and 350 injectors. I see that color coding was mentioned above, and I have 4 injectors(two that were in the car when I got it, and two from a truck TBI unit I got from the junkyard). All of them are marked with an orange stripe on top. I have tried both sets, and the spray pattern appears to be good with both of them.
Also, I don't know if the OP's car is doing this also, but when the car warms up, it will idle fine for a minute or two, then will surge up and down a couple of times, then go back to idling normally(maybe the computer is trying to dump a little extra air in there at this point?). While the idle is jumping up and down, you can hear a sort of buzzing/clicking sound coming from the TBI unit.
I would also appreciate some sort of input on this, as I have taken it to the shop twice for a diagnostic check (at $60 a pop), only to go back home and replace what they told me they thought it was, and have it not be the problem.
305 (5.0L) injectors were marked with green-white paint marks. A common 305 injector part number GM 5235279 *RPD. Naturally, there are many other service part numbers. Post what you have, as I have a small collection of 305 and 350 injectors.
350 (5.7L) injectors were marked orange - black marking. A common 350 injector part number is GM 5235206 *RPD. Sounds like you have all 350 injectors.
The buzz that you hear is IAC trying to control the amount of idle air to keep engine from stalling. You may want to re-set IAC - its a simple procedure. Check technical articles section for detailed info.
//RF
Last edited by RFmaster; 02-17-2008 at 01:54 AM.
Reason: More info
All right I got the new injectors, it runs a LOT better, still a little off though
acting on a hunch I replaced the O2 sensor again, it had fouled up from the engine running so rich
it's a lot better, but still runs slightly rich in OL, and in CL the BLM's are mostly in the 112-118 range.
It idles really smooth now! 650rpm in gear, 800-850 in neutral, no shakes or vibrations, but it does occasionally make a "pop" out of the exhaust. I think I may just need to adjust the timing or something.
Oh well, I guess I can't get it perfect, but it's certainly not bad for a 98,000 mile engine that's been sitting for 3-4 years.
Looks like you got this problem licked! You may want to reset ECM by disconnecting negative battery terminal. Also, check for other usual suspects such as vacuum leaks, distributor parts and dried up spark plug wires. Check and clean plugs. Timing is should be set with timing set connector open. Check your under hood label, but your initial timing should be around 6 degrees. Once timing is set re-connect timing set connector, shut engine off and disconnect negative battery terminal to clear code 41.
ok same story here except mine was running rich because of an exhaust leak @ the manifold " bolts werent tight enough" ,ok so before i tightened the bolts my car would run super rich " i mean white smoke that would fill up the street and still linger in theair after i shut it off" , so setting my spark timing to a little BTDC and tightening my eshaust manifold bolts made the smoke go away but there still was that rich odor so i set my timing to 0* TDC and it got worse , i was getting codes 33 42 and 15 , got rid of 33 and 15 but cant get rid of 42 now my question is , could my brand new bosch o2 sensor have gone bad after running it in super rich conditions ? i still have the old sensor , i'll try putting the old sensor back on but if that dosent work what else could it be ? btw the car runs rich from startup to when its warm . it also makes my car surge " the dome light and dash lights dim "
ok same story here except mine was running rich because of an exhaust leak @ the manifold " bolts werent tight enough" ,ok so before i tightened the bolts my car would run super rich " i mean white smoke that would fill up the street and still linger in theair after i shut it off" , so setting my spark timing to a little BTDC and tightening my eshaust manifold bolts made the smoke go away but there still was that rich odor so i set my timing to 0* TDC and it got worse , i was getting codes 33 42 and 15 , got rid of 33 and 15 but cant get rid of 42 now my question is , could my brand new bosch o2 sensor have gone bad after running it in super rich conditions ? i still have the old sensor , i'll try putting the old sensor back on but if that dosent work what else could it be ? btw the car runs rich from startup to when its warm . it also makes my car surge " the dome light and dash lights dim "
Start a new thread - your problem is probably different.
