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| Fredbird | Rough start/Sometimes rough idle | ||
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Senior Guru
 
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Just started last week... (1991 C4)
All of a sudden it's gotten very hard to start, and sometimes when I first start it after it's been sitting for a day it just doesn't want to keep running... start stumbling all over. I'm replacing the Dist cap/rotor because I don't know when it was las replaced and last time I was trying to adjust timing it got the living daylights shocked out of myself... So I think it's cracked. I'm also going to replace the fuel filter because I also don't know the last time that was replaced... and at 109,000mi... it's a good thing to replace. I've also got "On hand" an iginition coil if my current one tests bad, and the Iginition Control Module. Those were two things that were definately referenced in the FSM as possible contributors. I've also noticed that when the car is idle... RPM's seem to fluctuate a bit. It's almost as if it's hunting... Timing is at 6 above TDC, I'm going to also test the pickup coil if I can figure out what the FSM is saying on how to test it... PCV valve is completely clean and free. Plugs and wires are new... (Replaced them a month ago.) I also will try to test the MAP sensor... once again if I could figure out the proper way to do that. Any other ideas? |
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Posted on: 2011/6/16 21:33
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| tjpreul | Re: Rough start/Sometimes rough idle | ||
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Elite Guru
 
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Can you test the fuel pressure? A bad pump will make them hard to start.
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Posted on: 2011/6/16 21:35
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Vegas wasn't built on winners. '92 auto, MSD, Banski, Taylor wires, SS lines, C5 rims, 3.07 gears, white gauges, seats from a '96. Motor: Forged rotating assy, Probe pistons, CC valvetrain, AFR heads, Procharger P1SC |
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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One more thing... Rich exhaust smell seems like it's running rich... and it's having light poping upon deceleration on the highway. Could that be bad 02 sensors?
I know I've got a problem with the egr valve if i'm driving for extened periods of time, the CheckEngineSoon light comes on with 32. However, it's only if i've been driving for a long time and have been giving it heavy throttle and backing off a lot. if i'm just tooling around town... it stays off. |
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Posted on: 2011/6/16 21:37
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Thanks... That's why i'm doing the fuel filter... figure that could be contributing to lack of fuel.
Ahh Columbia Missouri... I miss Missouri... I'm from St. Louis... Hence the name Fredbird... But I'm here in San Antonio now... It's nice... but it' not Missouri. |
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Posted on: 2011/6/16 21:39
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| bogus | Re: Rough start/Sometimes rough idle | ||
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Grand Imperial Pooh-Bah
 
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how does a lack of fuel turn into a rich running car?
How fresh are the injectors? If they are the OEM original pieces of shit, you might be in for some problems. |
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Posted on: 2011/6/17 0:31
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Quote:
Sorry, for the confusion... I was just trying you relay all of what i'm experiencing... I replaced the fuel filter (Cheapest part) and now the car is starting without issue and not stumbling upon start. - Hopefully that's not just a fluke. However, yes at the same time I'm getting that heavy 1980's exhaust smell and the popping upon deceleration (which I assume is unburt fuel combusting in the CAT.) Not sure how old the injectors are. I know at least 1 has been replaced. Because one is black and the rest are gray. (I don't mean to sound ignorant, but I don't know if they are original or not) |
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Posted on: 2011/6/17 1:38
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| tjpreul | Re: Rough start/Sometimes rough idle | ||
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Elite Guru
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If you don't have the proper pressure the injectors won't have a good spray. This can cause unburnt fuel. The injectors are a project on your car, but then you could also get to the EGR to fix it too. FIC is the way to go if you decide to replace the injectors.
Tomorrow is STL vs KC. The fun games to go to are STL vs Cubs. |
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Posted on: 2011/6/17 1:56
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Vegas wasn't built on winners. '92 auto, MSD, Banski, Taylor wires, SS lines, C5 rims, 3.07 gears, white gauges, seats from a '96. Motor: Forged rotating assy, Probe pistons, CC valvetrain, AFR heads, Procharger P1SC |
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| Woodstock | Re: Rough start/Sometimes rough idle | ||
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...and there you go. Grey are the original Multecs and I've never experienced only one to fail, usually the entire bank gets into trouble. One injector is leading the way and the others are soon to follow. Do the simple ohm check, lowest scale on your meter. I bet those values are all over the place. |
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Posted on: 2011/6/17 10:32
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Quote:
Thanks for the explination... Makes sense. I will get to the EGR probably this fall when it starts getting wet outside and I can't drive the car as much. I may check the injectors when I take the pleneum off to work on the EGR. I think the FSM has the values I need to check for when checking those injectors. I will keep the FIC injectors in mind if I decide to replace them any time soon. |
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Posted on: 2011/6/17 11:35
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Quote:
I've done nothing but just peek at them at this point... but one question I have is, the FSM seems to say there's a primary and secondary FI for each cyl., but I only see 8 total. if there's a primary and secondary shouldn't there be 16? or are they hidden back there? |
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Posted on: 2011/6/17 12:00
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| Matatk | Re: Rough start/Sometimes rough idle | ||
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Webmaster
 
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I'm not sure exactly what you're looking at in the manual. The ZR1 has 16 fuel injectors, though.
Rough idle can be caused but multiple issues, one not mentioned is a dirty or malfunctioning IAC. The throttle body may also be carboned up. Two things to look at that are maintenance items. Also, a bad O2 will distort your fuel trim levels. Another maintenance item. I've read non heated O2s should be replaced every 30,000 miles. Matthew |
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Posted on: 2011/6/17 12:27
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| jonszr1 | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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its not a bad idea to replace your o2 sensors. when you do go with the ngks they cost a lot more than the bosch units but are way better builtjmho
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Posted on: 2011/6/17 13:22
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i have a blast playing with my 4 babies 2 zr1s and 2 mustangs 68 coupe with a jon bennit 408 art car fully rollered c4 with a gearvendors over drive .88 mustang built by my kids with a ported lt5 and a bill boudreau blue printed zf 6 spd. with these 4 ... |
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| BillH | Re: Rough start/Sometimes rough idle | ||
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The Stig Moderator
 
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Quote:
They're pretty inexpensive for the 90-92, Brad. Probably because they are single wire (non-heated). $16.69 each NGK-21002 Just put them in my '92. |
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Posted on: 2011/6/17 14:10
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Quote:
Below is what i see in the manual. I will upload a shot from my engine in an hour. Attach file:  Injectors.jpg (470.66 KB) |
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Posted on: 2011/6/17 17:27
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| Matatk | Re: Rough start/Sometimes rough idle | ||
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Webmaster
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Quote:
ZR1 |
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Posted on: 2011/6/17 23:28
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| tjpreul | Re: Rough start/Sometimes rough idle | ||
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Elite Guru
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Quote:
L98 http://www.corvette-guru.com/modules/ ... id=160545#forumpost160545 |
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Posted on: 2011/6/18 2:16
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| Matatk | Re: Rough start/Sometimes rough idle | ||
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Webmaster
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Quote:
Uhhhh...what? He was asking why the fsm shows 16 fuel injectors....because the picture he is looking at is referencing a ZR1. Not because he has one. Matthew |
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Posted on: 2011/6/18 2:52
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| tjpreul | Re: Rough start/Sometimes rough idle | ||
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Elite Guru
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Quote:
I thought this was why he going to upload a picture, so we knew what engine. |
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Posted on: 2011/6/18 3:04
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| Matatk | Re: Rough start/Sometimes rough idle | ||
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Webmaster
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I see. No biggie. As you pointed out, he has an L98
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Posted on: 2011/6/18 3:06
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| flyboy | Re: Rough start/Sometimes rough idle | ||
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Elite Guru
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Vin "J" is ZR-1 stuff.
Vin "8" is L98. I removed most of the vin "J" pages from my FSM reprint and put them in a separate binder to avoid confusion. |
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Posted on: 2011/6/18 3:08
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Sorry for the VERY LONG delay...
I've been working at the church on "Vacation Bible School", had family come in town, took my daughter to the emergency room, and of course Fathers day... But here's the picture I promised. Better late than never... And yes, it's the L98 Engine. The lighting in the picture is not that good, but I think you can make it out. Attach file: Engine.jpg (595.88 KB) |
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Posted on: 2011/6/20 17:11
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Well, at this point I've replaced plugs, wires, inspected Dis cap for cracks, tested the ignition coil, had the ICM tested and it was good. Checked timing, it's at 6 TDC, Replaced in-line fuel filter.
I've not tested the Pickup Coil, but from what I understand that's a all or nothing part... (It will either start or not.) I know I need to replace the EGR Valve... I don't think this would cause this problem would it? I could see it causing rough idle, but not a hard start. Next to check, 1. IAC Valve - Clean and inspect... if good put back or replace. 2. Re-check spark plugs to be sure none are loose 3. Compression test - Should be somewhere around 170-180? 4. O2 Sensors - check for carbon buildup. Check with multimeter - No voltage when cold. Heat them up and I should start to see voltage. 5. Coolant Temp. Sensor - I read to test this by taking an ohm reading while cold, let the temp of engine to up then test again. If Ohms are lower, then the sensor is good. 6. Injector Ohm Test (I understand I should see 14 ohms or less... Correct?) 7. Injector listening test (I should hear a consistent ticking noise...) 8. Clean Intake manifold (This winter) Am I missing anything? |
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Posted on: 2011/7/6 23:13
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| Fredbird | Re: Rough start/Sometimes rough idle | ||
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Senior Guru
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Fixed it! Starts and idles better now than I've ever seen her do.
I ended up replacing Cap/Rotor, ICM and Ignition coil. What's strange is everything either looked (cap/rotor) or tested as good (coil/ICM) I will keep her on a short leash for a while, but I think I got the problem nailed down this time. My bet on the problem is the ICM was good enough to test as good, but could not sustain any load when the engine started. Also this is the same part that had the melted connectors. It makes sense as to the idle issue since your est is controlled by ICM, it could have been sending the timing all over the place. Coil may have been good, but I don't care. Everything is new in the ignition line and she's alive again. |
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Posted on: 2011/7/8 19:14
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