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| TommyT-Bone | 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
 
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I checked the power to the relay,12+v, checked the fuse, replaced the relay. Still wouldn't start. I tapped the fuel pump with a wrench and checked some wiring up under the hood.. Went and turned the key and the pump energized.  Shut the car off. Wouldn't restart. Fuel pump did not energize. Let the cat cool off. Tapped the pump again. Went back about 5 minutes later the pump energized. My question is The wiring on the relay comes from where. There is a hot and a ground and three other wires. What components are involved in getting the pump to charge? The ignition? (It's not very old and lightly used) What else? How hard is it to change a fuel pump on 91 Vert. Everything can be seen by removing the back license plate. The dealership said something about a communication error. Possible ECM, CCM issue. I think it's the fuel pump. Thoughts? I pulled it out of the dealership at no charge to us for their failed diagnosis. Thanks in advance. |
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Posted on: 2013/8/10 23:50
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| josephf31 | Re: 91 Corvette Convertible fuel pump issue | ||
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Senior Guru
 
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Not sure on your cause but it's pretty easy to change the fuel pump. |
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Posted on: 2013/8/10 23:54
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| joeld | Re: 91 Corvette Convertible fuel pump issue | ||
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Guru
 
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Not sure of the wires on your 91, could be the same as a 89 but I would have to check.
As far as replacing the pump, it's a easy job. I could, along with many other folks here, write it all ou. But instead here is a good set of instructions and some decent pictures. Joel http://www.corvettemagazine.com/tech- ... ending-unit-installation/ |
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Posted on: 2013/8/11 1:22
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
 
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All I have is a 91 FSM but, I'll bet they are close wiring wise. But my first question is, You tapped the fuel pump with a wrench? The fuel pump is inside the gas tank. I'll question the dealership a bit cause the fuel pump relay gets turned on 2 ways. First is by the ECM which energizes the relay thru the dr.green/white wire. This will stay energized as long as the ECM sees ignition signals. IF the signals are lost but you have oil pressure, the fuel pump is energized by a red (hot) wire from the oil pressure switch. After verifying that there is power to the relay (which you did), you can jump terminals 1 & 4 with a fused jumper and the pump should come on (this needs to be checked with a 91 FSM though). You could also pull the pump and check for power at the pump connector (but don't run the pump for more than a few seconds out of the tank). Note that a 92 has 2 fuel pump relays (not sure about a 91). If it was me, I'd be pulling the pump for inspection and electrical diagnosis. |
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Posted on: 2013/8/11 2:23
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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Thanks for the info. The red wire is hot. There should be sufficient oil pressure. The relay I replaced was the one by the tank. I know throwing parts at something is the wrong approach. That's probably why I do it. I have meters but auto electric isn't my strong suit. What I tapped was next to the relay ground on one side an a brass fitting with hose on the other side. It could well be an ECM comm error. I'm going to go through the FSM but reading from a hands on perspective helps me to process FSM steps better. Thanks for the link Joel. |
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Posted on: 2013/8/11 3:35
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
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Hummm, check the FSM for the relay location, it will be in the back of the book under Component locations.
Both 92 relays are under the dash. Tapping the hose and the pump coming back on may indicate a bad ground of connection to the pump (or the pump itself). |
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Posted on: 2013/8/11 3:44
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Tommy -
As far as I know, the fuel pump relay for the 1991 is located under the dashboard in a 5-row bank of relays: http://www.corvetteguruforum.com/modu ... ewtopic.php?post_id=44904 I find relays either work or not, usually not intermittent - but I have seen really old ones that must have had corrosion that didn't work until I tapped on them. I believe there is a delay on my 89 if you turn the car ignition on the fuel pump energizes, but then if you turn if off and turn it back on immediately it doesn't. I don't recall exactly. So if you are suspecting the fuel pump the #1 diagnosis point is to check the fuel pressure at key on and when cranking and running. If you are getting zero fuel pressure then you have 1) bad pump 2) power problem to the pump 3) fuel delivery problem. You can manually turn on the pump by running a 12v power line directly from the battery to terminal G on the ALDL connector.  Run those tests and let us know. Matthew |
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Posted on: 2013/8/11 22:36
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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I checked the 89 fsm and it made no reference the the delay. It said basically once the ignition is turned on the ecm sends a reference signal to the fuel pump relay to energize. It will run for approximately 2 seconds and monitor for injector pulses. If there are no injector pulses, the ecm cuts the signal to the relay. It does say in the flow chart, however, when testing to wait 10 seconds before turning on the ignition between tests. I don't know why, maybe that's what I was thinking of before. |
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Posted on: 2013/8/12 1:22
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
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Quote:
I checked the 89 fsm and it made no reference the the delay. It said basically once the ignition is turned on the ecm sends a reference signal to the fuel pump relay to energize. It will run for approximately 2 seconds and monitor for injector pulses. If there are no injector pulses, the ecm cuts the signal to the relay. It does say in the flow chart, however, when testing to wait 10 seconds before turning on the ignition between tests. I don't know why, maybe that's what I was thinking of before. [/quote] Same with a LT1 except the ECM monitors the low res. opti pulse. Of course if you then get oil press, it will activate the relay separately from the ECM. |
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Posted on: 2013/8/12 3:40
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Quote:
 Same with L98. |
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Posted on: 2013/8/12 11:37
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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I'll get back when I have some playtime. |
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Posted on: 2013/8/12 21:23
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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The fuel pump did not manually turn on when 12v applied to terminal G on the ALDL connector. |
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Posted on: 2013/8/16 19:26
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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This is what I believe to be the fuel pump. Do 91 Corvettes have 2? One in the tank and one out? Just wondering. Here are a few pics. The relay I replaced in white and the fuel pump secured with metal clamps to a plate bolted with two bolts to a metal frame.
Attach file:  IMG_1263.JPG (60.61 KB) IMG_1264.JPG (61.36 KB) IMG_1265.JPG (57.08 KB) |
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Posted on: 2013/8/16 19:39
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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I'll have to get with my neighbor. I'm sure he has a fuel guage to measure trhe pressure but I'm pretty sure it's low too zero since the fuel pump engages intermittently. I got it started and move it to the carport. After I ran it and warmed it up it would not restart and the fuel pump did not power up (buzz) after that. I can hear two relays click when I engage the key. One under the hood and one in the back. Of course I can't be three places at the same time so I need a helper to listen while I turn the key.
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Posted on: 2013/8/16 19:45
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Posted on: 2013/8/16 19:51
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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Guess I'll have to check the tank for a sending unit/fuel pump too. |
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Posted on: 2013/8/16 19:55
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| josephf31 | Re: 91 Corvette Convertible fuel pump issue | ||
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My '91 coupe has only ONE fuel pump and it's in the tank, replaced by removing the fuel sender assembly from the top of the filler neck. I don't know that the convertible would be any different, have to check the manual.
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Posted on: 2013/8/16 19:56
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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No need to worry. I'm ready to get clubbed with a stupid stick. |
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Posted on: 2013/8/16 19:57
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| bogus | Re: 91 Corvette Convertible fuel pump issue | ||
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Grand Imperial Pooh-Bah
 
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I will express mail you one.
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Posted on: 2013/8/16 21:17
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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I put one in my 90 and this should be no different. Don't you have a blower on your car? Maybe that will need more fuel pressure to run then a stock 190 g/h pump.
Here is what I used....they make a 255 g/h but don't know if you need it.... http://www.racetronix.com/RX-C44-FPKG-2.html Get the Walbro pump if you are going to change it out. Matt has a great how to with pics and I took pics of my install also some where back in the archives of this great forum... |
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Posted on: 2013/8/16 21:28
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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What you talkin about Willis?  I don't need anything fast. What are you sending? |
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Posted on: 2013/8/16 21:29
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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Ya. It's a blown 383. I guess that's some important info there.  I didn't build it so everything is a mystery to me. |
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Posted on: 2013/8/16 21:32
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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I'm not sure what that is behind the license plate is but I'm thinking it ain't stock........I'm also sure they needed more fuel pressure to run that size engine but Matt and the guys would know about that....
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Posted on: 2013/8/16 22:09
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| bogus | Re: 91 Corvette Convertible fuel pump issue | ||
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Grand Imperial Pooh-Bah
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That sure ain't stock... And yes, it's a pump.
I doubt the OEM one is there. Remove the gas cap, remove the rubber plate around the filler neck and check for what wires do what. I am betting big money you have one killer hot pump outside the tank. If you require replacement, Electromotive makes some of the best. Racetronix might have an internal that will do the trick, too. |
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Posted on: 2013/8/16 23:58
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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My next move is pull the pump and give it a once over for make , part # , etc. Might as well take a peek at the tank . The more I look the more I'll know. I'll be back when I find out more.
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Posted on: 2013/8/17 1:06
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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How would you keep that outside pump cool Andy...?
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Posted on: 2013/8/17 1:17
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Tommy, as mentioned above that is not stock. Probably added due to the blower. You need to see it it is a primary pump or auxiliary. Then we can decide the next step.
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Posted on: 2013/8/17 3:15
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Does your fuel gauge still work? If so the assembly is probably in there even if the pump is not. If that's the case I would get a high flow pump and reinstall in stock configuration. But we are getting ahead of ourselves already.
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Posted on: 2013/8/17 3:18
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| joeld | Re: 91 Corvette Convertible fuel pump issue | ||
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I'm curious about the in-tank set up. I'd suggest taking a close look at the supply line coming from the tank, there's got to be some kind of a splice there going to that pump.
Joel |
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Posted on: 2013/8/17 3:52
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
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Bubba pump.
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Posted on: 2013/8/17 5:48
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Yes. |
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Posted on: 2013/8/17 11:38
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Does that car have a wideband installed for tuning? Does it have an in car fuel pressure gauge to check for pressure drop? You need those with a supercharger. Just a guess, but I bet you would be fine with the racetronix 255 lph pump if you can put it back in. The exterior pump you have might be a booster pump, or it could be primary. Unknown until you open up the tank.
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Posted on: 2013/8/17 12:15
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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Quote:
No and No |
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Posted on: 2013/8/17 12:26
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| biggrizzly | Re: 91 Corvette Convertible fuel pump issue | ||
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Very cool Tommy! What kind of supercharger? Pro-Charger?
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Posted on: 2013/8/17 12:34
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Yup. |
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Posted on: 2013/8/17 12:58
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Tommy, if it were my car I would make those items a priority. Figure $500 at least.
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Posted on: 2013/8/17 13:51
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Quote:
Maybe later. |
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Posted on: 2013/8/17 14:32
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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2015 Memorial Day Car Show Winner!
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Quote:
 As finicky as those fuel systems can be I'm surprised you have not had trouble before this....just saying.... Whoever engineered it must have know what they were doing at the time..... |
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Posted on: 2013/8/17 15:03
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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I'm rather surprised myself after what I've read around the web with fuel pump failures. Some after a few months. All I know is that I will do what must be done. (Or hire somebody to do it) I can always pay BillH's round trip airfare, give him room and board and throw him a few bucks.
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Posted on: 2013/8/17 15:40
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Booster pumps are not uncommon with supercharged engines and stock fuel pumps, but afaik they use a fuel management system to turn on. I am guessing this was installed in lieu of the stock pump.
Tommy, to rule out the pump being bad, try to feed power to the pump through the aldl and check for power at the relay. Or pull the pump and manually jumper it while off the car. |
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Posted on: 2013/8/17 19:09
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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All he wants to do is dnbfs. And you couldn't afford his casino tab if that's part of the deal (although he always wins....) |
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Posted on: 2013/8/17 19:10
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| TommyT-Bone | Re: 91 Corvette Convertible fuel pump issue | ||
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Chair-man of the bored
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Quote:
It's not afaik. It's for real. I did feed through the ALDL and nothing happened.(see above) I've already started the disassembly. I'll bench test the outside pump. I have everything torn down to the point that I'm getting ready to pull the in tank sending unit. The pictured pump is almost out. Just a few clamps and wiring connections away. Same thing with the in tank unit. A few bolts and a connection or two away. I'll take and post some pics when I do it. |
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Posted on: 2013/8/17 19:22
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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I love a good what done it....better get some popcorn...
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Posted on: 2013/8/17 22:03
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| bogus | Re: 91 Corvette Convertible fuel pump issue | ||
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Grand Imperial Pooh-Bah
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I am betting money they wired that thing up special... I thought I saw a relay there.
Let us know what you find. I think it's a pro-charger. Take a pic of it, Tommy. |
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Posted on: 2013/8/17 22:43
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
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Quote:
Well you could ......,..never mind. On an intank fuel pump, the fuel sloshing around does zip, zilch, nada to cool the pump. That's an internet myth as is running less than a quarter tank of fuel will overheat the pump, complete bullshit. A booster pump is a bandaid, using a pump with the gpm required for the mod is the correct way to do it. |
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Posted on: 2013/8/18 2:13
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
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The beer tab would be higher than the airfare. |
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Posted on: 2013/8/18 2:15
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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Soooo why are the pumps in the f'en fuel tanks then if its not a cooling issue and not out where we can get at them...?????
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Posted on: 2013/8/18 2:51
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| Matatk | Re: 91 Corvette Convertible fuel pump issue | ||
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Because I keep my fuel inside the tank, not outside |
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Posted on: 2013/8/18 3:29
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| BillH | Re: 91 Corvette Convertible fuel pump issue | ||
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The Stig Moderator
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Quote:
Cause the car companies can save $2 on the assembly line by making them intregal with the gauge sender unit and not inline. Restomods, hotrods and some racecars run inline pumps all the time. |
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Posted on: 2013/8/18 3:44
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| Ultraman | Re: 91 Corvette Convertible fuel pump issue | ||
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You would think the aftermarket guys would develope a system for an outside the tank fuel pump for these Corvettes that you can't get to them without dropping the tranny or half the rear end...C4's at least you can get to.....and some early C5's were service from the bottom of the tank so you could reach it....but not anymore...
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Posted on: 2013/8/18 14:03
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