2000 Cavalier HPR Filter

[PaulReeder]

Hello All-
My 2000 bi-fuel Cavalier, which is still running so-so on CNG, has about 125 psi feeding the LPR, and that drops to about 110 psi upon engine loading. Also, the 1st LPR pressure port reads 3.0 psi . According to the manual, 115 & 4 psi are minimum, and, also according to the manual, I should first change the HPR filter.
So, what is a good source for the HPR filter kit?
Thanks in Advance,
-Paul Reeder

[siai47]

I wouldn't worry about either of the readings you have. The HPR's are all over the map. I have seen them with pressures as low as 80 p.s.i. static at the test port and the car runs fine. The range for the 1st stage of the LPR is 2-4 p.s.i. so 3 p.s.i. is right in the middle. The 15 p.s.i. drop you see is most likely line pressure drop between the HPR and the test port when you are asking for high fuel flow when the engine is loaded. This would verify that the inlet filter in the HPR is not restricting fuel flow. The 3 p.s.i. reading at the 1st stage test port verifies the low pressure lockoff valve and the 1st stage of the regulator is working correctly. The only thing left to check in the regulator circuit is a monometer check of the second stage of the LPR. Beyond that, what does the car do when it is running so-so on CNG I re-read all of your earlier posts and since your last one was in September, I was wondering which of the original problems are still with you.

[PaulReeder]

Hello siai47, how have you been? Thanks for the reply.
So-so = poor cold starting (Starts sometimes, other times not, even after the 8 seconds). If it does fire up, I can usually drive for a few minutes with a noticeable high idle speed. Not racing, but maybe ~ 1500 rpm. Come to a stop, engine dies. Restart is difficult, so I flip my handy cng fuse toggle switch (Not factory) and drive fine with gasoline. For the cold start scenario, I assume that the ECU has switched to closed loop. Not verified.
If the car is at operating temp (From gasoline), I can start wity CNG easily, and depending on the car's mood, drive quite well. No high idle, normal performance. But, it always eventually stalls when I come to a stop. I can sometimes restart it, but with honking traffic, I usually just flip my toggle and run on imported oil.
Also, I have gotten the P0171 code (Fuel trim System too lean). The manual says the fuel system is at full rich and still getting lean reports from the O2 sensor. One cause listed is "Incorrect CNG Fuel Pressure". Hence my post.
According to the manual, the 1st LPR port should be 4 to 6 psi. Perhaps you are correct that it doesn't matter, but I would still like to replace that HPR filter.
As noted by you and others, the scan tool is invaluable. I don't have one. Did I see some posts about PC software that will see the AF ECU?
BTW, I picked-up a 2004 Cavalier Bi fuel with a bad engine, so I will be selling the 2000. Basic car, looks good & runs well on gasoline. 57K. Any takers?

[siai47]

The reference that I use for most of the specs I refer to here come from a GM service information DVD published in October, 2008. I also have some printed manuals and supplements. I only have the DVD with me so I can't check it with the printed materials for accuracy. However, the SI shows 115-220 for intermediate pressure at the test port, 2-4 psig at the regulator primary test port and a 2-5" water column at the secondary test port. Your problem could, in fact, be a bad O2 sensor. The P0171 code can sometimes set after a long deceleration. The cold start problem you have usually doesn't relate to the hot running problems you are having. Usually hard starting is due to leaks in the intake system and the CNG isn't being pulled into the engine or the possibility of the LPL not opening during cranking. The high idle speed is puzzling unless there is a leak in the intake system on the engine side of the throttle body or the idle air system is messed up. I think you will be much happier with the 2004 after you get it running. The Ecotec engined Cavaliers use the RPO L42 engine which has different valves then the standard engine among a couple of other things. When you are rebuilding the engine try to save and re-use the cylinder head components.

[PaulReeder]

Thanks again for the reply. I replaced the O2 sensor some time ago, due to incorrect voltage readings (Key on, not running). The voltage reading was within range after replacement, but still the car is "So-so".
My source for info is the printed bi-fuel supplement. I'll try inspecting the intake system again for leaks. Also, where would you get that HPR filter kit?
Your comment about the engine differences is not what I wanted to hear, but graciously accepted. I thought the mechanicals were the same as the gasoline only version. What is your source for that engine info? Obviously I need to do more homework. I was going to swap with a junk yard engine.
The '04 is driveable, but the knocking rod (I believe) is not long for this world. But wow, what a difference. Starts right up and behaves like it was on gasoline. That's the CNG experience I'm after. But what an uphill battle it is.
Thanks again.
-Paul Reeder

[siai47]

I am pretty sure that part # 52368706 will get you the filter kit for the HPR. The "03 and newer Cavaliers also have a second filter part # 52371212 located next to the HPR as the fuel injectors don't like any crud running through them. The CNG Cavalier is made up of two RPO (regular production option) numbers. KL6 and L42 with KL6 referring to modifications to the car itself and L42 referring to modifications to the engine. All engines that run on CNG have higher exhaust gas temperatures which require valves and seats that will handle the higher temperatures without failure. These are more costly and are not used on the standard engines. The other modifications to the L42 basically relate to the intake manifold area and the mounting of the secondary fuel rail for the CNG injectors. If it was my car and it just had a rod knock, I would overhaul the engine that is in the car. You could either have the short block rebuilt or have it exchanged for a rebuilt. I would have the cylinder head overhauled -- valves and seats ground, valve guides and camshafts checked for wear (running out of oil doesn't help these parts either), install new valve guide seals and have the head resurfaced. If you need any valves and/or seats replaced be sure to use the correct parts from a dealer for the L42 engine. I would inspect the condition of the CNG injector adapter plate which looks like a big intake gasket. It should be reusable but if necessary, it is still available from the dealer. It would also help to own the 2004 alternative fuel supplement GMP/04-J-AF-1. www.helminc.com used to have them--I haven't checked lately to see if they still do. Your reward for fixing the newer car will be well worth the effort. They start and drive much better then the older fumigation system cars, have way more horsepower and better fuel economy. Now if you could only get a CNG Cobalt ----

[PaulReeder]

I'll get that filter kit and see what happens. I will post results. The '04 work will not start for a few weeks yet. No room in the garage. One project at a time...
Thanks againf for the advice. I see you're in Michigan. I live in a suburb of Columbus, Ohio. If you are in the neighborhood, your more than welcome to stop by.

[PaulReeder]

Hello Again-

Yes siai47, you were right, the HPR filter made little difference. Occasionaly, I do let the 2000 warm up on gasoline and then I switch to CNG and it runs pretty well. But I think I'm done with that car and will sell it as-is when (fingers crossed) I get the 2004 in good order.

That said, I'm starting on the 2004 now, and If the head and its components check out OK, I was going to get a salvage 2004 Cavalier (non CNG) engine and swap out the bottom end. I understand the exhaust valves and other top end parts are CNG specific.

Whaddayathink?

[siai47]

There are some differences between early and late Ecotech engines--try and find an '03 or '04 donor motor. The crank position sensor wheel on the crankshaft in early engines has a different number of slots on it and will not play well with the PCM on the car you have if you get the wrong one. If it were me, I would look over the short block of the engine you have and have the crank turned and re-ring the engine and call it a day. That way you know you have the correct short block and it has new rings and bearings.

[dmb5]

Need to replace HPR on 01 Cavalier. The Impco HPR 3600 appears to be a close replacement.
However, images from the vendor raises questions that may be answered by those who have performed the replacement.
On the original HPR in the vehicle and in figure 10 on page 11 pictured in the hpr 3600 installation.pdf may 7, 08 rev 0 by dovh49 shows a seal, filter spring and adapter that screws back into the new HPR inlet side stub as it appears has been done in the refitted HPR seen in figure 11.
In the image of the new HPR 3600 provided to me by the vendor it shows a flat faced threaded inlet stub and no apparent recess that would allow one to reinstall the filter spring and adapter. It seems as though a union and threaded for-seal with oring channel would need to be installed.
Has anyone else experienced this?