'84 SE 4 spd - At cold start-up, for the first few minutes of driving there's significant hesitation at each gear change, almost like it's not getting enough gas.
With further throttle opening, it lurches forward. After a few minutes, there's no hesitation; presumably due to warm-up.
There are a dozen potential ailments in the FSM to consider; I'm wondering if there's a 'most likely' issue that would disappear after a few minutes warm-up.
I'm wondering if there's a 'most likely' issue that would disappear after a few minutes warm-up.
Do you have the complete "stove" that sends warm air up from the exhaust manifold, and is the temperature controlled valve (mounted in the air filter housing) still functional?
Slightly different application, but relevant info Here.
[This message has been edited by Patrick (edited 11-22-2017).]
Yup, plugged IAC and other things can do this. Not really a shortcut to find the problem. But can look for intermittent vac leaks etc that are cheap/free first steps. See my Cave, Vac Leaks and Emissions
flaky fuel or ignition parts won't help. Even ECM. Anything can be "bad" cold then warmup and run good or other way around depending how part is dying.
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Originally posted by Patrick: Do you have the complete "stove" that sends warm air up from the exhaust manifold, and is the temperature controlled valve (mounted in the air filter housing) still functional?
Slightly different application, but relevant info Here.
Called the Thermac to preheat air to prevent TBI/TB/Carb freezing. All dukes w/ carb or 300 TBI have it. 87 and up deleted it w/ 700 TBI. could be part of problem, more so if has a vac leak, but TBI freezing can happen even w/ engine hot. (v6 used for Fiero have coolant heating TB for same reason.)
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Originally posted by Patrick:Do you have the complete "stove" that sends warm air up from the exhaust manifold, and is the temperature controlled valve (mounted in the air filter housing) still functional?
This issue is on my '84 SE 4 speed with 377,000 km (276,000 km on warranty replacement engine 30 yrs ago...).
I discovered maybe 10 or so years ago that the original 'spout' on the bottom of the air cleaner housing had vanished. I never noticed any changes in performance; just left the tube sticking up from the manifold cover. Four years ago when I put an '87 engine in my '86 I put the '86 air cleaner on the '84 so I could reconnect the heater tube. Never checked to see if it worked; never noticed any change in performance either.
The door can be pushed up by finger pressure and will stay up for a second with my LPVP (lung powered vacuum pump). If I move the control valve reed spring, the LPVP does not keep the door up at all, so I guess both seem functional.
The door doesn't close when the engine is started but I don't know the actuation temperature so it's possible it may be functional.
I wonder how much suction the engine provides to actuate the door?
Originally posted by theogre:But can look for intermittent vac leaks etc that are cheap/free first steps. See my Cave, Vac Leaks and Emissions
I used a plumbing torch to check for vacuum leaks around lines & EGR; there was no change in RPM. There was no change in RPM when I provided gas right in the TB opening either, so maybe that was not a useful indicator.
It idles about 1,000 RPM when warm; so I did not suspect vacuum leaks...
[This message has been edited by David Hambleton (edited 11-27-2017).]
Idle should be closer to 750, my 84 SE idles around 650-700 when it warms up and enters closed loop, with the original 160,000 mile engine and the new replacement engine with now 20,000 miles. Do you have a non-functional cruise control system that may be the source of a vacuum leak? Any change in idle if you bypass/eliminate the cruise control vacuum lines?
Car also ran better after removing and cleaning and rebuilding the throttlebody, if you have not done so already
After reading that post, I suspect more than ever that what I mentioned IS contributing to your "hesitation" issue with a cold engine.
It ran fine for years unconnected, then for the last 4 with the thermac valve unverified; doesn't that indicate the recent problem is likely elsewhere?
Idle should be closer to 750, my 84 SE idles around 650-700 when it warms up and enters closed loop, with the original 160,000 mile engine and the new replacement engine with now 20,000 miles. Do you have a non-functional cruise control system that may be the source of a vacuum leak? Any change in idle if you bypass/eliminate the cruise control vacuum lines?
Car also ran better after removing and cleaning and rebuilding the throttlebody, if you have not done so already
Oddly enough, the original engine idled below 1000 RPM; the replacement only occasionally but most often in rainy weather.
No cruise control.
I did replace the alternator recently as the voltmeter was edging into the warning area over 3,000 RPM. The replacement (from the '86 scrap engine) provides a steady indicated 15 volts. I've tried two different ECMs recently as well; this one is a numbers matching unit. The original died a few years ago; stopped the engine while driving like the key was turned off.
It ran fine for years unconnected, then for the last 4 with the thermac valve unverified; doesn't that indicate the recent problem is likely elsewhere?
Obviously I didn't know the entire history and/or condition of your car... but when an engine develops problems running properly before it warms up, the first thing I'd be checking is the device that was put there by the factory to prevent that very issue.
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Originally posted by David Hambleton:
I could prop the door up & see what happens...
I've never had to check the operation of the heat stove and associated valve on my own '84 Fiero, but I'm sure there's info posted somewhere on PFF describing the correct way to do so.
I've never had to check the operation of the heat stove and associated valve on my own '84 Fiero, but I'm sure there's info posted somewhere on PFF describing the correct way to do so.
Perhaps it's never activated out there in Balmy Coast! I'm certain it should be activiated in cold winter weather here, but I never detected any performance variation when it wasn't connected. All that's needed is a quick look in the opening to see if it closes on start-up.
I connected the thermac vacuum line to the original '84 air cleaner housing that's missing the hot air tube spigot and discovered that at start-up at 13 Celsius, the door raised up to direct the manifold heated air into the air cleaner. That wasn't happening with the '86 thermac valve, so I pried it out of the housing and put in the one from the '84 housing, and re-installed everything. At start-up, the door raised up as it should; a few minutes later the 2000 RPM idle dropped down to 1000 RPM and the door went down so air comes in the side vent, not from the manifold shell. I'll see tomorrow morning when the temperature is 5 Celsius if that affects the performance. Maybe it'll at least improve cold weather efficiency...
No improvement in the hesitation issue between minutes one and three of warm-up was noted. I changed the ECM and PROM and the hesitation disappeared.
I wonder if there were ECM issues due to the erratic performance of the voltage regulator (if the voltmeter was an accurate indicator). After alternator replacement there's a steady indicated 15 volts regardless of rpm (when the engine is on... ).
I am about to go down your route, with extremely similar issues, but on an Iron Duke. It starts and settles down to idle OK.. but will not accelerate. Sometimes it is hard to even start out.. as in push it to 3K rpm and finess it to get the clutch out. You can hear it missing severely. But once on the road moving, runs like a top. I already checked my hoses for vac issues, but had already replaced whatever rubber I could. I even blocked off the brake booster. No dice. Shining a flashlight on the injector spray cone, it does appear to be a partial cone.. not a fully circular cone. My suspicions, or at least what I will check next are.. The fuel pressure. I have replaced that f-ing fuel pump twice in 1.5 years, and what the heck, maybe it is 3 now. And it had similar symptoms of power loss. The ignition system. I have a spare Ign module and set of coils. I wish I had a way to measure spark effectiveness without just replacing things. It did finally throw a code this evening, but I have not had a chance to pull it.
Well, good luck Chris. This issue is on my first Fiero, ordered in Sep 1983, rec'd in May 1984, 2.5L 4 speed, daily driver (excluding wet salty winter conditions) with over 377,000 kilometers (234,000 miles) on it. GM put a new engine in in 1987 at 101,000 kilometers. The fuel tank has never been removed; the original fuel pump and lines are still in service.
Recently, cold weather starts would go like this: Starts fine, idles at 2k, back out of the barn then turn and go down the driveway in 1st without touching the gas pedal. Onto the road, work up through the gears, then decelerate to a stop sign. Leaving that stop sign and the next two, the engine would falter significantly as the gas pedal was pressed, unless I pre-reved it to about 3K RPM. The next stop is about 5 minutes away; normal operation by that point. Idle by then is down to 1K. So, the faltering was occurring only during the second and third minutes of driving.
I fixed the intermittent varying voltage reading issue by replacing the alternator (really to replace the voltage regulator), suggested by the FSM as a potential problem. No change in the issue resulted.
I replaced the Thermac motor so the air intake pre-heater would work, but no change was noticeable. That didn't surprise me since I ran for a few years without a connection at all after the spout fell off the air cleaner housing.
I used a propane plumbing torch to introduce gas around the vacuum areas prone to leaks, but found no leaks. Gas introduced right at the TB opening did not raise the RPMs either so I'm not sure I tested anything...
The hesitation, although significant, was only occurring during a limited time period, otherwise performance was normal. Interesting to contemplate how that could be...
p.s. Chris Eddy; an engineer interested in wires... I'm currently suspecting you're an electrical engineer...
Here's a recent wiring issue I fixed:
After 2 years and 5 tows, I found the root cause of an intermittent no-start condition on my Formula 5 speed. It finally occurred frequently enough that I could actually test for it. The pick-up coil winding wire (0.004" dia) connection to the harness plug wire looked like the worst cold solder joint ever.
