Vacuum System 1988 Dodge Dakota 

If you have an 87 Dakota, this layout may not help you as much. The first 87 Dakota had some sort of two barrel carburetor stock, the TBI was a more expensive upgrade option. I remember looking at the vacuum diagram for the carburetor years ago and it was much different than the TBI with even more vacuum lines. But if you have money to spend to get the truck in good order, I would suggest ditching the engine and transmission and installing a later Magnum V6 with the 4 speed automatic transmission. Parts availability is much better, you'll have fewer headaches with the vacuum system, have much more power (125hp vs 175/185hp on the Magnum) and get way better fuel economy. If you have an automatic Torqueflite 904 3 speed, it kills gas, I get 15/16 mpg on mine. To put it into perspective how hard parts are to get, it took me two years to find an intake manifold for it. The passenger side exhaust manifold is unobtanium, as is the Y pipe. So when you start having exhaust leaks, you have to live with them. There is some commonality with internal engine parts with the 318, except for the crankshaft, but that's not at all helpful since the external parts are so hard to find.

@@GGigabiteM Hi Gigabite. I've been working on the truck slowly making it better. How's your truck treating you? Right now I'm trying to change the power steering hose. Ever have to do this? The old hose on the '87 has a longer nipple. Maybe 12mm long. The replacement has a 7mm nipple. I'd just try the new part except that I could only get one of two sides of the old hose off. I'm curious if you did this and if you maybe ran into the same issue with the replacement part not looking like the old part. Thank you.

@@surfreadjumpsleep Mine has problems. Rear main seal leak and front crank seal leak. Too hot to mess with changing them right now. I had to change the high pressure hose on my power steering pump several months ago because the rubber line split. Bought a replacement hose from O'reillys and it was wrong, the bends on the hard line were 180 degrees off, so I had to do some creative bending to get it to work. I would recommend just taking the old line to a hydraulic shop and pay them to make you a new correct line, so you don't have to fight with chineseium garbage.

@@GGigabiteM But you didn't have to change the nipple? you could tighten it in there without leaks? Is your new hose's nipple shorter than the old one? (that sounds just terrible but I think you know what I mean). I could post a photo to show you what I mean. You need a lake or something to go dive into. I wish it were hotter here so it would be warm enough for the lake.

@@surfreadjumpsleep I don't remember if the fitting was the same depth or not. It shouldn't be too critical as long as the metal flare/flanges bottom out in the hole. The thing that makes the seal is the metal on metal, not rubber. The only thing the O ring will be doing is keeping the flare/flange centered and stopping low pressure leaks. Rubber seals can't be used on power steering systems anywhere. They'd be blown apart by the 1000PSI+ pressure on the high side, and attacked by the corrosive power steering fluid anywhere else. There are synthetic polymers that are used for seals on power steering systems

There are three vacuum connections on the brake booster. The large one on the side is the vacuum source from the throttle body. The small port pointing up goes to the optional cruise control module. The port on the front goes to a vacuum line through the firewall on the lower left of the brake booster to the climate control head in the dash. On the inside of the cab, it's somewhere above and behind the gas pedal on the drivers side. There's another vacuum line that goes back out the same hole in the firewall to the heater control valve in-line with the upper heater hose to the heater core. If these two lines are broken, your vents won't work and will dump to the floor and defrost vents.

Need to know where the sound is coming from. A hard shifting transmission can make clunking noises, but generally only does so when shifting gears. If the clunking happens when braking or slowing down, you might have bad driveshaft U joints. You can check this by going under the truck and rotating the drive shaft back and forth by hand and checking for any play in the joints.

That vacuum port comes off the brake booster, if you do not have the optional cruise control module then you must cap that port off. They make proper vacuum caps to cap the port off, but I found that they dry rot and start leaking quickly and I got tired of replacing them. If you do like I do, just cut a small section of vacuum hose and fill the end about a quarter to half inch with hot glue, it's best to roll it slowly on a table while filling the end up and then put a small cap on the top to prevent the plug getting sucked in. Don't apply it while on the vehicle, if you get hot glue inside the brake booster, you're going to have an expensive problem. Symptoms of a vacuum leak on the brake booster are a squishy brake pedal, or the pedal sinks all the way to the floor. Another symptom is the engine runs like crap, if you fix this leak and the engine still runs poorly, you probably have other vacuum leaks that need to be fixed. There is a second vacuum port for the A/C system which goes through the firewall below and to the left of the brake booster, you can access it from the cab by looking above the gas pedal. You'll also want to make sure these lines are not leaking or it can cause the same problem.

You may have just helped me a TON! Because my brake is squishy and doesn’t completely stop when pushing brakes and the engine seems like it hasn’t been performing at full potential. Thank you!

If you've never changed the brake fluid in the master cylinder, you may want to do that as well. Wipe off the two caps on the master cylinder and remove the cap closest to the firewall. Take a turkey baster and touch the end to the bottom of the reservoir and suck some out. It should either be clear or a light amber color, if it's dark brown or black then you need to suck all of the fluid out and replace it with fresh DOT3 brake fluid. If it's green then you have significant amounts of water in the brake system and should consider getting the brake system flushed. If you do have bad fluid in the reservoir, keep replacing it regularly at weekly intervals until it stays clean, brake fluid in the system tends to migrate around and will eventually mostly clear up. Another thing you should check is the transmission fluid and filter, which is one of the most commonly neglected maintenance items. The transmission dipstick is on the left side of the engine behind the exhaust manifold if you have an automatic transmission. Good fluid should be bright red, if it's brown then it should be changed ASAP. If it's black or black and you can see glitter in it, then the transmission is damaged and you'll have to make a decision. Either drive the transmission until it blows up or changing the fluid and risk transmission failure. Transmission fluid should be changed every 30,000 miles or once a year if you don't use the truck as a daily driver. The differential gear oil should also be changed in a similar interval.

Depends on if you have a carburetor or a TBI. The vacuum port on the side of the "vacuum tree" is much larger and allows a higher vacuum to be pulled, assisting the brakes more. If you have a carburetor, I have no idea what the vacuum connections look like on it or the intake manifold. The port on the front should connect to a vacuum line going through the firewall that drives the vacuum actuators on the blend doors on the air box. The top vacuum line is for optional cruise control. Have you checked the calipers, rubber brake lines and rear shoe wheel cylinders? Bad calipers, wheel cylinders and collapsed rubber lines can cause the brakes to not work also. I had one of the front rubber brake lines collapse awhile back and had to replace both lines. If the vehicle has an unknown history, the safest thing to do would be to replace everything so you have a known good starting point.

The truck is carburated. The vacuum line looks like it goes to the base of the carburettor on the firewall side

I have pressure until I start it and the pedal goes to the floor

Forgot to mention so far I have replaced wheel cylinders, shoes, master cylinder and booster. I have checked and no fluid leak anywhere, no air in the lines

@@dpkdpk1963 >I have pressure until I start it and the pedal goes to the floor If you've replaced everything, including the brake booster, it sounds like you have a bad vacuum leak or no vacuum at all. I'd pull the main vacuum line off to the brake booster and see how hard it's pulling while the engine is running. You should be getting a good vacuum at idle and the full RPM range. If you aren't getting a vacuum, or have a weak vacuum, something is wrong with the intake or carburetor. The engine should be running very poorly if there's a bad vacuum leak. Mine with a TBI acts like it has multiple dead cylinders with so much as even a pin prick of a vacuum leak. The 87 is even more of a unicorn than the later 88-90, because it was the only model with a carburetor standard, optional TBI. Every later year had a TBI standard.

Not sure. The first gen dakotas use a round connector on the fuel sending unit with 4-5 pins. At some point, Chrysler changed to an oval style connector, making them incompatible without having to chop and rewire the harness. When my fuel pump went out several years ago, I opted to just replace the fuel pump and pickup screen in the sending unit so I didn't have to modify the wiring harness. If you can rebuild your existing sending unit, I'd recommend it, because there's also the issue that the resistance on the fuel gauge float could be different, which would throw your dash gauge off.

Yes.

The climate control box is one big box that contains both the heater core and evaporator core if you have A/C installed. There are several vacuum lines on it that control three different vacuum actuators if I remember correctly. One is the blend door, one is the recirculate door and another is to control where the air goes to the vents to the floor, the dash or defrost. I don't remember off the top of my head which vacuum lines go where, I did that job several years ago and didn't take too many pictures of it. I do know that all of the vacuum lines on the climate control box go to the A/C head module in the dash and they're color coded. I may have a picture of the top of the box somewhere still that might show the positions of the vacuum lines, I'd have to go look.

I dug around and this is the only picture I have of the top of the air box: i.imgur.com/FyyNX5W.jpg Not sure if it is helpful or not.

The Tee pipe that bolts to both exhaust manifolds doesn't have a check valve in it. I've had the whole Tee pipe off of my truck once a long time ago, and I don't remember there being any check valve in it at all, it was just a straight pipe with a branch going off to the smog pump. Unless you mean the vacuum actuator that sits on top of the smog pump? That thing shouldn't have carbon or even oil in it, all it does is get air from the smog pump and blow it back through the exhaust. If you have a fouled up air line with carbon, that'd lead me to believe your engine is running extremely rich, and maybe a severely restricted exhaust system. It almost sounds like you have a clogged catalytic converter and the engine is trying to push exhaust out anywhere it can, one path being back up out the smog pump lines. I would need to see a picture of what you're talking about, because threads on whatever you're talking about doesn't make sense.

@@GGigabiteM Yes it's the the pipe that branches off that runs to the air pump. That's the one I'm talking about lol I wish I could post a picture on here. I would show you what it looks like

Is there a way for me to get a picture to you? Also, how do you know if your catalytic converter is bad?

@@jadepolky3805 You can try putting the picture on an image sharing site and linking it here, but there's a good chance it will get filtered. Always worth a try. Either that, or make a short video and upload it to YT and I can see it through your profile.

@@jadepolky3805 The symptoms of a bad cat are bad fuel economy, poor performance and difficulty starting and stalling. Problem with those symptoms is there is about a half dozen other things that can cause those same problems. The easiest method is to just remove the catalytic converter and look at it. It's a pain in the arse to do, but you probably need to replace it regardless since it's 30+ years old. They're consumable items, they wear out over time. Hopefully you don't have the California model, which has three cats. One on each down pipe in addition to the one at the end of the Y pipe. I need to replace the cat on my truck because it's rusted out, just haven't had the time.

>Where would you start with a problem like this? Thanks in advance, if you dare to even guess at this. Don't start jacking with the jets, those are the last things you should be messing with. Check the ENTIRE vacuum system first and make sure you have zero vacuum leaks. Even a tiny pin prick of a vacuum leak will cause run issues. The 1st gen Dakotas have dozens and dozens of vacuum lines, so you have a big task ahead of you. Check the vacuum lines for cracks or poor connections on tees and unions. If you got a bunch of vacuum line stuck together with unions and tees and tape and shit, take all of it out and make the simplest possible runs to where the lines need to go to eliminate sources of leaks. Document where the lines go and tee off to the different places so you don't put a vacuum line in the wrong place. Also remove the EGR valve on the drivers side of the engine and check to see if the passages in the intake are plugged with soot. If they are, vacuum the crap out and clean out the EGR valve. The metal line that comes off the side of the valve is also subject to getting plugged, you'll need lots of brake cleaner and some dollar store pipe cleaners to clear it. I don't know if the 87 has a PCM like the later TBI models do, but if you have an oxygen sensor on the down pipe, change it. A bad oxygen sensor will cause the engine to stall and die if there's any computer control of the engine. As for the carburetor, if you've never seen the inside of it, and its history is unknown, you'll probably have to tear it apart and clean it. Carburetors are almost never cared for properly, and if that truck sat for any length of time with fuel in it, especially ethanol fuel, the inside is probably horrible. I'd guess it has jellied fuel, rust and corrosion all inside the float bowl, and the jets are probably gummed up too. Rebuilding a carburetor is indeed a challenging task due to all of the parts inside. But if you take lots of pictures and document where things go when you take it apart, it will go back together properly. But only when you have eliminated all possible vacuum leaks from the system can you adjust the jets, because it requires a vacuum gauge. If there's any vacuum leaks, it will throw the gauge and fuel mixture off, and you'll either flood the engine or starve it for fuel. One other thing I forgot to mention is that the intake manifold is subject to becoming clogged. I would suggest getting a cheap boroscope, removing the carburetor and looking down all 6 intake passages. If you see any of them being restricted, you'll need to take the intake off and clean it.

@@GGigabiteM Thank you Gigabyte for all this great information. I'll start with the vacuum system then as it sounds way easier than the rest. My mother's offer of a free toyota corolla, just need to drive it from atlanta to maine sounds better & better though. I'll try the vacuum lines but the rest of it sounds like it would take more time than making that 1300 mile trip.

​@@GGigabiteM btw, is the big thing that attaches to the top of the valve cover on the passenger side part of the vacuum system? It has a hose that goes to the air filter compartment. Because the hole it fits in seems somewhat loose.

@@GGigabiteM Just to summarize the basic situation, correct me if i'm wrong please: the carb is controlled via the engine's vacuum. And so if there is a leak anywhere in the vacuum system, the carb won't function properly and you'll have the same sorts of issues like i was describing?

@@GGigabiteM Some great info in this: "On the vacuum line that routes to the ESA check the tee and its line that goes to vacuum controlled orifice tank vapor valve and see if that is leaking. The diagram shows a 1/2 inch hose that routes from the base of the carburetor towards the rear of the engine. It connects to a tee. One leg of the tee goes through a filter and onto the brake booster check valve. The other leg of the tee goes through a filter and connects to the vacuum amplifier. Disconnect the hose at the brake booster check valve and plug the end so there is no vacuum leak. Disconnect the other hose at the vacuum amplifier and attach your vacuum gauge. See if you get 16 inches or more of vacuum. If no then you will need to trace this hose back to the carburetor and also the brake booster vacuum hose from the booster back to the carburetor. My experience with vacuum hoses is that those that are closest to the carburetor or throttle body (heat source) will harden and lose elasticity. With no elasticity they will start to leak but from a casual glance appear to be in good condition. If you find the hoses attached to the tees are hardened you will have to be careful in removing the lines as the plastic tees will become brittle due to heat and are easily broken."