rough after warm up
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
rough after warm up
I have a 91 with rebuilt ecm and hypertech (thermo chip) from the previous owner.
All was well until recently at a stop light it started idling rough. If you gave it some gas and let up it would want to die. It would run down the road but didnt fell smooth and would die when you let off to turn onto another street. Now, it starts okay but as soon as it warms up it wants to go into the "loping" mode.
Checked codes, nada. Checked fuel pressure, steady at the high side of 38 to 39.
Can a leaking intake cause this? I have a little anti-freeze sitting on the aft left side of the intake. Can't see anything else that might leak antifreeze. This thing has been one thing after another. only 113k on the clock.
thanks
All was well until recently at a stop light it started idling rough. If you gave it some gas and let up it would want to die. It would run down the road but didnt fell smooth and would die when you let off to turn onto another street. Now, it starts okay but as soon as it warms up it wants to go into the "loping" mode.
Checked codes, nada. Checked fuel pressure, steady at the high side of 38 to 39.
Can a leaking intake cause this? I have a little anti-freeze sitting on the aft left side of the intake. Can't see anything else that might leak antifreeze. This thing has been one thing after another. only 113k on the clock.
thanks
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
Still not running right
Well did a few things yesterday. Seems the EGR solenoid didnt check out per the haynes manual so I went looking fora another. Seems they dont exist at GM anymore. The AC Delco store found a "similar" solenoid, just a different bracket (the solenoid is obsolete even at PepBoys). Only problem is the sleeves on the electrical plug were different. Knife fixed that. Started the car and it ran rougher than before.
But wait, it started throwing a code 33 (MAP). So I changed the MAP sensor. Started running smoother but still same goofy intermittent lope in it and not smooth. Since there is some antifreeze sitting where the intake bolts up to the head (left rear) and its not coming from the thermostat housing, I'm guessing a leak there. No obvious antifreeze in the oil but maybe its just burning off. New gasket set is on order, not like those are handy as they have to order them (I didn't think TPI was THAT rare). So I'll rip that apart by next week. Hope that takes care of it as the vette makes a lousy coffee table but a good boat anchor. Maybe this is why the mustang is so popular.
But wait, it started throwing a code 33 (MAP). So I changed the MAP sensor. Started running smoother but still same goofy intermittent lope in it and not smooth. Since there is some antifreeze sitting where the intake bolts up to the head (left rear) and its not coming from the thermostat housing, I'm guessing a leak there. No obvious antifreeze in the oil but maybe its just burning off. New gasket set is on order, not like those are handy as they have to order them (I didn't think TPI was THAT rare). So I'll rip that apart by next week. Hope that takes care of it as the vette makes a lousy coffee table but a good boat anchor. Maybe this is why the mustang is so popular.
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
well, pulled intake apart to change intake gaskets since i had a coolant leak. changed a couple other things like the egr and a a couple of temp sensors. Ran okay to start with but it still goes into a loping idle almost like its cutting out then run, then cut out. I'm wondering if its bad gas as it started out of the blue while driving home from coffee. I'm pretty much at a loss at this point. It makes a lousy flower box.
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
I really hate throwing parts at something but I'm at that point. I replaced the electronics (module and capacitor) in the distributor while it was apart. Checked the coil and pickup and they check out according to the manual.
Replaced the inline fuel filter while I was at it. Fuel pressure reads about 39 while its running (high side but within what the manual said).
I've checked the vacum and at idle it pulls about 15 to 16 inches. It runs okay (doesnt quite sound right though) when its cold but once it warms up it will go into a loping cylce. If it doesnt die it goes away for a bit and then cycles again.
About the only thing I haven't tried is the IAC. I'm certainly open to sugestions.
frustrated
Replaced the inline fuel filter while I was at it. Fuel pressure reads about 39 while its running (high side but within what the manual said).
I've checked the vacum and at idle it pulls about 15 to 16 inches. It runs okay (doesnt quite sound right though) when its cold but once it warms up it will go into a loping cylce. If it doesnt die it goes away for a bit and then cycles again.
About the only thing I haven't tried is the IAC. I'm certainly open to sugestions.
frustrated
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
I suppose I could try the O2 sensor but I replaced that maybe a couple of years ago when I first got the car.
It's not throwing any codes so apparently the computer is happy with the sensors.
I've tried plugging or disconnection the vacum sources but it doesnt seem to make a difference (yes if left unplugged it will make it run like crap but I put a plug in to see if the vacum changes.)
By the way, thanks for the response.
It's not throwing any codes so apparently the computer is happy with the sensors.
I've tried plugging or disconnection the vacum sources but it doesnt seem to make a difference (yes if left unplugged it will make it run like crap but I put a plug in to see if the vacum changes.)
By the way, thanks for the response.
Burning Brakes
Joined: Aug 2006
Posts: 1,061
Likes: 99
From: Seattle WA
Symptoms sound like your injectors could be going bad. Did you test them with an ohm meter? If not, just unplug each injector connector and test the resistance across the two terminals. They should each read 15-16 ohms.
When you have an injector or two failing, the car will often run ok in open loop but idle like crap in closed loop.
When you have an injector or two failing, the car will often run ok in open loop but idle like crap in closed loop.
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
I'll check them out. Its really weird cuase it will idle okay for a bit then get into this lope surge thing, almost die then settle down again. I'll take a look at the injectors.
How can I tell if its closed or open loop?
thanks
How can I tell if its closed or open loop?
thanks
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Burning Brakes
Joined: Aug 2006
Posts: 1,061
Likes: 99
From: Seattle WA
The main parameters for closed loop are coolant temp around 160 deg and O2 sensor voltage indicating the sensor's warm enough to read.
You can't tell for sure exactly when it's open loop or closed without datalogging.
The reason you'll see a big difference in idle quality and general smoothness closed v. open loop with a failing injector is that the o2 is only being read as the average of one cylinder bank, yet adjustments are made globally to all cylinders/injectors. When an injector goes bad due to the coil shorting, it will fire lean and throw the whole system out of whack. If you have a couple failing injectors, it will load up the ECU so much that the whole bank won't fire intermittently. The '88-'91 injectors are notorious for this behavior.
You can't tell for sure exactly when it's open loop or closed without datalogging.
The reason you'll see a big difference in idle quality and general smoothness closed v. open loop with a failing injector is that the o2 is only being read as the average of one cylinder bank, yet adjustments are made globally to all cylinders/injectors. When an injector goes bad due to the coil shorting, it will fire lean and throw the whole system out of whack. If you have a couple failing injectors, it will load up the ECU so much that the whole bank won't fire intermittently. The '88-'91 injectors are notorious for this behavior.
Burning Brakes
Joined: Aug 2006
Posts: 1,061
Likes: 99
From: Seattle WA
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
Wow, what a diff one injector makes! Seems to be running great now. Took it around the block. Going to try it for a quick run to confirm.
thanks much for the info. Been wrestling with this for a while. None of my manuals had the ohm readings for the injectors. Guess I need the regular shop books.
thanks again
thanks much for the info. Been wrestling with this for a while. None of my manuals had the ohm readings for the injectors. Guess I need the regular shop books.
thanks again
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
Car runs great, job well done on diagnosing the injector! I'll remember that check.
Well, now there is a new problem. The cooling fans dont want to work. The fans work when you jump E and A so they have a good ground and power. Grounding F doesn't make em work so supposedly the computer is okay.
The last check was D, which has no power or just a trickle (not even 1 volt). I love this repair " If there is no voltage check the ignition fuses and wiring and replace as necessary." So far I haven't found any fuses marked Ignition and exactly what wires would they be talking about? Love these manuals.
Once again, thanks for the help.
Well, now there is a new problem. The cooling fans dont want to work. The fans work when you jump E and A so they have a good ground and power. Grounding F doesn't make em work so supposedly the computer is okay.
The last check was D, which has no power or just a trickle (not even 1 volt). I love this repair " If there is no voltage check the ignition fuses and wiring and replace as necessary." So far I haven't found any fuses marked Ignition and exactly what wires would they be talking about? Love these manuals.
Once again, thanks for the help.
Thread Starter
Heel & Toe
Joined: Oct 2007
Posts: 18
Likes: 0
Initially I couldn't find a fuse for the fans. They had power going to them when you checked the terminals. Since I couldn't find anything else and the fans in fact would run, I tried again to find a fuse. Nothing in the manuals but I did find the fuse section in the corvette owners manual. Along with twenty other things, the 10amp fuse marked for Gauges also has the fan relays. And yes it was fried. Replaced the fuse and "viola".
Not sure what caused it so I'll have to keep an eye on it. I did notice the red "hot" (E) wire on one of the fans looked a little cooked. Not sure what would have caused that unless the fan was running too much. I should double check to make sure both fans are working. Could be a combination of one relay making the other fan over work?
No, really, I like this car.....
Not sure what caused it so I'll have to keep an eye on it. I did notice the red "hot" (E) wire on one of the fans looked a little cooked. Not sure what would have caused that unless the fan was running too much. I should double check to make sure both fans are working. Could be a combination of one relay making the other fan over work?
No, really, I like this car.....
