Hey there everyone.

New to the forum and wanted to see if anyone has ran into the same issue I'm having. I did try doing some research on the situation I'm having, but to no available.

I've got myself a 1979 XJ6 in-line 6 that I'm currently working on at the shop I work at. I recently swapped the engine since the original motor had a BHG. And it was a lot cheaper to replace it than to have it rebuilt. When my manager ordered the engine, it came from a newer model that had a different fuel line setup, EGR ports lines (?) next to the spark plugs, and water passage way. What I did, from the old block, I used the oil pressure switch, oil filter housing, intake manifold with water passage, deleted EGR port lines (?), and swapped flywheel into the new block. I've put everything back together and got it to run, sort of. Had to fix certain wires since how brittle they are due to age, and replace the injector box since it wasn't allowing it to activate injector #6. Once I got that going, the engine started to run a lot better.

Now, here is the situation I'm running into now. Every time I hit the gas pedal or pull on the throttle body lever, it sounds like it wants to shut the engine off. If I hold the throttle down in any position, it starts to run like crap and backfires into the intake manifold. I rechecked the timing on the distributor and its on point. I even rechecked where the plugs go from the spark plugs to cap. Is the firing order correct for this year model (1-5-3-6-2-4 in counter clockwise, & back by firewall 1-2-3-4-5-6)? I even replaced and adjusted the TPS sensor to no available. I made sure all the fuel injectors are firing and even replaced the sensor on the intake manifold that fuel goes into. I even swapped the MAF and it does the same. I'm really stumped and I feel like I'm about to give up on it. Any help would be appreciated it. Thanks everyone.

 

Why is a TPS on that engine???


Carl

 

Thats how it came with the car in the first place. Is it not suppose to have one? Does have a harness plug for it too.

 

Those are air injection tubes


Good work !



Backfiring into the intake generally suggests lack of fuel.

A couple quick things:

- Pull the fuel filter and empty the contents into a clean jar. What you see will dictate your next steps

- Check the ducting between the air flow meter and the throttle body. Secure and leak free?

- Is the bundle of black ground wires (5-6 wires) present an accounted for, secured under one of the bolts at the rear of the water rail? These are the grounds for the entire fuel injections system. Make sure you don't have a stray or two dangling in the breeze/



Yes on the firing order, yes on counter-clockwise.

#1 is at the rear



That's a throttle switch, not a throttle position sensor. On USA models is functions only at closed throttle and full throttle.


Good work, although confirming they are firing isn't the same as confirming they are fault free....but that a bridge to be crossed if we get to it

The fuel pressure regulator?

Just so you'll know, that's an AFM ---Air Flow Meter. A MAF is something different.

Nah, don't give up. People here will help.

Cheers
DD

 

Thanks for the help so far Doug. Really appreciate it.

 

Also, I forgot to mention, the fuel pressure with the engine running is at 35 psi. If I unhook the vacuum line to the pressure regulator, it jumps up to 45 psi.

 

Sounds right for fuel pressure.....which would typically suggest all's well with fuel delivery.

But .....

Just for giggles...it'll only take a few minutes... pull the new fuel filter and see if it's beginning to clog. It is very common on these cars to have tons of crud in the tanks....*especially* if they've say unused for long periods. Has this car been in storage, by chance? Also common for fuel pump to suffer from the crud. If the new filter is showing signs filling with crud again you may be zeroing-in on the problem.

I'll do some mulling on other possible faults but, if it was me, I want to be sure the possibility of cruddy fuel is eliminated before digging any deeper.

The blue injector thingy is the cold start injector. It operates only for a few seconds on a cold engine while the starter is engaged. If faulty it would cause a starting problem, not a running problem....unless it is dripping fuel into the intake manifold.

Cheers
DD

 

Here's a little story about the Jag we're working on. From what I've known, the owner daily driven the vehicle. Originally the car came in to the shop because it was having a starting issue. It'll just crank and would never start up. Then I figured out a black wire from the black relay on the firewall fell off so I placed it back in and fired right up. Then my manager noticed it was having a long crank before it fire up. So we did a leak down test and found out it was having a BHG deal. Could see bubbles forming out of the radiator. So that's when we decided to do the engine swap. But before we did the engine swap, it would take throttle sometimes, so it was intermittent.

Now that it idles perfectly fine, its starts acting weird for us to see the car not take throttle at all. Like it was lacking fuel (which is what we're diagnosing now). We did place a new fuel filter, but we took it off immediately and placed in a fuel pressure gauge. So at the moment, there's no fuel filter. If we spray brake cleaner through the AFM, it'll take throttle. But once the brake cleaner is out of the system, it goes back to not taking throttle.

Right now, we are waiting on a fuel pump and we're going to see if that'll help on the situation. We have no idea if its the original fuel pump or if its been replaced before.

 

We replaced the fuel pump for the heck of it since we have a new one sitting on the shelf and it didn't make a difference. Fuel pressure stayed the same and its still not taking throttle. This is starting to become a headache lol.

 

Bump.

Guess I'm stuck with the situation I'm having. I've done everything I could to get it to run right.

 

Maybe you better have a read of this: -

Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

 

This particular engine is not one that I ever messed with. Well, until I removed it.


But, You mentioned disabling the FPR by removing the vacuum line.
FP with vacuum was 45 psi. I don't think that should run things just fine. The pump should deliver circa 90 -100 PSI. And the regulator drop it to 35 or so.


I have my doubts that the unregulated PSI is adequate. As the new pump fares no better, and the filter is replaced. It seems that fuel lines are the next suspect.


And, perhaps the sock on the pickup tubes in the tanks are partly
plugged.


This and the fact that squirting brake cleaner makes it better confirms
inadequate fuel delivery. At least in my mind.


At present, my lump suffers from the opposite. Too much on revving. Black smoke at the pipes. Nevertheless, it runs great!!!
But, displeased the smog tech !!


Carl

 

From your original post: -

In the Roger Bywater article this is mentioned as caused by lack of fuel. So one or both of two things is happening: -

1. The ignition pulse is not widening to match an input from the MAF - maybe MAF needs looking at.
2. Fuel supply is not sufficient - yet you have checked the pressure is as per spec.

I'd have a look at the MAF. Checking these things is very difficult now, as all the old Bosch technicians are retired or dead, and nobody knows much about them anymore.

 

We never heard back regarding the new filter. Was it beginning to clog? Has cruddy fuel been eliminated as a possible culprit?

But, yes, let's revisit fuel pressure...... just for the heck of it and to make sure we're on the same page. You mentioned 35 psi when running and 45 psi with the vacuum hose disconnected. That sounds good, but how/where was this tested? The proper place is to disconnect the hose to the cold start injector at the fuel rail at attach your pressure gauge to that nipple.

As Carl mentioned the the pump should develop 70-100 psi 'deadhead' pressure. Since you installed a new pump it probably does...unless supply to the pump is restricted

Cheers
DD

 

Removing the vacuum line just defaults the regulator to the high side of its ability to adjust fuel pressure. With the hose disconnected the regulator won't adjust pressure up/down....but it's not quite the same as "unregulated".

To check the raw or deadhead pump pressure you'd divorce the pump from the fuel rail entirely. An easy way would be pulling the fuel inlet hose from the fuel rail and attaching the pressure gauge to it....then running the fuel pump. That's where you should see the 70-100 psi. That's the fuel pressure the regulator has to work with, so to speak.

Cheers
DD

 

It might be interesting to monitor fuel pressure *as the throttle is opened*.

You mentioned 35 psi with the engine running, and that sounds OK, but when you open the throttle does the pressure drop down?

It shouldn't.

Cheers
DD

 

Please describe exactly what you did here.

As mentioned, it's a throttle switch, not a TPS.

Cheers
DD

 

Doug:


Got it. My synopsis was too simple! Simplicity works at times, but not always.


But, all points to a fuel issue. At least that is progress. Dirty socks at the pickups still rings in my mind.


Carl

 

I'll give it a read once I have some time today.

I'll look into checking the sock. Is it easy to get to? Only tank that is working properly is the right side. The left seems to leak pretty bad when we added fuel. We didn't know till we came back to the shop after the weekend and boy, did the shop stunk like fuel lol.

Tell me about it. I used to know someone that was very good with Bosch products, but he disappeared into thin air.

 

Interesting. We still have the pressure gauge in place where the fuel filter sits. I'll remove it and place the pressure gauge to the cold start injector and place a new filter. I'll get back to you on this part.

Sounds like the fuel pressure is really pesky on these vehicles, especially where to check the amount of pressure.

I'll do this when I place the pressure gauge to the cold start injector.

I know lol. You mentioned it at the beginning of the thread. But yes, the switch on this on is adjustable since it has a slot to move it around.