Injection System Troubleshooting

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Injection System Troubleshooting

Postby JoeIsuzu » Wed Mar 18, 2009 11:05 pm

There's a "Frequently Asked Question" that goes something like this:
"Where can I get my injection pump overhauled?"

Of course there are lots of shops that will gladly take your money, and some will even do a good job with the overhaul...but at a MINIMUM of around $500 plus the time (or labor $) for removal and installation, it's best to FIRST determine if the pump really NEEDS to be overhauled.

One of our earliest members, Paul Moyer works in a fuel injection shop in Santa Maria, CA. Paul has worked it out with his employer to offer their rebuild service at a discounted rate for our members. He has also agreed to assist in putting together some troubleshooting steps "to illustrate the kinds of problems we see and what needs to be done to correct them."

With that intro, I'm turning this thread over to Paul. It will be locked, because it is intended to be a How-To guide, not a troubleshooting dialogue. If you have feedback or follow-up questions, please post them at the link below:
FEEDBACK: Injection System Troubleshooting...

Thanks, Paul, for taking this on!


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Re: Injection System Troubleshooting

Postby Paul » Thu Mar 19, 2009 1:08 am

EDIT 7.02.15 The prices for our rebuilds have gone up. Please see the edit in red near the end of this post. Thanks -- Paul


9.23.2018 - - Our price schedule has changed again due to increased costs and our experience with the Isuzu pumps. Please see the new schedule in blue at the end of this post. Thanks - - Paul


Hi All--

Jack has generously allowed us to offer our Isuzu P'up pump rebuilding service to the forum members in connection with a 'How To' thread on solving pump problems. By 'us' I mean Diesel Injection Systems of Santa Maria, Ca where I work part time, mostly on VE pumps.

Before I tell you about our service I want to emphasize that we do not want to talk anyone into rebuilding a pump. This work is expensive and if your trouble is caused by something else it is definitely best to make every effort to find that problem rather than rebuilding the pump and hoping that your problem will be fixed.

To that end Jack has made a special thread (FEEDBACK: Injection System Troubleshooting...) for you to ask questions and hopefully receive answers about your fuel system problems. When I spot a problem with a fix that seems of general interest I will post info on it in this 'How To' thread. Suggestions and help will be welcome.

Here are the details of our rebuild offer. We will do our normal rebuild for $500. This will include disassembly, thorough cleaning and inspection of all parts, needed replacement of parts which may normally be worn, new seals and test and calibration. If there are unusual parts in need of replacement we will get back to you with a new quote. An unusual part would include the Isuzu CSD and I am not sure if this is available. I will need to check on this and let you know. Also, the member will need to pay shipping to and from our shop.

In addition, because one common problem already identified with this pump is an internally leaking/sticky Cold Start Device (CSD) we have decided to offer a conversion to a manual CSD as used in older Volkswagen pumps. A pull cable will be required to operate this CSD and will need to be supplied by the member. Our price for a rebuild with this conversion will be $550.

Here is our contact info:

Diesel Injection Systems
1021 Tama Lane
Santa Maria. Ca 93455

Phone 805 925 1599 Ask for the boss, Larry Downum and tell him you are from the forum.

Since I am there only part time you should contact me by PM.


EDIT: 5.22.2009 -- Because we neglected to consider any extra cost for a turbo pump I want to point out now that we will need to charge another $50 for a turbo pump. This because it has a boost modulator which adds to both the rebuild and calibration effort. Total cost for a turbo pump will be $550. A turbo pump with the VW CSD option will be $600.


EDIT: 7.26.09 -- Our shop recently rebuilt a P'up pump for a customer in Southern California and I am attaching a photo of it. This pump has the VW CSD option added to it. Note that lots of the parts on this pump have been painted for appearance. We do not always do this.


EDIT: 3.01.11 -- We have found that the conversion to a VW CSD is substantially more work than we had thought. So, we have decided to raise the price for this feature to $100. Other prices will remain the same. This will make the price of a naturally aspirated pump with the VW CSD $600 and the price for a turbo pump with the VW CSD $650.



EDIT: 7.02.15 --

Forum members-- Costs have gone up for us so we regretfully need to increase the price we charge forum members for rebuilding Isuzu P'up pumps.

Here is our new price list:

-- n/a stock $550

-- turbo stock $600

-- n/a with Manual VW CSD conversion $650

-- turbo with manual VW CSD conversion $700



EDIT: 9.23.2018

Forum Members - - Due to rising costs and our experience with the Isuzu pumps we are changing our price schedule for rebuilding a pump as follows:

- - Either the n/a or turbo pump $600

- - The addition of the VW manual CSD to either pump $100



Frank's Finished Pump for Printing w cap.jpg
Frank's Finished Pump for Printing w cap.jpg (155.99 KiB) Viewed 7585 times
Last edited by Paul on Thu Jul 02, 2015 7:43 pm, edited 3 times in total.
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

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Re: Injection System Troubleshooting

Postby Paul » Thu Mar 26, 2009 1:07 am

OK, I am going to list a number of possible fuel system considerations with the thought of discussing them one at a time, probably in the order listed. If anyone has a suggestion for reordering the discussion let me know:

-- Fuel Leaks

-- Air Leaks

-- Static Timing

-- Timing Advance

-- CSD & Possible Effect on Timing

-- Injectors

-- Injection Pump

And a list of specific problems ( this could get very long):

-- Low Power :)

-- Smoking

-- Poor Mileage

-- Won't Start

And just so's everyone knows what an Isuzu injection pump looks like I am posting a photo. Note the arrow to the ID tag. A shop will need this number to look up the parts and calibration data for your pump.
Isuzu P'up Injection Pump '84 Right Side 600x450 c5.jpg
Last edited by Paul on Mon Mar 30, 2009 12:25 am, edited 1 time in total.
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

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Injection System Troubleshooting > Fuel Leaks

Postby Paul » Sun Mar 29, 2009 2:40 am

Both fuel and air leaks can occur at the same point but usually will not.

Fuel leaks will usually occur at a high pressure point in the fuel system such as the injection pump body or in the high pressure lines feeding the injectors. If there is a lift pump in the fuel tank or close to it there might be a leak from a fuel line. But, the factory P'up does not use a lift pump in the tank.

Air leaks will usually occur at a low pressure point in the fuel system such as the fuel lines running from the tank to the filter and then on to the injection pump. I will talk about fuel leaks in this thread.

Leaks in the fuel or return lines will drip or worse and you should be able to find the location by wiping off any accumulated fuel and then watching to find the location. These are usually cracked fuel line or loose clamps. Many times an old fuel line will crack first at a barb fitting. A fix (for a while) can be to cut the cracked end off the line and put it back. Note that most small fuel leaks will not cause any noticeable engine performance problem. So you sort of need to keep an eye out for leaks.

A leak in a high pressure line to an injector will cause roughness or a total missfire. These leaks should be visible. The source is usually a cracked line which will need to be replaced or a crack where the line is brazed into an end fitting. These can sometimes be repaired by cutting the line off and brazing on a new fitting.

Leaks in the pump are harder to find the exact location but if you will clean the pump and dry it off you should be able to see the location after starting the engine. Check out the photo below.

Leaks that can be fixed while the pump is still bolted to the engine are:

-- Throttle Shaft O-ring

--One of the two timing piston covers. The other one is against the block and probably not possible to get at.

--Housing Cover seal

--Head Plug O-ring -- But note that this will require a special triangular socket to remove the head plug. Also, it is best to replace a head plug once removed since there is a 'crush' feature on it to seal the high pressure pumping chamber.

Any attempt to replace seals should be preceded by a careful cleaning of the pump to avoid getting any dirt inside. The throttle shaft O-ring or the cover gasket will require that the cover be removed and there is a procedure for this. The timing piston cover is a common leak and I know some of our members have replaced these O-rings.

The remaining seals are the drive shaft seal, the head seal and the other timing piston seal and these will require that the pump be removed from the engine. There is a procedure for this.

At this point it is worth pointing out what many already know: If one pump seal is leaking, others may soon decide to do the same. These pumps are 25 plus years old and if they have not been rebuilt the seals are that old too. I have seen many pumps with seals that were hard, flat and cracked and most of them were leaking.

I realize this thread is a pretty sketchy re a 'How To'. So, if you have questions or want specific info please post in the following thread.
Isuzu P'up Injection Pump '84 left side 600x450 c5  .jpg
Last edited by Paul on Mon May 04, 2009 1:27 am, edited 1 time in total.
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

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Re: Injection System Troubleshooting > Air Leaks

Postby Paul » Mon May 04, 2009 1:24 am

Air Leaks will allow air to enter the fuel system and as it rises to the top of of the lines and cavities in the system the fuel will be allowed to drain back down into the tank. This includes the injection pump body. Problem here is that with the fuel level low in the body the pump cannot deliver fuel to the injectors and you will have a no start or at best a very rough start. Usually, air leaks are sort of slow and a restart in a few minutes or an hour or more will be OK. Overnight and longer is where you usually will have trouble to start.

You can confirm an air leak by temporarily replacing the filter to pump line with a piece of clear plastic line. Run the engine for a few minutes to see if fuel will run clear without any bubbles. If you have bubbles flowing through the line you certainly do have a leak. If the fuel is running clear you should shut the engine off and let it sit, say overnight to see if any bubbles or loss of clear fuel show in the plastic line.

Another way to check for this is to install a T with a vacuum gauge in the filter to pump line. Start the engine and you will see about two or three inches of vacuum. This is normal to lift the fuel from the tank and suck it through the filter. Now shut the engine down and you will see that about 1 inch or so of vacuum remains. Again, wait for a bit, say overnight and the vacuum should remain. If not, you have an air leak.

An advantage to the second method is that you will also be checking for fuel line and/or fuel filter obstruction. This will be indicated by a much higher vacuum reading, say 3 inches or more.

Finding an air leak is not as easy as finding a fuel leak as there may be no visible evidence such as dripping fuel. Best bet is to examine fuel lines for cracks or looseness at their clamp points. The fuel filter can be a problem, especially the plastic plug at the bottom. This has an O ring which should be OK since every filter comes with a new one. But the plug itself, which is plastic, is easily cross threaded. Be careful of this as the plugs are hard to impossible to find.

Auxiliary lift pumps are sometimes used to overcome air leaks as they will refill the system with fuel and purge any air back to the tank. I don't recommend these as they are another place to have a leak and the internal lift pump is adequate in this truck.

The primer pump on the fuel filter can also be used to refill the system with fuel to get you going. Trouble here is that many of these do not work any more, usually due to dirt being lodged under their check valves. This is not readily serviced because the top of the primer is crimped on the housing body. There is a way to fix these though and I have described it HERE.

Best thing to do with an air leak is to find the source and repair it.

I am attaching a photo of a T and a gauge that I use for this kind of stuff. However, any vacuum gauge, even one on a vacuum pump should be OK.
T & Gauge email.jpg
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.