Rough Idle!!
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
Rough Idle!!
Just got the new engine done and fired up. (89'L98 in a 87' roadster). We can't get the idle de bugged. It will run and have to keep giving it fuel to run and I mean rough! The cam,heads bigger valves and ported, and intake system are changed out, along with headers and no AIR, EGR, and CATS. It is sounds like it was backfiring threw the intake and every now and then out the headers. Timming seems on the mark. Could we have vacuum leak, timming? Fuel pressure gets to about 48psi and when we shut it off it the pressure drops. OK GANG can you point me in the right direction. Trying to make FUNFEST on Saturday. Thanks WRO
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
Rough Idle
WE have had a chip tuned by PCMforLESS. The fuel pressure drops of almost right after we shut the engine down. I am wondering if we have it 180deg. out on time? I thought about using propane to check for Vaccum leaks.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Better double check and make sure you're not 180 out....been there, and you'll never get it to idle or run right if you are. How far did the pressure drop? if you have leaky injectors...same problem.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
rough idle
Will check tonight on the timming but the fuel pressure starts out at almost 50psi then hangs in around 46-48 when we try to run, but when we shut the engine off drops to 0 real quick. Any Ideal of fixes?
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Originally Posted by wro87
Will check tonight on the timming but the fuel pressure starts out at almost 50psi then hangs in around 46-48 when we try to run, but when we shut the engine off drops to 0 real quick. Any Ideal of fixes?
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
you need to find the cause of the pressure loss....follow the trouble shooting chart, I'd probably ohm the injectors first, that will tell you the health of the coils, pull the vac. line off the fuel pressure regulator and look for signs of fuel. The pressure on my 87 dropped a few #s to around 37, and held for at least 1/2 hour, I figured good enough. So, it sounds like you either have leaky injector(s), a bad fp regulator or a bad check valve or pusator in the fuel pump.
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Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Yes, you will need to find out where the fuel pressure is leaking at, first. Make sure your at #1 TDC and that the rotor is pointing at #1 cylinder. Also the EST wire will need to be disconnected. But, find the pressure leak, could be the cause of the problem.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
Thanks for all the info gang. We did not see any obivous or heard any fuel leaks around the engine last night but will check again. Before we swapped the engine out, it other ran fine(except for the low in knock)as far as fuel went it would idle just right but would knock like HG#%*(% when you ran it up and then continue at idle. On the EST wire my FM didn't say anything about it when checking the timming. just attach the wire to #1. Will keep looking and hope to figure it out. Thanks
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
On all our l98s you have to unplug the EST to set base timing. Once you've set the timing reconnect it...it may have thrown a code, just pull the negative bat. terminal for a few minutes. If you recheck your timing with the EST connected it will read around 20+ degrees advanced.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
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From: Louisiana
Originally Posted by Da Mail Man
.a bit off topic..rick, can a mis adjusted or dirty iac cause a hard start?
Safety Car
Joined: Jul 2004
Posts: 3,835
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Originally Posted by RRT vette
I believe it can Mail Man. If the IAC passage is dirty or the IAC/ECM is not working together to make the neccessary steps/counts it will cause a hard starting situation.
...now, for the monkey wrench; if the iac were dirty cutting off the air, why would i have a steady idle?.....if i hold the pedal to the floor would that not tell me that the car was NOT getting enough air on start-up?.....if the pedal was not touched and the key turned, the car should start up almost immediately but does not......yes, i know about the csv valve (1988) and the temp switch under the tb...but, don't think the problem is there as this happens when hot or cold......damn, i think i just hijacked this thread!....
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
Rough Idle
OK gang heres what we have found so far. #1 injector was leaking down BAD, found fuel dripping out of the collector on the headerand when pulled the plug this was wet! Tried it out again and the pressure would hold but soon dropped off you could hear it slowly bleed off. Just what should the resistance reading shoud be I could not find it in the FM? So I went and changed all the rest of the injectors out this worked it is holding pressure around 42#. I was able to replace them all by just removing the plenum and not the runners took a little over 2hrs. Now My next ? is just where is the EST according to my FM it is the 4 wire lead that goes into the HEI dist. I just cant believe this is it since it is a real PIA to disconnect(had to take the cap off. Ran way out of daylight and could not try it withthe hopen headers my neighbors might wonder. My IAC is real clean looks new and it measured the correct length.
Safety Car
Joined: Jul 2004
Posts: 3,835
Likes: 30
Originally Posted by wro87
OK gang heres what we have found so far. #1 injector was leaking down BAD, found fuel dripping out of the collector on the headerand when pulled the plug this was wet! Tried it out again and the pressure would hold but soon dropped off you could hear it slowly bleed off. Just what should the resistance reading shoud be I could not find it in the FM? So I went and changed all the rest of the injectors out this worked it is holding pressure around 42#. I was able to replace them all by just removing the plenum and not the runners took a little over 2hrs. Now My next ? is just where is the EST according to my FM it is the 4 wire lead that goes into the HEI dist. I just cant believe this is it since it is a real PIA to disconnect(had to take the cap off. Ran way out of daylight and could not try it withthe hopen headers my neighbors might wonder. My IAC is real clean looks new and it measured the correct length.
Thread Starter
Burning Brakes
Joined: May 2006
Posts: 857
Likes: 1
From: Morrisonville Illinios
Thanks alot will check it out when we get home this afternoon. I just could believe it was the bundle from the dist since we had to take the cap off to unplg it and I was giving GM more credit than that for something so simple. My 87' factory manual must be off a little because it sure don't show the one wire for the EST. In faft it does talk about it under the distribuator but had to go back into the wire set up to find what they were talking about and it showed the 4 lead flat plug in several of the diagrams. THANKS ALOT FUNFEST IS COUNTING DOWN. 