1980 Scottsdale Diesel to Gas Conversion?

[Cars662]

I have a 1980 Chevy Scottsdale pickup with a 5.7L diesel engine with a 350 (I think) auto transmission. I haven't looked at the stamped numbers or tags on the trans yet, so I'm not sure about the trans size. The block and everything is basically the same as a 350 gas engine, and I was told it's a 350 trans. I can check that any time if I need to. I am tossing the idea around of converting this truck to a 350 gas engine. I haven't had much luck finding someone in my area who can work on this beast. The injection pump has been completely cleaned and rebuilt. I put a new timing chain and gears on and set the timing myself, as the first mechanic gave up and disappeared. I'm not sure that I have the timing set correctly, on the engine and/or the injection pump timing settings. Right now, I have the truck in a local shop. I want to have the compression, fuel pressure, and glow plugs tested before going any further. If any of these tests fail, I will definitely go to a gas engine. If the tests are ok, I will get the truck home and try to crank it again myself. If it doesn't start up after that, I will go forward with the conversion anyway.

• What is involved with this conversion? I know I'll have to find a way to drain and clean the fuel tank, but what else am I looking at here? Will this conversion be worth my time, and will it be expensive? What advice can any of you guys give me before attempting this conversion?

Thanks in advance for your assistance!
Dale

[Mark Rinker]

Hello and welcome!

TDP is made up of GM diesel enthusiasts - here you'll find the deepest knowledge of how to troubleshoot and repair your diesel.

Don't give up just yet - your truck will be worth FAR more with the diesel engine, and the satisfaction of many many more troublefree and economical diesel miles are only a few answers away.

Search the forums, ask questions, don't throw in the towel just yet!

[convert2diesel]

Dale:

First things first:

1. You will find a timing mark on the front flange of the injection pump and there should be a corresponding mark on the engine side. Match these two up. This will at least get the engine started. You can play with the timing later.

2. Remove all the glowplugs. Note: these were the first generation of plugs, so you may have some that are swollen in the prechambers. Don't under any condition try to pry these out as breaking off the tip will mean having to remove the head to get it out. The injectors on these engines are too small to get them out that way. You might have some luck by backing out the glowplug till you run out of thread, then crank the engine over a few times. This sometimes blows the plug out of the head.

To test the plugs, wire up some 12 gauge wire and connect each plug (positive to the terminal and negative to the body of the plug) Wear gloves as these get hot very quickly. It should only take about 7 seconds for the whole tip to glow red. Any more, or if only part of the tip glows, then replace the plug.

3. With all the plugs out, loosen off the fuel lines from all the injectors and having first detrmined that you have power at the shut-off solinoid (top of pump, front conector), crank the engine till you see fuel at all the injectors. Tighten up all the fuel lines and crank the engine till you see a nice cloud of fuel air escaping out the glow-plug holes. Replace plugs, re-charge the batteries and she should fire off immediately.

Back in the day, I was able to buy alot of these engines cheap because of fuel pump replacement and mechanics not knowing how to bleed the system properly. They were a bear to bleed so few of the quick tricks worked. You had to go through the whole process.

Don't give up too soon on this. Being a 1980, more then likely, the engine has been replaced with a GM warrantee engine. The first generation of these engines really had their problems. In 1981 GM came out with the "DX" block with a roller cam, stiffer bottom end and longer head bolts. Check both sides of the engine just above the motor mounts. "DX" will be cast into the block on one side of the other (can't remember which side). The DX engine was really a decent engine as long as you didn't expect too much out of it. The major benifit was the fuel mileage. I have had four full size cars with this enigne in it and they all gave me 40 MPG (IMP)/33.5 MPG (US) on the highway in 4,500 lb. cars!!!! After 81, any resemblance to a gasser was purly coincidental. This was a true diesel.

They never really solved the problem with the heads mind you but as of three years ago, you could still get replacement heads fairly cheap. ARP still lists a stud kit for this engine as opposed to GMs "torque to break" bolts and Felpro makes a solid copper gasket for it. Once this is done, starting the engine properly and letting it warm up before putting your foot into it, will give you a long life for the heads.

Good luck. There are so few of these originals left, don't destroy it by putting a gasser into it.

By the way, you probably have a 350"C" (lock-up convertor) tranny in this. Was a popular tranny for this engine.

Bill

[Cars662]

Thanks, Bill. That's great advice. I would much rather keep the diesel engine. I'll give this a try and let you know how it's going, or ask more questions if I have any.

Thanks!!!
Dale

[DieselDavy]

Dale,
Bill is giving you good advice. This is a decent engine. I've had several also and I love them. Probably the best cold starting diesel engine I've owned. Great mileage!
There used to be another diesel web-site dedicated solely to 5.7L. I'm pretty sure he is a member here. Maybe he'll jump in here or Jim can direct you to him. Here is another place to get some info. (http://a350diesel.tripod.com/v8-1.html)
Keep working on it. You'll love it!
Dave

[Cars662]

Thanks, Dave. I have decided to have the truck towed back to my carport later this week and get it cranked. I know the benefits of a diesel, and I want to keep the diesel if at all possible. I'll follow Bill's steps to getting it cranked and running well again. I'm sure I will have more questions later. This engine ran great before, and the guy that rebuilt the injection pump said that he set it to increase horsepower. I was getting great MPG and I am willing to sacrifice a few for the gain in power.

I didn't mention this in my original post, but the first tech wired an electric fuel pump inline before the new filter canister. I don't know if this was a good idea or not? It is switched power. Will I still need to go through the steps to bleed? I thought about trying to prime through the intake with fuel. Would that work?

I am looking forward to hearing this engine chatter again!

Thanks again guys!
Dale

[Edahall]

I didn't mention this in my original post, but the first tech wired an electric fuel pump inline before the new filter canister. I don't know if this was a good idea or not? It is switched power. Will I still need to go through the steps to bleed? I thought about trying to prime through the intake with fuel. Would that work?

I am looking forward to hearing this engine chatter again!

Thanks again guys!
Dale

The wired electric fuel pump does make priming a bit easier but you'll still need to loosen each line that goes to the injector and run the starter until fuel starts coming out. Once that happens, then tighten the fittings and try starting it. Make sure to only run your starter for a short period of time and let it cool down before trying again. Also, make sure the electric fuel pump is wired up and working.

Power can be increased a bunch with some extra fueling and better exhaust / breathing. You might look into headers for this rig. It's possible regular 350 headers might fit.

[Cars662]

OK. I loosened the fuel lines from the injectors, and turned the engine. There is a small amount of fuel dripping from a couple of the lines, but not all of them, and it has no pressure. As Bill suggested in Step 3 of his post, I made sure there is power to the shut-off solenoid on the front of the injection pump. I took a pic to post here. I want to be sure this is the correct connector. The red (looks orange) wire in the pic has power. The green one doesn't have power. http://yfrog.com/e788111275j



As for the fuel pressure..... I installed a new box filter, located behind the injection pump, and there is a new canister fuel filter also. The injection pump had so much crud built up in it. The pump rebuild cost me $850 so I wanted to be sure this never happens again. Could the filtering be making it hard to build pressure or to prime? Thanks again, guys!

Dale

[convert2diesel]

Dale:

Yes the red(orange) wire is the one that must be live. With a cold engine, the green should also be live as this is the cold start advance. Having power to the green will make bleeding easier (de-pressurizes the dome). Normally this circuit is connected in series to a temp switch (turns off at 130 F) on the back of the passenger head. Advances the timing by 3-6 degrees while engine is warming up.

If your filter is plugged, then definitely it will effect flow. A trick I used on occassion if I suspected the rest of the fuel system was to remove the intake and replace the intake line with a flex line going to a five gallon can of clean fuel on the roof of the car. The IP will draw without a lift pump but I did start the syphon so that the fuel was at the pump. Re-install the intake (exhaust cross over in center of intake makes start up interesting with the intake off) and follow bleeding instructions through to initial start-up.

Fuel systems on these vehicles were always something one had to keep an eye on. Any leaks or restrictions cause problems.

Hope this helps.

Bill

[Cars662]

I connected switched power to the green wire. I do have fuel to the injectors now. Problem is, it is slow. I bypassed the canister filter. While I had the fuel hose loose, I checked that the electric pump is pumping strongly, and it is. After bypassing, I cranked the engine over and ran around to look under the hood. Fuel was dripping from the lines that are disconnected from the injectors. I placed a glass jar under one line and braced it. There was a small amount of fuel in the jar, so I know that I have fuel to the lines. But I don't know how much pressure. The sides of the heads are soaked with fuel. I know for sure that the rod on the mechanical pump is riding on the ecentric correctly.
Should the fuel be very strong flowing? Do you think the NEW box filter I put on there could be reducing the fuel pressure? What's the next recommended step?

Thanks!
Dale

[DmaxMaverick]

The actual volume of fuel at each injector is very small. If they seep, they're getting fuel. If it won't build pressure, the problem is with the injector pump. Even a very plugged filter(s) shouldn't prevent starting if you are seeing fuel at the injectors. Verify the glow plugs are heating. Even if it is way out of time, it should still fire if you get enough fuel into the cylinders. If the block heater is intact, warm up the block first (this should eliminate cold start combustion heat issues).

Be careful with repeated cranking with the fuel on. Enough fuel can build up in the cylinders the engine can run away for several (nerve racking) seconds. It's always best to remove the glow plugs and give the engine a few good cranks to clear them after a fuel soaking.

[convert2diesel]

The actual volume of fuel at each injector is very small. If they seep, they're getting fuel. If it won't build pressure, the problem is with the injector pump. Even a very plugged filter(s) shouldn't prevent starting if you are seeing fuel at the injectors. Verify the glow plugs are heating. Even if it is way out of time, it should still fire if you get enough fuel into the cylinders. If the block heater is intact, warm up the block first (this should eliminate cold start combustion heat issues).

Be careful with repeated cranking with the fuel on. Enough fuel can build up in the cylinders the engine can run away for several (nerve racking) seconds. It's always best to remove the glow plugs and give the engine a few good cranks to clear them after a fuel soaking.

All good advice. Pulling the glowplugs and cranking the engine with the fuel turned on will also tell you if you are getting pressure. You will see little vapour puffs out of the glow plug holes. Replace the plugs and you should have a start. Another thing to remember is not to run the starter for longer then 15 or 20 seconds at a time. These are heavy amp starters and they over heat quickly. Give it a 2 minute break between cranking sessions.

Bill

[Cars662]

UPDATE--
I removed the glow plugs and tested them all. All eight turn bright red in under 10 seconds. I cranked the engine over and watched for the vapor 'puffs.' OK, that worked, so I have fuel past the injectors. I reinstalled the glow plugs. Then I held the button to heat the glow plugs, turned the key, and the result...
http://www.megavideo.com/?v=BZZLYN8L
I have to say, I am impressed by the power this truck has, compared to how it ran before the injector pump went out. It has new timing gears and chain, fuel pump, and the injector pump has been rebuilt and cleaned. I hope to keep it running for years to come, and I will keep up with normal maintenance on this truck. In fact, the next step will be to change the trans filter. So, one more question for now.... How much fluid will the trans hold? 3 or 4 quarts if only changing the filter?
Thanks guys! For everything. I had almost given up on this engine ever running again. My business partner recommended I post on this forum, and you guys talked me through this job very well. Good job! I would recommend this site to anyone! Thank you very much for your patience, and your help! I really couldn't have completed this without all you guys' help!

Dale

[convert2diesel]

Dale:

They always sound best on the first start, especially if it has taken a bit to get them running. Before you do the tranny, make sure the HPCA (remember that green wire?) actually turn off after a few minutes. The engine will get quieter, smooth out and there will be a slight drop in RPM. Based on your short video, it sounds and looks as if your too far advanced. Contrary to popular belief, these engines are probably the smoothest running diesel you will ever encounter.

If my memory serves me correctly, the 350 hold about a gallon in the pan. If its has been awhile, you might entertain doing a "red neck" flush. Disconnect one of the lines going into the rad. Attach a hose to both sides and place both in a five gallon pail (makes sure you do both, if you only do one it will be the wrong one and you will have tranny fluid all over the floor). Start engine in park and run until the flow into the pail just starts to sputter. Turn engine off immediately.

Drop the pan and change the filter (the pan will now be empty). Re-assemble every thing except for your hoses and using whats in the pail as a reference, replace the fluid. You can repeat the first stage until the fluid comes out bright red and clean. Again replace the equivalent with new fluid, replace your tranny line and fire it up till warm. Recheck the levels and your done.

Bill