BigDaddy5

The '85 has been running like a champ for a while now, so I knew I was against borrowed time and now it's time to pay the piper. I haven't really messed with the engine in a while, and the last thing I did was remove the throttle body, clean it out, and reset the idle.
This was last summer, and she ran fine for the last year. Without any noticeable prior indication of an issue, when I went to start her up, the idle jumped to about 2K and immediately fell before stalling out. I also was left with a nice eye-burning aroma in the garage after, so I assumed it was running lean.

I tested fuel pressure, was reading 45 consistently at the rails, so I took off the injectors and tested them. They all are aftermarket, and tested 16.6-16.7 ohms. I also cleaned them, and they all opened when 12v was applied.

I also replaced all of the spark plugs, although they too were aftermarket and the car only has 70K miles on it, I figured I'd knock that out while I was at it.

Once I got it all back together, no change. I played with the throttle a little to coach it to life, and the idle was able to hold but it was rough and sounded a little like it was possibly backfiring as well. Also, when I touched the throttle, there was a significant hesitation before finally jumping up in RPM.

I also checked the usual suspected, disconnecting the MAF sensor, and ensuring TPS was at .53v, but no change.

If anybody has any other suggestions, I'd love to hear them. Thanks!

ex-x-fire

Ohm the coolant temp sensor, when the engine is cold, it should read the same ambient temp. Then do it as it warms up.

BigDaddy5

Thank you for the suggestion. I recently, about two years ago, replaced the water pump. When I did that, I also replaced the coolant temperature sensor.

billschroeder5842

Yeah, this is my initial reaction too.

Those little gizmos really drive a lot of functions on our cars. My neighbor has a '96 GS and it completely "overheated" on him and the engine shut off. Funny thing was that we shot the engine with a thermo gun and it read normal.

Swapped out the Collant sensor and now it is good to go.

gerardvg

Hi

You mentioned you removed the injectors to test them, did you remove the connectors correctly or tugged them free with the wires?

I mention this because i had a problem with my injector connectors, there is a thin metal strip that can be damaged if you pull the injectors by the wires. I was about to sell the car because it ran rough and was missing badly, one night i woke up and thought of an easy way to trace the problem to one cylinder.
Started the car at like 2am, ran it for 20 or 30 seconds and felt the exhaust at the headers an inch from the heads.
Hot , hot ,hot , huh WTF one was cool, swapped the injector plug from the injector next to it and transferred the problem!! YES i yelled in excitement.

Months before i had actually tested all injector connector plugs, popped them of the injector turned them over while checking the 12v pulses with a multi meter (obviously turning the plug over made the circuit). I had thought all was ok , Obviously a broken strip of metal in the connector wont pass the power to drive the injector.
I had checked the spark plug leads were ok new spark plugs same. Compression good even changed the ecm, ignition module and injectors you name it.

Got new injector connector plugs and started her, she ran perfectly power restored.

I had experts look at my car and they were stumped, i managed to fix it myself.

Another thing to check is the EGR valve moves freely, probably easiest to check with a flash light and connecting the EGR vacuum hose to the manifold vacuum and check it opens and closes.

Disconnecting the ecm connector near battery or battery and reconnecting it solves some issues, the ecm can get itself in a knot trying to compensate for a error. Most of my problems were resolved with a simple ecm reset clearing codes.

Retarded ignition can also cause backfiring or popping in intake, check the knock sensor is connected and wire to knock sensor is not shorted to the engine.

Even a MAF problem can result in backfire from running too lean or when accelerating.

Good luck

BigDaddy5

Thank you for those suggestions. I'm not leaning towards a bad injector plug, because it was having problems before I clean them. After I clean the injectors, there was no change. So I didn't make the problem any better, or any worse.

The EGR was next on my list. Thanks for confirming that suspicion. I will check that. I'm also going to double check all of the distributor wires for resistance, and make sure none of them went bad.

I will clear the ECM as well. At this point, I'm just trying to track down what could've caused such a sudden onset of problems.

oh, and the MAF is also relatively new. Less than five years old.

BigDaddy5

So quick update, cylinder 2's spark plug wire had extremely high resistance, so Ive ordered a new set all together. When I unplugged #2, the symptoms were still the same, so I'm hoping that's the cause. I'll update when they get here.

HickmanC4

On the 85s, is the distributor under the water pump as it is in my 94? Just finished replacing the Optispark distributor and the water pump this past weekend...no more rough idle, sputtering on take off, and no hesitation...

Does your throttle body have coolant flow to it that may have spilled out during cleaning?

BigDaddy5

Nah, the water pump is in the worst possible spot while the distributor is in the highest possible spot. Water pump requires nearly every accessory to be taken off the car, while the distributor is between the firewall and plenum.

Man, I just googled the LT1 distributor location. Jeez...

Thanks though!

HickmanC4

I just finished replacing both...not the most difficult, but, the most time consuming...good luck!!

BigDaddy5

Another quick update. I've been traveling but I'm working on this while I'm home.

I replaced the EGR, even though it wasn't stuck (I'm hoping it's just gummed up and reacting slow, causing lean), but I broke the EGR sensor so I've got that ordered and on the way.

Hopefully thats what it is!

BigDaddy5

So I replaced the EGR valve and EGR sensor, and it cleaned up a little, no more stalling however I'm still getting the eye burning lean smell, hesitation on throttle, and occasional plenum "popping" around 900-1k rpm.

Anything else I can track down that would cause a sudden onset like this?

BigDaddy5

Another update. Replaced the distributor cap and rotor (distributor was replaced about 12k miles ago, but the rotor and cap weren't), all 8 wires, and EGR valve/sensor. I got the car to settle down at .54 volts without stalling, however it still hesitates when accelerating and it still backfires in the intake. The lean eye-burning sensation is reduced but still there after a while.

So far I've replaced O2 sensor, coolant temp sensor and checked resistance, EGR valve/sensor, distributor cap, rotor, wires, tested the MAF sensor, reset the IAC and confirmed TPS at .54v

I'm thinking next steps are to check the AIR check valves and then try a compress test.

If I'm missing anything or anybody else has ideas, I'd love to hear them! Thanks!

ex-x-fire

Did you test the fuel pressure & bleed down rate?

BigDaddy5

Sure did. Fuel pressure is stable around 40psi, each injector seems to be firing correctly.

Thanks for the suggestion though!

71VETTEWI

Did you check the IAC?

BigDaddy5

damn sorry I missed this. Yes, I did. In fact, I just replaced it last weekend just in case.

so, I was able to pull codes. I thought I didn't have any, but it turns out my check engine light bulb was burned out. So to recap:
still having a rough idle and stalling.
New: codes 23/33

so far I have replace: TPS, IAC, coolant temperature sensor, all vacuum lines, MAF burn off relay, plenum gaskets, EGR valve and sensor, spark plugs and wires, distributor cap, cleaned and tested injectors.

update: cleared the codes, they didn't return. I feel like I'm starting to hear a vacuum leak somewhere but spraying with carb cleaner doesn't change the idle.

Im leaning towards head gaskets now unless someone has any other (and ideally less labor intensive) ideas!

BigDaddy5

So I removed the throttle body and taped up the plenum opening. I blew some smoke into the open vacuum line now (throttle body) and I think I got some coming out of the passenger side plenum/runners. I removed the runner and saw that the new gasket I had only had about 1mm of surface area touching on the bottom part of the plenum (the small opening for the small line next to the bottom bolt). I'm hoping this is the issue. I've ordered new gaskets from ecklers anf I hope that'll fix my issue. There wasn't any obvious signs that the gasket wasn't working on it, however there was some black above that hole. I'm hoping the small surface coverage was causing a leak, despite any lack of obvious signs. I'll keep you posted!

confab

I parked mine and it was FINE.. Everything was great.

I let it sit too long and the battery went low. Charged it and it behaved about as you describe. ECM was bad. (2nd one)

I put a scan tool on it and it was reading weirdness, then it wouldn't connect..

Replaced it and it runs just like it did before.

BigDaddy5

I'll keep that in mind.

I'm definitely leaning toward vacuum right now, though. I could hear the air escaping when I disconnected the throttle body and ran air into the lines with the plenum sealed.