navy02ws6

91 RS, 305 TBI/auto. Car starts, but runs extremely rough, and has no power whatsoever (pushing the gas pedal in drive does doesn't even move the car). Have checked all plug wire connections, checked for vacuum leaks, tried cleaning and resetting the IAC/idle speed, replaced ignition coil, coolant temp sensor, ignition control module, MAP sensor. Following items were replaced within the last 5 years: cap, rotor, plugs, wires, IAC, TPS, EGR valve, EGR solenoid, fuel pump relay. Check engine light is NOT on, no codes other than 12.

I had this same problem about 4 months ago, only difference is that it only occurred after a cold start, and would go away after about 5 minutes. Car now runs very rough all the time. When it first did this 4 months ago, I replaced the fuel filter, and got a steady 13 psi with a fuel pressure gauge attached. Base timing was set at 2 degrees, idle speed was set at 625, and throttle body was rebuilt at the same time. Car is my daily driver, and has ran fine since then, no problems until I tried to leave work 2 days ago. Car does not have a catalytic converter.

No idea what's going on here. Any help at all would be greatly appreciated.

Schurkey

What is the fuel pressure NOW?

Perform a cylinder-balance test to discover dead/weak cylinders.

Is the computer controlling the idle speed? I find that when folks dick with the base idle screw, it rarely ends well.

Was the ignition timing set with the EST disconnected? Does the timing advance work?

Connect a scan tool, look at the data stream--especially the coolant temperature, MAP sensor, fuel trims, knock sensor activity.

navy02ws6

Just checked fuel pressure again with both just the key on, and also with the car running (rough), still 13 psi both times.

Haven't tried adjusting the idle screw again since the car started running like this. Thank the sticky on this site for telling me to adjust the idle screw.

Timing was set with brown EST wire disconnected. Timing advance was working perfectly fine before it started running like this.

I don't have access to any OBD1 scan tools, so that will be a last resort as I don't have money for one right now, and they're far more expensive that any part that could be replaced (other than an entire engine assembly).

tom3

Going way out on a limb, but what you're describing sure sounds to me like water in the gas. Have to unhook a fuel line. pump a half gallon of gas into a clear jar/bottle and look for water in the bottom. Where do you buy gas?

navy02ws6

Just finished hooking the fuel lines back upI've always bought gas at Quik Trip. Doesn't it have to be somewhat cold out to get water in the fuel? Haven't had a day below 60 degrees here in weeks, and car ran fine for nearly a week after filling up last time.

I'm now getting a check engine light and code 33 (MAP sensor high voltage), but *only* when I give it gas while it's running like this. Check engine light comes on for a second while giving it gas, then goes away immediately as soon as I let off, but the code still stays in history (shows up when I pull codes with a paper clip). With the car running, pin B on the sensor (MAP voltage) shows about 3.5V, then climbs until the car stalls. I've read in other threads ( https://www.thirdgen.org/forums/tbi/...ap-sensor.html ) that it's only supposed to be 1.2-2.0V. Maybe the MAP sensor is bad after all?

Komet

Swap it out and see what happens. Wrong MAP voltage will certainly cause issues.

Schurkey

Excellent.

As long as the screw is adjusted properly, great.

Doesn't matter if it WAS working perfectly. IS is working NOW?

Put a vacuum gauge onto manifold vacuum--perhaps by putting a "Tee" into the MAP vacuum hose. Verify that the vacuum "is" where the MAP says it is.

Remember, an engine that runs poorly will have poor vacuum. It can be a result, not a cause.

navy02ws6

Tried changing the MAP sensor out with a known good one, no difference. I think it's just trying to compensate for something else, hence the high voltage/code 33.

Going to hook up a smoke machine to it and see if I've got any vacuum leaks -- it sure sounds like it does, all of a sudden.

Schurkey

A person can change the sensor every day and twice on weekends...if the wire harness is defective, replacing the sensor won't help.

Thus the suggestion to connect a scan tool--you'd know what the computer is seeing for sensor outputs.

Sensors respond, they don't "compensate".

Not a bad idea.

stew'86MCSS396

Just throwing this out for a different thought process... The link^^^posted was a good read on checking the MAP ref voltage, signal, and ground...none of which you have reported/mentioned but we can chalk that up as bad wiring providing misinformation or is it really telling you the truth. Truth of the matter is in $61 auto bin, idle rpm is targeted at 525 rpm. Somewhere in this thread, you adjusted it to 625 rpm. I believe with the ECM trying to target 525 rpm, the IAC is going to slam shut to 0 where it can't adjust anymore and the remaining air going through the throttle blades may be picked up by the MAP sensor as a vacuum leak but I wouldn't think it would run like crap just a higher than normal idle and maybe some richness from the higher kPas being reported.

navy02ws6

Still trying to get the smoke test done -- in the meantime, idle is set back at 525 rpm, and timing is set at 0 degrees with EST wire disconnected. Timing with EST wire connected is at 16 degrees advanced. Car still runs the same. Disconnected the battery for a few minutes after setting the timing, car is now showing no codes.

navy02ws6

Likely going to buy a Moates cable if I can't figure this out after checking a couple more things, including going through the "runs like a$$" chart in the factory service manual -- had no idea they were that cheap and/or worked, was thinking I'd have to spend $300+ on a dedicated OBD1 scan tool.

tom3

Did you try unhooking ALL the vacuum lines, including PCV and brake booster?

tom3

Also with the TBI you can get a good light and check the injector sprays at idle. Not unusual to see a dribbling injector rather than the really fine mist pattern.

navy02ws6

Still waiting for the smoke machine to get here -- rather certain it's a vacuum leak at this point, I took a bunch of vacuum lines off then put them back on (mostly MAP and EGR solenoid), car ran great for about 20 minutes, now back to running rough again.

I really wish someone would make a pre-bent hard vacuum line kit for these cars. All of my hard vacuum lines are broken and patched with bits of straight hard vacuum line and rubber lines connecting them together. Wish there was a more reliable option, but a lot of the fittings on the ends are permanently attached to the old hard lines.

navy02ws6

Turns out that's the main problem -- passenger's side injector was slowly dripping, and now will not fire at all. Also had a leak at the TBI base gasket, and PCV hose going to the TBI was torn at the 90 degree bend, also not helping vacuum. Still waiting on a replacement injector to get here. Car ran okay Friday (drove it home) when the injector was dripping, but now will not run at all since the injector completely quit.

Schurkey

How do you know it's the injector, and not the wire harness powering it; or the ECM that grounds the circuit?

Did you connect a Noid light to the harness and see if it blinks?

navy02ws6

I swapped the harnesses between the two injectors; no change from either injector after doing so.

navy02ws6

Replaced the bad injector, replaced the TBI base gasket again, replaced the PCV hose. Went ahead and replaced the PCV breather and air filter again too. Car runs good now! Thanks for everyone's help with this.