Hey all, new to the third gen scene, also own a 96 T/A which I have no issues with. I just bought an 89 RS, auto, a/c doesnt work, so it's not a factor, but I had to install an IAT sensor in it when I got it, sometimes it will run ok at idle(700-800)rpm, and sometimes not(1500)rpm,the SES light will come on erratically and sometimes when the key on-engine off I cant even pull codes out of it, it will be an erratic flashing or won't even go into diag mode.Sometimes the car runs fine down the road, other times it will start to cut out while im cruising at highway speeds, or it will die when I pull into a parking spot or randomly at a light. Any idea what could possibly be the problem? I had pulled a code for the IAT(23) and the Ignition timing module(42), and have replaced both and inspected wiring, though im confused as to proceed, a gm tech has suggested checking fuel pressure reg as it smells rich..any other ideas? thanks

 

Any ideas at all? Possible ecm problem? I'm clueless as to proceed, as the computer won't talk to me...

 

herbie

 

Lev,

Its sounds like you have a bad IAC valve...Have you tested the valve or replaced it? Also you were only able to pull those 2 codes?

 

I have not yet checked the IAC, though I was beginning to think there could be an issue, Ill do that tomorrow. But I have also noticed that when it finally dies with the key on, the injectors go haywire and spray fuel erratically into the bore, I have disconnected them and turned it over to burn any residual fuel off, and then reconnected, and the next time it fire up, and, if it dies, they don't do it again, until they feel like it later on. Thanks a lot for the response Reg

 

When I had to deal with an IAC problem on my '83 Caddy 4.1L, I didn't have stall issues, just high/erratic idle, is it different on these systems?

 

Alright, now I was able to pull some more codes out, Im getting, 42, 53, and 54. The 53 I had an issue with VATS, but it started after I waited the 15 minutes-weird. Anyway, how about 42 and 54, both make a reference to fuel, either cutoff of relay, and also I already replaced EST earlier in response to 42.....does this ring a bell to anyone?

 

Levman74

Code 42 can also be caused by electromagnetic interference from the spark plug wires getting coupled to the signal wire harness that runs into the Dizzy ignition module, especially if these wires are routed too close to each other.

Code 54 Fuel pump voltage was not present at fuel pump sense line for 2 seconds after the ECM has sent the fuel pump turn on command. This code is generated when key is first moved into run position, FP should prime up for about 2 seconds and shuts off before restarting again during cranking. Check FP relay.

//RF

 

Noted, I'll check wire routing tomorrow, and the FP relay, but since the vehicle will start and run, could this relay cause stuttering? I've also seen that when it dies or even Keyon/engine off, things like the purge solenoid, injectors, and IAC will pulse randomly on and off continuously for a time, even when not in diag mode...Thanks RF

 

Well I think I solve most of the problem of erratic and spastic controllers and solenoids-I found 2 bad/disconnected grounds and that helped immensely, but it still idles high sometimes, and even overheated the engine because it would not slow down, but just before that ignition cycle it also ran for a good 10 minutes and it tried to go into closed loop, SES went off, and idles down, then it started getting squirly and then it died shortly after...

 

Levman

You'll need to describe its behaviour a bit batter than that. The only way to get a better idea is to get ALDL cable with WinALDL running on lappy while it is doing its funny biz. You did not mention which grounds were bad - by the thermostat housing??? Also check the back of the passenger side head - there are might be other grounds that flaky.

Did you ever check your fuel pressure?? A flaky FP may cause idle swings. Fuel pressure should be steady, around 13 PSI for a stock TBI

You can do couple simple functional checks which requires DVM and ability to back-probe connectors. If you are for it here is what you can do, engine at normal operating temperature idling:
MAP - Pin C =5 VDc, Pin B 1 to 2 Vdc at idle, Pin A is ground. (Check hoses for leaks
TPS - Pin A = 5 Vdc, Pin B = Ground, Pin C (Drk Blu) 0.5 to 0.65 Vdc at idle.
CTS Pin A (Yellow Wire) should read 1.5 to 2.0 Volts

If you see voltages jumping or dropping out - check harness for shorts or cuts.

Report your findings.
//RF

 

Hey RF-
I see what you are saying, and I repaired the ground on the backside of pass. and driverside heads, I have not checked F/P, as I lack a tool at the moment, but are you sure that it could change in a split second? I'm familiar with slowly dying conditions involving F/P. I'll check the connectors tomorrow after drill to see where she is at. Thanks

 

Levman

All FI third gens use in tank fuel pump. After years of service they fail, or the rubber hose between FP output to feed through raptures. Today's gas is very nasty to 20 year old fuel hose. The hose may develop a small hole and over time just may burst. FP is still working but fuel never reaches TB. The only way to check this without dropping a tank is to perform a fuel pressure check. You can rent fuel pressure gauge test set from most auto-parts stores.

Basic visual inspection - go through TPS, CTS, IAT, MAP, IAC and re-seat all of these connectors. Take a look at pins, check if harness wire is fully attached to connector pins.

I hope this helps

//RF

 

Alright, I looked over the car, checked all sorts of conections and components,
1-the IAC is absolutely shot, it wont budge, so I adjusted idle manually with it, so thats on the replacement block.
2-the engine runs much smoother w/out EGR connected @ idle, with it on, it runs rough and choppy
3-strong smell of fuel still in exhaust, so will be checking on F/P very soon

 

Levman74

1) IAC is a stepper motor - it uses a four wire interface to traverse air by-pass piston from open to close and in reverse. They either work or do not. If there is a lot of carbon build up they may not function at all.
2) EGR should not be active at idle. Sounds like you have leaky EGR control solenoid or incorrect part number replacement solenoid (from PO). You can verify if EGR valve is ok by connecting a hand vacuum pump to its vacuum port an applying about 10 inch-Hg. The engine idle should stumble and get rough as exhaust gases are now present in intake manifold during idle. Also, this will be a good time to take EGR off and use some carb cleaner and clean the intake manifold EGR passages from build up. Over years carbon build up in EGR passages can wreak havoc.
3) Strong smell of fuel in exhaust may indicate that you are in open loop. Check O2 output with DVM - see if it swinging between 80mV to about 800mV. If you're get steady 320 to 400 mV reading at O2 means that ECM is operating in open loop or in limp mode if you are getting SES light.

Take a look at the fuel spray cone coming from injectors - does it have a nice shape with fuel being deposited at TB walls??

Let me repeat this again - the best way to troubleshoot these TBI systems is with a scanner or with WinALDL on a lappy.

//RF

 

Roger on the EGR-that solenoid is active and providing vacuum @ idle, opening the EGR up. I tried hooking the car up to our Tech 2 scanner at work, but it's too old to even be recognized by it, so I will have to go winaldl then. Yes, the fuel is spraying evenly on the walls, no dripping or sputtering.

 

Levman74

Pull Connector from EGR solenoid - it should be a two pin connector with Pink - black and Gray wires.

Engine off, key off. Disconnect EGR solenoid connector and check coil resistance - it should be above 100 Ohms. If it reads infinity or near 0 Ohms solenoid should be replaced.

Engine off, key in run position. Back-probe the plugged in EGR connector. With DVM measure voltage between pink-black to engine ground. It should read about 12 volts. Perform the same with gray wire - it also should read about 12 volts. When ECM commands EGR to open it pulls gray wire close to ground (0.7 Volts above ground)

Perform a vacuum check of the EGR solenoid to make sure the thing is not stuck open.

Report your findings.
//RF

 

Here's what I have come up with-
EGR Solenoid Resistance-37 Ohms
Pink wire-12V
Grey Wire-0-?V, no voltage present
Vacuum check of NBP EGR Valve-unable to hold vacuum
I also checked EGR ports IAW GM manual test, no carbon deposits nor restriction in intake or exhaust ports.

 

Levman74

So you have Negative back pressure (NBP) EGR, Ok.

37 Ohms is a bit low! I'll double check my spares later tonight. My spares are 6o Ohms.
Procedure involves electrical measurements - perform at your own risk.


With gray wire being at 0.0 Vdc means that EGR control solenoid is always energized. It should not be this way. If you measured gray wire with respect to engine ground while connector is plugged into EGR control solenoid indicates that you have a ground short (gray wire to ground). Under normal conditions you should see 0.7 Volts between gray and ground when EGR control solenoid is energized by ECM. Check harness for shorts.

ECM will be next - disconnect ECM from harness. Measure resistance between Pin A4 and ECM chassis. If you measure 0.0 Ohms ECM has a shorted driver transistor. Sorry...


//RF

 

Well I just obtained an identical parts car, 89, 305, auto...so maybe if I play the parts merry-go-round I can find an easy out-maybe swap ecm's? is there anything special involved with that if it's from an identical car?

 

Alright-since I seem to find a lot of threads on this site without a resolution to their problems, I think I will actually conclude this chapter with what success I have come upon. I have changed out the ECM with another car, and voila! The car runs much smoother, no trouble codes, and less fuel consumption, normal idle, and I can even communicate with the computer. thanks a lot everyone who offered up tips and procedures, would have been totally lost without it! Now it's just the improvement game now...