1989 454 Vapor Lock Issues...and what I did..

Tim Traveler · June 29, 2014, 11:19 AM

Hi Everyone:
Not sure if there may already be a thread started on this topic, but I wanted to post some hopefully useful information. I was having some vapor lock issues on my '89 Allegro 454. Sometimes it would act up after running a few miles down the road, especially on hot days. It would start hard, hesitate, stall, etc. I knew it had to be vapor locking. I'd already done a complete tune-up, rebuilt the carburetor, changed all vacuum hoses, flushed cooling system - you get the picture.

What happened one day after I stopped at a store (it was very hot and humid out - about 90 degrees or so) and it wouldn't start until about 30 minutes had passed. As soon as I got back home, I changed out the 195 degree thermostat to a 160 degree t-stat and haven't had the problem since. (I had just flushed the cooling system and had put in the 195 t-stat, so no, it wasn't old & stuck) There's a big difference on the temp. gauge as well. I don't think the lower degree t-stat is going to be a problem - I don't run the camper in the winter, so dash heat isn't an issue for me. It sure seems to make all the difference in the summer. I know these engines run pretty hot in these big class A's, air flow around them to cool them is limited, so any help for it like a cooler thermostat is going to make a big difference....in my opinion.

Thanks for such a great site - there's a lot of great information here and lots of great people too!

Rickf1985 · June 29, 2014, 11:37 AM

It will be a problem because your engine will never get hot enough to boil out the normal condensation that builds up in it. Who remembers the white milky gunk on the bottom of the oil cap? That condensation mixes with the combustion byproducts in the oil and forms acids which in turn do nasty things to the bearings and other parts in the engine. That is why all engines went to 180 and then 190 thermostats as they progressed through the years. The hotter an engine runs the more effeciently it runs. The main problem is, as you have found out, the fuel issue. That is why on the newer fuel injected engines in cars they have 212 degree thermostats. A pressurized system along with antifreeze will not boil until 240 or so.

GONMAD · June 29, 2014, 12:22 PM

You are correct SIR! The 195 is now the accepted temp for most engines but I prefer a 180. As far as the vapor lock try an electric pusher or lift pump in the rear. This will stop the problem usually. It does not have to be high pressure but this stops the problem. Remember that volume is an issue so don't use anything less then 3/8" fittings & lines. Keep the pressure around 3 to 5 lbs. I also remove the shrouds along the sides of the engine for two reasons, First it makes everything more easily accessible & second it allows more airflow overall. Also if you don't have one or two FANS for the radiator, get extra cooling from their use. Arrange the fan to come on with the key from a relay hooked to a switched source. Mine runs always on. This takes the demand from the clutch fan & extends it's life & you don't have to listen to the noisy thing as much. Another item to try comes in a few different brands is KOOL & Water wetter products are good for keeping things a bit cooler. These things seem to ALWAYS run hot so anything you do to keep it cooler is a welcome fix. Good luck in your endeavors. As Always C YA! GONMAD

Tim Traveler · June 29, 2014, 12:59 PM

Hi Rick:

Thanks for the reply; I had not considered the condensation issue - I will have to look into that. I know exactly what you' referring to with the milky white crap. I am going to switch over to full-synthetic oil soon - I've read quite a few people's remarks on the cooler running temps. after switching to synthetic.

I've also seen some things online about different heat insulation wraps - like header wraps, I think - that seem to help as well. Thanks again and have a great day.

Tim

Tim Traveler · June 29, 2014, 01:23 PM

Thanks for getting back to me - these things are always having temp. issues. Mine did come with an electric auxiliary fuel pump that is mounted outboard of the frame rail, just behind the tank. It is plumbed in with 1/2" line and seems to run when only there is an extra demand for fuel. (I hope this is correct) I just took it's filter out and cleaned it (quite dirty) before my trip last week. Also changed the in line filter (dirty gas came out of this too) which is just ahead of the electric pump. Had a problem with the mechanical pump; replaced it last fall. It had trouble climbing the hill near my home until I changed the mechanical pump.

Last week I took it out for a 200 mile trip - it was running fine until I stopped for gas. Almost immediately after leaving the station, it began surging and hesitating. I attributed it to water in the fuel (something which should not happen at about $4.15 per gallon for super!) Put in some Sea Foam fuel stabilizer and dry gas and it smoothed out for awhile, but the problem returned. Am currently in the process of dropping the fuel tank to see if there's a pick-up filter in there - have had a similar problem on a different vehicle before. If nothing else, I suspect there may be dirt and junk on the bottom of the tank.

I have the 2 electric fans forward of the radiator, along with the clutch fan. You also mentioned removing the shrouds along the sides of the engine - are you referring to the straight pieces of sheetmetal mounted to the floor just above the upper A-arms? I'll give that a try too.

Thanks for all the help.

Tim

DaveVA78Chieftain · June 29, 2014, 03:43 PM

QuoteMine did come with an electric auxiliary fuel pump that is mounted outboard of the frame rail, just behind the tank.

There is a in tank fuel pump installed in the P30 chassis from 1985 1/2 through 1989. The component on the frame rail is a regulator. In 1990 GM went to TBI so the regulator is no longer needed but there is still a in tank fuel pump.

Per the Chevrolet Motor Home Service Guide, the shrouds were added to get more airflow over the exhaust manifolds and plug wires to keep the manifolds from cracking and the wires from melting. GM recommends that they be there to improve air flow so it does not exit out side before it is suppose to. The manual is available for free in the members area.

Dave

Rickf1985 · June 29, 2014, 07:44 PM

You mentioned premium gas, that in itself will help to cause vapor lock. It has a higher octane but also higher volatility. you really do not need premium. At least I have never had any problems with pinging and the compression ratio is certainly low enough for regular.

circleD · June 29, 2014, 09:47 PM

What Dave said about the fender wheel panels sounds weird because it would trap the heat in but the manual shows the airflow issue. You might have to fab one for your passenger side though depending on the year. AIR FLOW/ AIR FLOW/ AIR FLOW IS THE KEY

Stripe · June 29, 2014, 10:00 PM

Didn't you do a write up where you fabbed one circleD?

Tim Traveler · June 29, 2014, 10:18 PM

Hi Rick:

I have been putting in premium gas because the stations I usually go to have the ethanol-free premium. I figured that it wouldn't be much different paying more for non-ethanol than it would be to buy enough additive to treat for it. My rig sits quite a bit, as is the case with many of them, and I have seen the problems caused by the ethanol gas.

In either case, how do any of us know what's really going into our tank when we fill up? All I know is that it was running fine until I put gas in it the other day.

Tim Traveler · June 29, 2014, 10:32 PM

Hi Dave:

So what I thought was an electric auxiliary pump is actually a regulator? That makes sense because it seems to run intermittently. I looked at the VIN just inside the driver's door, near the floor and it states that mine is a 1989 1/2, whatever that means. It must have been one of the last to have a carburetor, since 1990 began the TBI models.

I still have the shrouds attached - will more than likely keep them in place.

Still learning - thank you for the information!

DaveVA78Chieftain · June 29, 2014, 11:29 PM

Tim,
By becoming a member of the site you have access to a large number of manuals we have here. The Chevrolet Motor Home Service Guide is one of them (a GM publication) that I pulled the information from. You would also have access to Chevy service manuals. Well worth the small membership fee which is used to keep the site up and running.

Dave

Rickf1985 · June 30, 2014, 07:06 AM

If you have a picture of the engine with the shrouds I would like to see it. Seems nobody still has them.

DaveVA78Chieftain · June 30, 2014, 07:39 AM

Article starts on page 7-4 of Chevrolet Motor Home Service Guide available in the Member area.
There is an article here somewhere that someone constructed if I recall correctly.

Dave

legomybago · June 30, 2014, 10:47 AM

I think you need to check fuel pressure at your carb, and flow...Your pressure regulator could be restricting flow? Your electric pump could be week? Clogged screen on the pump pickup line in the tank? Old rubber fuel lines sucking air? ALL that needs to be checked.

Mr. T · June 30, 2014, 03:00 PM

Just for the heck of it, run your engine at idle for a minute of two, then shut down. Stick your head under where the mechanical fuel pump is located. Watch to see if you have a drip, drip of gas from one of the lines connected to the fuel pump. If you do, tighten the clamp, stop the leak.

If the pump is leaking, it is also sucking air giving the symptom you have described.

Don T.

circleD · June 30, 2014, 04:30 PM

Stripe, I was going to do a thread about it but cnc or newrvguy posted a pattern on how to make one and I never did. Im still looking for the material.

DaveVA78Chieftain · June 30, 2014, 06:28 PM

QuoteOld rubber fuel lines sucking air?

Doubtfull on a pressurized system with pump in the tank (no hose to suck upon).

Dave

Rickf1985 · June 30, 2014, 08:34 PM

Unless the pump is not working, as mine wasn't. That was the only way I got home, the electric pump did not work so it did not blow all my gas out the bad regulator. I fixed the pump circuit and all of a sudden I couldn't run the engine because it was pouring out gas.

Tim Traveler · July 02, 2014, 09:27 PM

My computer modem was acting up for the past couple of days, but now I can post on my progress. I have removed the gas tank and there is no fuel pump in it. I figured there wasn't one because there is only 1 wire going to it (gauge sender). Also, there's no filter in the tank. I suspected I'd find lots of dirt/crap in the tank, but it's surprisingly very clean.

I'm replacing all of the fuel lines (5/16" and 3/8" between the tank and mechanical pump) as well as the 1/2" lines between the electric fuel pump/regulator and the mechanical pump. Nothing was leaking, but all the lines are 25 years old, so out they go.

Am going to check the mechanical pump pressure after I get the tank all back in. The electric pump seems to be doing fine - I think its stamped 8 psi on the housing, and according to my tester, its good. Just taking my time and routing everything properly.

legomybago · July 03, 2014, 10:26 AM

QuoteI'm replacing all of the fuel lines (5/16" and 3/8" between the tank and mechanical pump) as well as the 1/2" lines between the electric fuel pump/regulator and the mechanical pump. Nothing was leaking, but all the lines are 25 years old, so out they go.

That is exactly what we had to do....Same system.

I ran our electric pump off a powered off/on manual switch on the dash, but the fuel we are buying now for some reason is so vapor lock prone, that we just run down the road with the electric always on. We initially thought our vapor lock problem was only caused by 90 to 100 degree heat outside (thats when it started), but it happens even on cold days too...

Stripe · July 03, 2014, 10:54 AM

Quote from: Tim Traveler on July 02, 2014, 09:27 PM
I'm replacing all of the fuel lines (5/16" and 3/8" between the tank and mechanical pump) as well as the 1/2" lines between the electric fuel pump/regulator and the mechanical pump. Nothing was leaking, but all the lines are 25 years old, so out they go.

Just make sure those lines are ethanol resistant. We all know how much ethanol likes to eat certain types of rubber..

circleD · July 09, 2014, 07:43 PM

I hate to say it but if your tank is still down take out your sending unit and clean or replace it i?? But at least everything will be done. That's what I'm doing now. Waiting on the sending unit and have already replaced all the rubber hose. I've also took advantage of the extra space underneath and did some wire brushing, cleaning and making new ground connections, traced some wires and wrote on them, then a little bit of paint

because I could and I have OCD
Sorry!! I only read the few replies above and its off topic. So did the ethenal free stuff work? W%

Oz · July 10, 2014, 10:39 AM

I'm no mechanic, but from what I've read here over the years, the fuel lines and pump, in this case, could all be related to the apparent vapor lock issue. It's at least a natural progression of "fix one thing, find another one in the system". If it got too far off, then I'd split it and start a new topic.

It's an interesting and very informative read, that's for sure!

Tim Traveler · July 17, 2014, 10:13 PM

It's been a few days since I re-installed my fuel tank and replaced the mechanical fuel pump (along with replacing all the fuel lines, etc.). I took it out for a ride to put in some gas and to see how things worked. I went about 5 miles and everything was fine. A couple of days later (last night) I took it out again and almost didn't make it home. The engine was acting the same way it did before I replaced the pump - no power, would barely idle, almost didn't make the hill to get home - it acted like it was running out of gas. I checked the fuel pump pressure, and again, it wouldn't hold. (I have also checked the electric fuel pump/regulator and it pumps to 8psi like it's supposed to do).

This was the 3rd (and final) Airtex brand mechanical fuel pump I've had to install on this RV since last fall. I may have driven it just a little over 200 miles. Please, if you have to replace one of these on a 454 Chevy, DO NOT use an Airtex pump. There are many other online forums about these pumps, the problems that they have and how soon they fail. I have seen some other forums that show that the AC Delco pumps are about the best ones to replace an old pump with, so I'll try one of those. This job is way too much of a pain to do several times. I'm not sure if we're not supposed to use specific brand names, especially when speaking ill of specific products or companies, (if so, I apologize) but I would like to try to help save someone else a potential big headache.