89 L-98

Hello all, posted a thread earlier about this but was wondering if someone could clear up how the IAC solenoid works in open compared to closed loop. AND is it engine temperature that puts the whole thing in closed loop?

The car runs fairly well at idle when then the warmer it gets, the worse the surging at idle. It runs like jet when accelerating. The idle just gets terrible and hunts from 500 to 1000 back and forth. Car ran great at idle before replacing injectors.

Unplugging the TPS for some reason absolutely stops the hunting, but it idles too fast. Why would unhooking the TPS stop the hunting?

I am going to check TPS tomorrow, set the min idle and also reset the IAC per some other threads. I hope this helps, but just wanted the knowledge so I can continue to troubleshoot this .

Thanks
Gary

 

sounds like you may have a vacuum leak if it has a high idle with the TPS disconnected and the min idle screw backed off. You can spray some easy start around and see if it surges.Perhaps you disturbed something changing the injectors.

 

The ECM uses the IAC to open and close the air port in the throttle body according to temp vs rpm tables. Colder temp equal higher rpm. The TPS sends voltage signals to the ECM according to the position of the throttle blades. Closed loop is when the exhaust temp reaches ~600* and the O2 sensor becomes active.

I agree, sounds like a vacuum leak.

 

I am checking out all advise, thanks.. Will shoot some propane at it tonite again to try to find a leak. I agree this is a definite possibility from having everything apart.

If it is a vaccum leak why would disconnecting the TPS make it run even? The leak would still be there..Just trying to learn.

Gary

 

From what I am thinking, when the TPS is disconnected the ECM commands the IAC to open fully...thus the high idle. This is why there is no surging as the ECM is trying to move the IAC back and forth to control the idle.

 

I had another think about this and it would seem that disconnecting the TPS would cut the voltage to the ECM and give you an even leaner mixture.If it's a vac. leak it should be lean already.Keep us posted.

 

Hello guys, thanks for your help so far. Progress report....

Well the idle settled down to around 600. Nothing in particular I can say fixed that part of it. I reset the IAC valve, checked TPS, it was ok and then cleared codes that were set while doing this..The computer must have finally learned the sensors after driving 30 or so miles.

HOWEVER, what I have left is an erratic miss the warmer the engine gets. And I think this is why it took so long to get the idle calmed down. When cold, I do not feel it. When the water temp hits about 160 or so,just like clockwork, the miss gets more pronounced. It is like a quick stumble. I don't know, feels like ignition related, because it comes and leaves so quickly. I took it for about a 50 mile trip yesterday and can feel it when cruise control is on. Bucked fairly hard 2 or 3 times.

Car has new wires, plugs, cap, rotor, thermostat, fpr and Bosch 22 lb injectors. Everything is stock on the engine otherwise.

Wires ohm out good. Replaced plugs again, no change. Fuel pressure while running and when the miss happens is rock steady.

Did not have this miss before starting all this winter maintenance. I hope I don't have an injector problem, but I will take them back out, as a LAST resort. Getting to them is a B#*'CH as you know. They ohm out perfect, cold and hot and were flow checked extensively before installing.

I am checking to see if a guy that works on my other vehicles has a diagnostic machine that can be hooked up to this vintange to see if I can determine if it is ignition or fuel/air.

Thats my next step, really getting a lot of time wrapped up in this, want to move on to other maintenance issues.

Gary / Louisville

 

Possibly ignition module and don't believe the posts that say they either work or don't work.They can become intermittent.The warmer it gets issue leads me to believe it could be the cause.It's a $30 item and may fix the problem.Also I'm not aware of any codes it would throw if it is the culprit.

 

My 89 sounds like its doing the exact same thing as yours. I have checked and replaced everything you have and after having it looked at by a shop I have been told its probably in the distributor. What (Staugur) says above makes sense , it could be the ignition module or some other part in the distributor or maybe the distributor itself. WW

 

I am going to pop off the distributor cap next I guess, look for carbon tracks, etc. I don't have a Helms book, but the (normally almost useless) Haynes book does give some tests including a wiggle test of the pickup coil connector wires to see if there is anything intermittent. I will try this in the next day or so.

Been thinkin about also getting one of those spark check lights that go between the wire and the sparkplug to see if i can see any intermittant pulses right when the misses occur. I wonder if one of those will stand up under the voltages of the HEI? Or perhaps one of those that look like a sparkplug with a ground clamp. Maybe that type would be better to actually check the spark for color, etc.

Anyway, thanks for riding this out with me. Would love to find the magic bullet here and be able to report it. So many threads just die out with no report of the final fix. Now I see why!

 

From what I have read, during open loop the car is running off default perameters directly from the ecm, and most sensors and the,TBS and IAC don't even start working on there own until closed loop. This is why cars sometimes run fine in open loop and badly in closed loop. If something is not working right closed loop is where it will show up.

 

Good luck with that. When I have done it, I could see nothing, including any small cracks. I ended up replacing the cap and rotor after cleaning eveything with electrical cleaner (brake cleaner might work).

You can do the same with a larger screwdriver. The hard part is not getting burned or shocked AND being in the right place when the miss happens.

Have you checked the resistance of each plug wire and the plug-in connections for all the parts you unplugged when you did the injectors? Not a bad idea to clean them, too.

Is the vacuum normal at idle? Reading and understnading vacuum levels can be as valuable as reading spark plugs. Part of the problem with an ECM'ed engine is that small problems can be covered up (adjusted for) . The old tools are still valid.

 

Well..borrowed a Snap On timing light and checked timing tonite. It was right on at 6 degrees. I hooked up the light to each plug wire and tried to observe the spark. Every one was consistant when the miss was happening. I know thats not scientific but it was fun. I also observed that the advance moved on acceleration. Anyway, going to pull the distributor cap this weekend also and check for tracking and do some Coil wire wiggle tests as outlined in my almost useless Haynes manual. As I said, the timing light flashes looked consistant, but hey, who can count that fast?

Still got to get a gauge configured to check vaccum. I am still not ruling that out as a possiblilty. I just don't know why it would cause a problem only hot.

Anyway, I will solve this sooner or later, looks like later. Will keep you posted...

Thanks for all your advise..

 

It looks like I don't live too far from you. (Corydon, IN). I have a 90 vet and a pretty good collection of tools, gauges, & special tools for C4. Let me know if I can help.
Greg

 

Yup. Suckin' air.

If it didn't do it before, you didn't get one of the injectors seated. You should hear it.

But if it was doin' it before the swap, the intake leak is somewhere else, and you might not oughtta' bought the injectors first, till after findin' the leak.


EDIT: Cancel; I see more of your diagnostic posted...