Good afternoon everyone,

I'm new to this forum but active in a number of other forums for different vehicles. I have been reading 100's of posts trying to find the same symptoms I'm seeing in my son's car. For his first car we bought a 1986 IROC with a 305tpi motor. It has approximately 33k miles on it and has been sitting in a shed since 1991. The previous owner did replace the fuel pump before i bought the car with a Delco pump (sounds like a mistake). My son and I have replaces all the fluids, plugs, wires, cap, rotor, filters, tires, R34a conversion, and brakes. We have had a great time working together on the car trying to get it back on the road and making it reliable for him to drive to High School. Things were going as planned until just recently. I took the car to work one day trying to get some miles on the car and to bring all the fluids up to temp. The car ran great until I was driving it home that night. It was a hot day, 95+ degrees. I took off from a stop light after driving it down the interstate for about 20 miles and the car wouldn't rev over 3500 rpm. I didn't notice any black smoke and/or any sputtering or backfiring. The car simply wouldn't rev any higher. I pulled over thinking maybe my TV cable was loose and it was a transmission issue. The cable was tight. I got back in the car and drove it back to the shop and after sitting for a few minutes the car wouldn't rev over about 2000 rpm. Again, no smoke or backfires...it simply wouldn't rev higher. All the gauges looked to be good, the car wasn't hot. Once i got home I couldn't see that anything was wrong and my son continued to drive the car without too many issues. Since then a few weeks has passed and just recently my son and I took his car on about a 40 mile drive, mainly highway. It ran fine going there but on our way home, while cruising down the highway (cruise was on) at about 65 mph, the car would just lose power. It would kick off the cruise control and just coast as it felt like the car had died...then, after maybe a minute, it would pick back up and run again and maintain speed. This time, when i got home, i left the car running in the shop and took off the gas cap. I was amazed at how much pressure was in the tank...it made a very loud hissing noise that went on for maybe 20 seconds. Once the tank was fully vented the car died. Once the car died it wouldn't start again until i set it set for maybe 5 minutes. This was Friday. On Sunday my son took the car out as i told him the problems were related to driving the car long distances and around town it should be Ok. He took the car and drove around town maybe 15 minutes. The car died on him a few times and, for the first time, the check engine like came on. I told him to park it, which he did for a few hours, and then drive it home. After a few hours the car started fine and he drove it home without any problems. I should also point out the noise from the pump. This thing is loud and not consistent at all. There are times we don't hear it at all and there are other times it howls so loud you can't hear anything but the pump. I need to do something different so any advice on the best drop in replacement pump would also be very useful.

As i said before, i have read so many posts about pumps and vents and boiling fuel it has made my head spin. But, i haven't seen a post, at least not yet, that describes what this car is doing at high way speeds...or while trying to rev over 3500 rpm.

I apologize in advance if there is a post out there matching mine and i didn't find it...i don't like being one of those guys that doesn't do enough research before i waste anyone's time.

Thanks to everyone that has read this and for any advice or help...it is much appreciated.

Greg

 

You're probably on the right track. It would be nice to have a fuel pressure gauge on it when this happens, though.

Did you retrieve the error codes from the computer when the SES light came on?

Do you know if the tank was flushed out when the pump was replaced? It's almost always standard, but was the pump pickup sock replaced when the pump was replaced? For a car that sat that long, it wouldn't be surprising that crud built up in the tank that is now being loosened up with fresh fuel, clogging the pickup sock, and/or getting into the pump and killing it. Working when cool but not when hot is also a symptom of a failing fuel pump. The pump sound not being consistent isn't a good sign, either.

 

Sounds like vapor lock ,

but this could also be caused by a clogged / restricted

fuel line
return line

Debris in the gas tank can be clogging the pump sock / fuel pump pick up line

Clogged fuel filter

I would be inclined to check all the fuel lines for rust / debris... blow them clean or replace

Inspect the fuel filter.

Same with gas tank... I would not take the seller's word

The factory pump is a "AC / Delco" part, that does not mean he replaced the original unit. Drop the tank and check it may be worth to have the tank boiled out or replace with a new one.

 

Thanks for the reply Five7Kid,

I have not checked the codes when the light came on. After the car sat for a few hours the light went away and didn't come back on. I will see if the codes can be retrieved through.

I'm not sure what the PO did when he changed the pump. I assumed it was all done correctly. I found it interesting though, he specifically said he ONLY used replacement AC Delco parts. I have a feeling i'll be pulling the tank soon, which sounds like a fun project in a garage without a lift.

Thanks for the reply

Greg

 

FRMULA88, thanks for the reply.

I recently put in a new fuel filter and was alarmed by the black gunk (if that is a word) that came out. I'll put another filter on it just to be safe and I'm assuming it isn't too hard to blow the lines out so i'll do that at the same time. I'm not suspecting this to be my smoking gun though because the problem i'm having is only when its hot and after a drive of more than 30 minutes or so.

Thanks again for the reply

Greg

 

I'm having very similar issues. Almost exactly the same. Found this on the forum...

"Re: Fuel Pump Issues regarding heat???
Well, I finally believe I know EXACTLY what is causing the heating/stalling issue. Finally! I recently had my Iroc dyno'd down in Georgia and while I was there I had them adjust my timing and fuel pressure to get the best run possible. Put down 215rwhp, 305 with a small .471 lift cam, headers, and cat-back! Well immediately after that my car started having the heating/stalling issues (even though my car never goes over 190* even in traffic). So I pulled the pump (thank god for the trap door mod!!) and found that the rubber fuel line coming off my Walbro 255 had shrank by almost an inch and was sitting on top of the pump outlet! I couldn't believe it would crank and drive! I believe the ethanol mixed in today's fuel had something to do with the massive shrinkage. So I put a new "longer" fuel line on the pump and new sock. I put it all back together thinking I've got it all fixed, but the problem was still there! No change at all!! So I pulled everything back apart. Pulled the fuel filter. Pulled the lines off the fuel rail and blew compressed air through all the lines. This is very messy so be careful. When I tried to blow out the fuel rail, I couldn't get any air to pass through at all. Hmmmmm.... If air can't get through, how can fuel?? Then I started thinking maybe my new BBK adjustable regulator was bad. So I hooked all the lines back up to the pump and fuel rail. I pulled the connector off the fuel pump relay and jumped power to the pump. With the pump whining loudly I could hear strange noises very faintly coming from the fuel rail. So I loosened the regulator adjuster screw and WHOOOSH! I could hear all kinds of fuel flowing through the rail and the pump whine was GONE!! Took it for a test drive and OMG the power difference was amazing! But anyway, the gist of the story is that yes the fuel pump was overheating due the strain of trying to hold pressure in the system with no flow. Topping off with cold fuel allowed it to pump longer under the strain. The muffler under the tank has NOTHING to do with it (which I knew all along, come on, it's obvious!). Tank pressure has NOTHING to do with it. Too much pressure only helps the pump do it's job and reduces vaporization. Too little pressure doesn't affect anything. I had removed my charcoal canister a LONG time ago and just left the vent line open with no problems. Basically, anyone who is having this specific problem of driving fine for a little while with great power and then slowly losing power (along with increased pump whine) until it cuts off is having one of two problems, possibly both:

1. Bad pump, replace. If stock then buy el-cheapo with a lifetime warranty!

2. Partial or Full blockage of the return or feed line.

Oddly enough, my pressure was adjusted using a guage and did not spike even though the return line was nearly closed off. It was adjusted to 43psi. Either way, I have no more issues with pump whine or stalling regardless of heat. I still put a new fuel filter in and some fuel injector cleaner while I was working on things.

I really hope this helps a lot of people, because until now, I've yet to hear of anyone post a definitive cause/solution for this problem. Good luck!

Sent from my iPadu"

Now, I have not got to try this yet but I hope this fixes the problem. I have read a million posts on this problem and this is one that claimed to find and Fix the problem.

I found some other posts, I will try and find and reply with those too.

 

Found this one too...


"Quote:
Originally Posted by Chevy86 IROC-Z
Sure. I already has the walbro FP. So I threw that in along with the fuel return line diverter disk, blew out the lines, changed fuel filter, and wrapped the lines next to the exhaust manifold. Done deal. So I'm not sure what fixed it.
Congrats man! I'm glad you've got yours finally fixed! For the rest of you still having this problem, here is a simple complete fuel system overhaul procedure that will almost certainly fix your hot stumbling problems:

1. Replace fuel pump (even the cheap ones work fine, people just kill their new one most of the time because they still have restricted fuel lines and this overheats and kills the new pump over time)

2. Blow out the feed and return lines, the sending unit, and fuel rail with compressed air (if air will not blow through your fuel rail then replace your FPR).

3. Replace the fuel sock (usually comes with the new pump) and in line fuel filter.

That's it! Your car will drive exactly like it did in 1985! You don't have to add the fuel diverter at the end of the return line, but it won't hurt anything to have it. You don't have to wrap your fuel lines. I didn't, and I have un-coated headers with no problems and the fuel lines run within a 1/4" of them at the frame rail. And of course, during your fuel system overhaul procedure, don't forget to check all your fuses, grounds, and wiring associated with the fuel pump to make sure it's getting proper voltage.
Sent from my iPad"

Maybe these suggestions will work.

I am going to try these and I will post here what I find. If you decide to do this also, let us know.

Apparently this is a common problem that many suspect is a build up of several different problems creating one big one.

 

Found this one too....


New canister in (GM Part number 17092109) whcih also came with a solenoid. Had quite a bit of hot air escaping the same air port, BUT NO FUEL VAPORS. Drove it for a couple hours and it's just over 1/4 tank now. No boiling gas, no fuel vapors anywhere and the tank had pressure like it should without wanting to blow the cap off in my hand. Outside temp was right at 100* today. I feel comfortable my issues are resolved, but will drive it around the neighborhood for a while to make sure it doesn't die after operating at 220* for a while. Here is the list of parts that were replaced and why with part numbers in parens (for a 91 Z28 5.7):

1. Racetronix Fuel pump and Hotwire kit - Fuel pump was whining after about an hour of driving or when it got hot
2. Fuel Tank Sending unit (19111386) - frozen rollover valve in the closed position (Also replaced the sending unit lock ring (25124032)
3. Canister pressure control valve (17087240 but From Oreily's Auto Parts) - Wasn't venting the tank to the canister when under pressure. Caused the tank pressure relief valve to open causing fuel vapors in the rear.
4. Canister (17092109) - Fuel vapors escaping from the air port when idling
5. Fuel filter - because I was there and it's cheap and easy.

I had multiple issues that added to to a large headache. Will keep you posted if anything else happens.

--Edit--
Drove it more today during the heat of the day and got down to 1/8 of a tank with no issues.
Sent from my iPad

Not sure this one will help, kept it thinking you never know.

I think the common denominator is the congested fuel lines. That will be my focus, especially seeing how you have already discovered blockage in your fuel line.

Let me know what you find out.

 

We had a lot of the same issues on 84 carb. Change fuel filter and car would run great for couple months (not very many miles driven). Then would start to die trying to get it to highway speed. Cut open fuel filter and was completely packed with rust. Had to replace the tank and sending unit.

 

IT'S NOT VAPOR LOCK!

You need to understand what "vapor lock" is. With a pump up by the engine, it has to suck on the pool of fuel in the tank. The pressure to do this is provided by the atmosphere. The pressure in the fuel line between the tank and pump is at a lower pressure than atmospheric, which lowers its boiling point. Since fuel supply lines typically live in a hot environment, and systems that only pump as much fuel as the engine is using (no return line), the combination of low flow, high temperature and lowered pressure can cause the liquid to change to vapor. Fuel pumps don't pump vapor, and even if they did, vapors don't work correctly in a fuel mixture system (i.e., carburetor) designed for liquid operation. Hence, what's called "vapor lock" which causes the engine to lose power, run poorly, or die.

3rd gens ALL came with a return line to help reduce the possibility of vapor lock (increased flow through the supply line reduces the time for the fuel to pick up heat, and keeps cooler fuel flowing through the line). The factory also had a "vapor lock kit" for carbureted engines that added an in-tank electric pump to push the fuel up to the engine-mounted mechanical pump, and increase fuel flow further.

However, all of that applies carbureted engines, and the OP doesn't have a carbureted engine. And, to summarize, a fuel system with a pump in the tank CANNOT VAPOR LOCK! It simply cannot happen. With an in-tank pump, the pressure in the supply line to the engine is higher than atmospheric, which raises the boiling point of the fuel. And, typically, and certainly for the factory system, will have a return line to maintain a constant flow of fuel through the supply line.

"Black gunk" in your fuel filter is exactly what I was talking about. You might be able to put a fuel detergent in the tank to clean things up, but you'll probably be changing the fuel filter several times before it's cleaned up, and there is a high likelihood that you will not clean up the pickup sock, and also a high likelihood that you'll ruin the pump in the process (assuming it isn't already).

 

Like I said, the common denominator seams to be blockage in the fuel lines.

 

Awesome analysis, but I think the fuel lines can be just as much at fault, especially for a vehicle that has sat with old gas for a while.

Basically, plus the fuel lines and the fuel rails, fuel injectors, etc...

Like I said, I am having the same problem and I will fix this, thanks to the people on this forum that give of their personal and professional advice, like five7kid and others here.

I joined this forum knowing that I do not know all the answers. We all joined for the same reason, to share knowledge and experience.

 

I said it "sounds like vapor lock" but if you read my post its most likely due

to a restriction in the fuel lines..

if the return line is clogged... it will exhibit the same symptoms as vapor lock..


You also can't expect a 25+ year old gas tank & fuel lines to still be in pristine condition, especially if left "dry" in a unconditioned space... condensation would have rusted the inside of half empty fuel tank fuel lines etc.

the rubber sections of line would also dry up.. now add fuel with 10% ethanol which was not around in 1985... and you have black slime... because the rubber hose is not compatible with the ethanol..

The best thing for long term storage of old cars is to keep the fuel tank "full" this will prevent condensation and avoid a lot of these issues.

Improper storage does more damage than driving them ! But what do I know I only had my ride for 20 years.. when my kids were born and I was busy with the family & remodeling the house my car sat for 18-24 months in an unheated garage... but I took the steps to "moth ball" the car so no issues.

 

I dropped my tank at home without a lift many times, just get a good set of jack stands & get the car as high as possible.

3rd gens take a bit more effort because you some stuff to move out of your way before dropping the tank.. (muffler, heat shield, panhard bar..)

The filler neck is brazed to the tank, make sure you remove the fuel filler door splash/overflow shield & fuel cap so you have room for the filler neck to move when you drop the tank.

The big advantages to in-tank pumps are:
Quiet, because the pump in the tank and submerged in fuel may hear it prime.. but when the car is running you not hear the pump..

Service life.. because the pump is submerged in fuel it should never overheat so it lasts a long time.


Disadvantage: it's in the tank making servicing a PIA ! LOL !

 

my next remodeling project will be the garage... and there will be a 4 post lift !

LOL

 

Thanks to everyone that has replied with their advice and opinions!! Don't want to bore everyone with detailed 'thank-yous' for all the posts but they are all appreciated!!

I'm hoping in the next few weeks to have the tank dropped and I'll start with a new pump. Before I do that I will check the fuel pressure but even if the pressure is good I think i'll still put in a higher quality pump that makes less noise. This will also give me an opportunity to check the cleanliness of the tank etc. When i change out the fuel filter I'll blow the lines out at the same time. It seems, after reading all of the similar posts, I might have a combination of things going on with my car. The pump sounds like a concert, even if it is working correctly I want it changed. I think I might have a block in my canister/vent because the tank builds what I'd consider to be a tremendous amount of pressure. I'm thinking after I replace the pump, clean the tank, and replace the filter...if still have the problem, it has to be because the fuel is getting too hot and I'll have to investigate that after I have eliminated all the above items as potential problems.

Thanks again to everyone!! These forums are great and all the advice and personal experience is very helpful and makes working on these older cars much more enjoyable!!

Greg

If

 

keep us posted when you have it sorted it out !


hopefully a little TLC and some clean parts is all you need.

 

Thought I would post what I have found so far on my (new to me '91 Z28 5.7).

Pulled fuel filter, dark brown (rust) colored gas drained from upstream (gas tank side).

Pulled fuel pump, packed with fine rust debris. The sock did no look like it was catching much.

The gas tank has a lot of surface rust.

Think I'll try the '94 gas tank recall. Regardless, new tank,fuel pump and filter.

Hope that works. "Hope is not a plan".

GoJoe

 

Keep me posted GoJoe how the car runs after your changes. I'm hoping to work on my car this weekend.

Thanks and good luck!!

Greg

 

Forgot to mention, tried blowing thru the filter and could barely get air to pass thru, until I blew through the other side. Oops, made a mess.

I'll keep you posted. Please do the same.

 

See posts 2 & 3
looks like you found that "smoking gun".

 

Update...
Yep, blew out the line from tank to filter, replaced filter, cleaned the fine screen on bottom of pump and replaced sock.

Have driven it about 80 miles with no problems. Lined it up against my 2013 Chevy Malibu (2.0 turbo auto), and I was barely pulling the Malibu (maybe) up to 100 mph. Really it was a rolling start at about 45 mph to 100.

I'll get a new tank soon. Amazing what they can get out of a 2.0 these days.

 

Good afternoon gojoe,

I started a different thread on what I have done to my car that has my update. I typed/copied a lot but so far the changes i've done have made a significant difference!!

https://www.thirdgen.org/forums/tech...placement.html

Good luck!!

Greg

 

I know you started a new thread but, what's the latest in your world?

 

Hey gojoe,

Not a lot is new actually. Since we've put the new pump in the car has ran great!! The pump is still quiet and it hasn't stalled yet. We don't drive the car much though and not sure we have taken it farther than maybe a 10 mile drive at one time so I can't say for certain we are out of the woods yet.

Did you make any of the changes to your car?

Greg

 

No not yet. But I am certain. Took it to auto cross after fuel pump and filter replacement. Lasted through 5-1:15 minute passes. Started same loss of throttle. Pulled fuel filter, and "oh my", never seen so much rust!

By the way, I drive this car about 30 miles each day to work and back. Cruises fine.

I have replaced the fuel filter almost every other week. Endless rust.

I will replace gas tank or repair. Decisions, decisions.

 

When you last replaced the fuel pump how did you clean out the tank? It was difficult to clean mine but tried to the best i could. I would dump some fuel in it and scrub...try to rinse...and repeat until my forearms hurt!!

It sounds encouraging, to me, that you are able to cruise to work for 30 miles or so without any issues. How hot is the weather in your area? I still worry that i experienced a fuel boiling problem but not sure if that was simply related to ambient temperature or also the result of poor performance from my pump?? Verdict is still out and we might not know this answer until next summer as fall is quickly approaching in Kansas.

Good luck with whatever decision(s) you make!!

Greg

 

well i found my project for the weekend thanks you guys for this great write up

 

Rockyd,

Not sure if you checked out the link I had from above. It has an update on what i did, step by step. Most of the steps are self explanatory but I did find it helpful. I had my 16 year old son do most of the work while i watched and drank beer. Well, that isn't true...i did help...but his knuckles were bleeding and not mine.

Good luck!! If you have any questions don't hesitate to ask, I'll help any way I can.

Greg

 

Thats a really great write up. I have done it before and wish i could drink beer watch my son do it but i still have a few more years for that hahaha. on this car some one did the hack cut the top part off so im going to have some fun with that and hope it works out for me. thanks and appreciate the offer for help as i will keep you at hand.