Diagnostics
Printed From: West Coast Fieros
Category: Technical Topics Forum
Forum Name: Technical Questions and Discussions
Forum Description: Got a technical question about your fiero? ask it here.
URL: http://www.westcoastfieros.com/forum/forum_posts.asp?TID=673
Printed Date: 27 November 2024 at 1:25am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Diagnostics
Posted By: Matt
Subject: Diagnostics
Date Posted: 06 June 2008 at 12:51pm
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My Fiero is still down. I'm going to have some time this weekend to work on it but I need some information to help me diagnose the problem. 1. What should the compression be on each cylinder? (86 Tech4) 2. What is an average/acceptable psi for the fuel line? 3. Is there a way to check if the oxygen sensor is working properly? Hopefully I'll get the car running better this weekend. Its not insured so I won't have it at the car show, but I hope to be there and meet up with some of you guys. ------------- I wanna go fast. |
Replies:
Posted By: Dr.Fiero
Date Posted: 06 June 2008 at 9:08pm
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1: 150+ (even is more important than the actual #) 2: Around 7psi IIRC 3: Not until you get it running. And that won't affect it running or not BTW (the ECM doesn't even look at it for about 60 sec's after starting). |
Posted By: Matt
Date Posted: 07 June 2008 at 12:54am
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The car is running. It starts and idles fine, but violently hesitates or "bogs" through the mid rpm's. Once you get it up to around 3000 she runs clean. Although once on the highway it's as if there is a limiter on the engine as it doesn't pull any harder past 3000. Where as normally after 3000 the car takes off and pulls VERY strong. I just hope it's not that stupid fuel tank sock, or the pump itself. I had no idea how I'd change those. ------------- I wanna go fast. |
Posted By: Matt
Date Posted: 30 June 2008 at 12:07pm
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Had some time to work on the car yesterday. The car seems to be
having a difficult time starting, but if I drip 2 table spoons of gas
into the TBI she fires up right away. If I disconnect the vacuum line
from the map sensor the car runs perfectly for 30 seconds and then
starts to run rough. If I leave the vacuum line on, the car runs rough
for the first 30 seconds and continues to run rough. Does this mean anything to anyone? ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 30 June 2008 at 6:17pm
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You're running really lean. Pulling the MAP sensor line off tells the ECM (falsely) that you've got the gas pinned to the floor, or more accurately, that you've got an extreme load on it. So it dumps in more fuel. I say you've got a gimped TBI unit, injector, or the filter sock is clogged, or the pump is trashed, or the filter is clogged, or.... shall I go on? |
Posted By: Matt
Date Posted: 30 June 2008 at 10:39pm
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It was running perfectly until I stopped to get some gas and then 20 seconds later it started acting up doing the things previously mentioned. I'll try some more things and post what I find. ------------- I wanna go fast. |
Posted By: Matt
Date Posted: 13 July 2008 at 3:54pm
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Just checked the fuel pump by installing the pressure gauge in the fuel line before the fuel filter. The first time the key was turned on it pressurized to 25KPA or 3.5psi, then dropped, and the next three times it pressurized only to 20KPA or 3psi, then dropped. Is the low fuel pressure most likely my problem? I'm going back out the check the compression of the engine, I'll post my findings when I'm done. ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 13 July 2008 at 4:03pm
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3.5psi is WAY low - and it dropping rapidly off tells me you're bypassing fuel through the regulator (which would also explain the low pressure reading probably). Probably the easiest solution here is to swap out the TBI unit with a known good one (the pressure reg is integral BTW). Someone around here must be scrapping a duke.... You're 86 right? AFAIK, 84/85/86 are all the same. 87/88 are different. |
Posted By: Matt
Date Posted: 13 July 2008 at 4:07pm
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I don't understand. I tested the fuel pressure before it even reached the TBI, which says to me the problem is the fuel pump. If you're mostly sure its the intake the is the problem I know where I can grab a Holley TBI for an 86 Fiero. ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 13 July 2008 at 4:19pm
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If you want to go one step more easily - clamp off the rubber return line, then pressurize the system again. The pressure should go WAY (!!!) up - maybe 40psi or more. That'll tell you how alive the pump is. |
Posted By: Matt
Date Posted: 13 July 2008 at 4:52pm
 Ok, I'll go and try that right now, although my gauge only gets to 10psi or 70KPA. I'll post the results.
------------- I wanna go fast. |
Posted By: Matt
Date Posted: 13 July 2008 at 5:07pm
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I assume the rubber line that connects to the fuel filter is the "fuel line", and the "return line" is the other rubber line that runs parallel to the fuel" line". With the "return line" pinched with a vice grip, and the fuel pump pressure gauge placed in the "fuel line" right before it reaches the fuel filter it, there was no difference is the pressurization. It built up to 3.5psi and then dropped to 1.5psi So it seems that it makes do difference with the "return line" pinched. I had someone else turn the ignition on, while I kept the gauge input tight to the fuel line.   ------------- I wanna go fast. |
Posted By: Matt
Date Posted: 13 July 2008 at 8:29pm
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Does this mean I should replace the fuel pump or the TBI?
------------- I wanna go fast. |
Posted By: Capt Fiero
Date Posted: 13 July 2008 at 8:39pm
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Just replace the pump. If you are only getting 3.5psi on the fuel feed line, replace it. I can't offer suggestions on type of pump for the 4 popper motor. So go with whatever the parts guy tells you to go with, unless you are replacing the entire motor and in that case, go with a V6 and a Corvette Pump. :) ------------- Capt Fiero 88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd. |
Posted By: Dr.Fiero
Date Posted: 13 July 2008 at 9:04pm
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And make sure you only get a DELCO pump... or you might be doing the job again in the next year or less.... |
Posted By: Matt
Date Posted: 13 July 2008 at 11:45pm
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Ok, thanks for all the help. I'll start looking for pumps tomorrow and start reading up on the best ways to remove the gas tank, etc. Thanks again Edit: Is the Fiero V6 fuel pump compatible with the Tech4 setup? I'd like to do an engine swap in the future. ------------- I wanna go fast. |
Posted By: Matt
Date Posted: 22 July 2008 at 3:12pm
Here's what I've got so far. 1. Canadian Tire doesn't stock them or order them in 2. Wakefield and Sperling has a "Delphi" for $69.99 and a "Carter" for $89.99 and the sock for $9.99 3. Napa can order in a "Master" pump for $90.00 I can't find a "Delco" pump. ------------- I wanna go fast. |
Dr.Fiero wrote:Posted By: Dr.Fiero
Date Posted: 22 July 2008 at 5:37pm
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Lordco is a Delco dealer (AC Delco is what your GM vehicle comes with BTW!). Oh, and in answer to your edited post on the last page - no. The 4cyl runs about 1/4 the fuel pressure of the V6. So if you swap engines - you're swapping pumps again. But think how good you'll be at it!  |
Posted By: Matt
Date Posted: 23 July 2008 at 2:41pm
....funny  Thanks for the info. Lordco has one for $85.09 and yes I knew AC Delco was the GM standard. Also as far as I've found "Delphi" is another name for "Delco" Although I'm going to check to see if they are the exact same part numbers. If they are, I think I might try the Delphi pump for $15 less, seeing as I'm just going to have to change it again soon anyways. Maybe I can give you some free lessons on how to do it quickly?  Or maybe you can show me at a tech session in my driveway? Either way, Johan will have to be on the road soon, I'm moving at the end of August!AC Delco = Albert Champion Dayton Engineering Laboratories Co. Johan = Johan van der Smut from Goldmember = My gold 86 2M4 ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 23 July 2008 at 3:48pm
My best time: 19 min's. There's your benchmark.  |
Posted By: Matt
Date Posted: 23 July 2008 at 4:50pm
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That is equally sad, and impressive. Sad that you timed yourself, and impressive if its accurate. Just kidding about the sad part. Any key tips from the pro? ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 24 July 2008 at 7:54am
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tip: Experience helps. |
Posted By: Matt
Date Posted: 26 July 2008 at 5:16pm
That's not exactly what I had in mind.  I bought the pump and sock today so I might start working on it tonight or tomorrow. I'm just going to follow the book unless anyone has some key tips that would make it much easier. As I have enough experience to know, that such tips exist. ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 26 July 2008 at 10:06pm
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Lift up the back as high as you can get it - BLOCK IT UP!!!! Remove the heat shield at the front of the engine bay. Pull the electric connector, and weave it down. Pull all the rubber lines off at the back. Undo the crossmember looking thingy. Undo the T-bolts, then fold the straps out of the way. Pull the tank slightly backwards, then lower the front. Slide it forwards to clear the hoses. Done. I ran into a batch of bad pumps... I was changing it every 3hrs at one point, hence why I was so fast at it. |
Posted By: Matt
Date Posted: 27 July 2008 at 9:38pm
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Hour 3: It's dark now and I can't see anything. I've had the tank off, replaced/re-wired the pump. And put the tank back in. (With 1 jack and 2 jack stands and $20 of gas in the tank!!!) All I have left to do is connect the hoses, and snug the bands. (Tip for anyone doing this in the future, invest in a 1/2" deep socket. Because it sucks to do with an open-box-end wrench.) After 2 showers and a bath I'm mostly clean. (I put up the front of the tank, and spilled out some gas, thus I rolled around in gas and dirt for 30min. I guess we'll see if I did it all right tomorrow. PS: The mechanism which I assume measures the fullness of the tank, aka the float. It registers by moving along a copper accordion band looking thing. Mine wasn't straight. The rear half was further out than the front half, could this be why my tank is empty when my gauge reads 1/4? ------------- I wanna go fast. |
Posted By: Dr.Fiero
Date Posted: 27 July 2008 at 9:59pm
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$20 of gas? So, like... 1/2 gallon? FYI, it's a 13mm, not 1/2" The gauges USUALLY get inaccurate because the resistance in the element changes due to gunk build up. It should read 0-90 ohms through it's full range of travel, and have no spikes or drop outs inbetween. |
Posted By: Matt
Date Posted: 28 July 2008 at 7:03pm
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IT'S ALIVE! My beauty has returned to me. Thank you everyone, especially Dr. Fiero for your help.
------------- I wanna go fast. |