1985 C4 will crank but no start

My fuel system is as follows:

Tank and pump to
Fill line to filter
Filter back to fill line to engine bay into pipe that runs on top of fuel rail to the FPR

The return line comes out of the fuel rail end directly and returns to the tank

Is this right? It seems backwards to me from what I have read and researched. I thought that the fill lines runs INTO the rail, not to the FPR.

Even the two fittings in the engine bay are different sizes so, if this is wrong, I dont get it.

C

 

The feed line is supposed to go into the fuel rail itself at the front - NOT the gray line on top of the rail that goes into the FPR. That gray line is the return line.

Check your routing again carefully. On some years, the connections at the front are the same size and can be reversed accidentally. If they are different size on your year, then in theory it's not possible to reverse them.

The line with the fuel filter is generally the supply line for TPI motors.

 

Thanks. I have traced the lines and rechecked. My supply line that goes through the filter was tied into the gray line to the FPR. This is how I got the car. The connections on the front are NOT the same size. As it originally came it would not start and the fuel pressure measurement was 0 via gauge on schrader valve. I have checked it over and over and have no explanation why it is backwards. I was told originally that it would not run because of the computer and that it needed a fuel pump (both of which i replaced) but I am starting to wonder if it was not running for another reason.

I am in the process of swapping the lines so that the supply runs into the rail etc. This means new fuel lines and fittings for the connections.

Does this sound like I am on the right track in regards to this issue?

C

 

I'm not understanding how they swapped the lines previously. If your input lines at the fuel rail are not equal size, then the larger pipe is the Supply line and the smaller pipe is the Return line. The filter should only be on the supply line, which means that the engine side of that pipe should be the bigger one. Unless someone has swapped the input / output lines somewhere before the filter, the fuel pump should be supplying the line with the filter, and the filter line (thicker diameter) should be hooked up to the passenger side fuel rail. The smaller diameter line is the Return, should be hooked up to the gray pipe which bolts to the top of the rail. All this sizing info assumes you are running factory fuel lines, not some anodized / braided hose fittings that are aftermarket.

If somehow the lines are reversed, this is why you show 0 psi on the Schrader valve / gauge connection. The FPR is not designed to allow fuel into the rails via reverse flow, at least not easily nor at the right pressure.

You're sure your car only has one fuel filter right? The one that's mounted under the car on the right lower chassis rail? Or is it possible that someone else has installed another (second) fuel filter on the return line as well?

 

Yes the filter is located on the passenger side frame rail. All of what you said should be, i believe, is not on this car. The fuel lines are factory looking to me. I believe that this is the reason why the fuel pressure is 0. I do not see another fuel filter. I have seen multiple videos that demonstrate the anatomy in the engine. Of the two connections (R and L) as you face the front of the car, my original supply was coming into the L side which connects to the gray tube to the FPR. The connection on the R side was to the rail which should have been the return. I am in the process of moving them back to what seems the correct anatomy - - the opposite of what I have described how I found the car when I got it.

I have no explanation for how it was how it was.

C

 

Are you sure that the lines aren't reversed at the tank bulkhead? It is possible that someone managed to get the lines wrong during a fuel pump replacement. (Though I would imagine a difficult mistake to make.)

 

I understand what you’re saying. However I tested the fuel pump bulkhead and fuel came out of the app that’s on the top which would be 3 PM on this picture. Sorry it’s rotated. This is the one I took them out? Correct?


On this photo the top s at 3 o’clock.

 

This may (or may not) be helpful since I have the x-fire '84, not the TPI. but my understanding is when you turn on the ignition key to the run position the fuel pump starts and pressurizes the fuel line. When you start to crank over the engine the ECM is looking for a positive signal from the oil pressure relay to continue. If it doesn't get this within a brief delay time it will shut down the fuel pump via the pump relay circuit. I can't say if this is your problem, but it seems unlikely your fuel lines are mixed up or reversed. BTW, assuming the right side of your photo is the forward/front side of the car, that line at 3 o'clock is the high pressure fuel feed line. The line at 11 o'clock s the return.

 

[QUOTE=fredd1;1604663093] it seems unlikely your fuel lines are mixed up or reversed.

On second thought, the return line should be the one connected to the FPR (not the supply), which you mentioned in your original post, so that could be why you're reading 0 psi on the gauge. Strange that the lines were intentionally reversed though.

 

There's something here that doesn't add up Charles. You say in the first post that the two fuel hookup fittings at the engine are different size from each other. Factory-looking. This means they will only hook up to the right connectors on the fuel rail. Otherwise, if they are connected wrong (reversed), they will not bolt up or would leak like hell.

I believe you when you say that you've checked the tank side and the connectors are on the right lines. I believe you when you say that they fuel supply line appears to be going to the fuel filter. But if your lines are reversed somewhere, it wouldn't be at the fuel rail. It would have to be before there somewhere along the lines from the tank to the engine.

UNLESS, your fuel rail / fuel line connections are actually the Same Size. Then, in that case, they can be reversed at the engine. We have seen that on this forum a few times before.

 

I( have re looked at this many times. I am sure of the lines. I switched them and now I get fuel out of the line going to the supply entering the rail. In addition, when I flushed the return line from the tank, fluid came out the return line under the car (not the line to the filter; the smaller one) which is the return (it was exposed when I switched the lines back to where they should have been). Previously this was NOT the case. I have no explanation for this. Now my issues is that the fuel rail is not patent. Even though I get fuel squirting out of the line entering the rail the pressure at the schrader valve is 0. When I probe the rail with a small 16 g wire, i can only advance it about 10cm or so (estimate). So, i am tracing fuel to rhe rail but not down the rail. I think that the rail is blocked. Im planning to take it off the car and checking it better.

C

 

Where did you switch them?

 

I flushed both lines from the tank outlet. I made sure that I knew which one squirted gas when the fuel pump pumped. I made sure that the the supply line and return were identified under the frame rail at the filter. I then plumbed both lines with new hose back to the rail assembly making sure that the supply went to the rail and the return came from the FPR.

C

 

So someone had previously switched the lines at the fuel filter / frame rail area connection points, and that's where you switched them back to be correct?

 

Im not able to know what what was done. But, I think I did what you said. I certainly did nothing in the fuel tank area.

C

 

Ok Everyone, here is the result.

I stripped the fuel system down to the fuel rail and injectors, took it all off and installed new injectors. The fuel lines were backwards so I reversed them to their normal routes. Now the car starts.
So, my injectors were bad and the fuel lines that had been installed in the wrong directions at some point in time were backwards. This proves it. I dont know how it was done but it was.


Charles

 

Thank you for getting back to us with the cause / fix.