I had a service shop tell me they did a cylinder balance test on my 89 150 302 efi multi port injected engine. Is this test possible on a port injected engine or does it only work on a sequentail fuel injected, because it is not bank injected? Any help with this explanation would be greatly appreciated

 

What they may be refering to is checking the compression ratio's on all of your cylinders to make sure that they are all with a certain percentage.

 

There is a cylinder balance test within the EEC computer as well. However, it is only on SEFI vehicles, which doesn't include the batch fire truck computers.

 

I believe that individual injectors could be disabled on a cyl-by-cyl basis to do the balance test when the EEC doesn't support it. You could also (for very short periods of time) disconnect individual sparking plug wires and monitor the idle rpm change. Balance tests are not new.
A more useful test would be a cylinder leakdown test, as there you have more idea of whence the leakage... of compression, that is..
tom

 

You are correct about pulling the plugs. I forgot about that method. The one on SEFI computers will do all the work for you and tell you what cylinder(s) is(are) weak, but it is still possible to do it manually.

 

It can be done if the shop has SBDS - a Star compliant tester will not show this. SBDS will measure the time between TFI pulses and detect minute changes as minute rpm changes, they will also cancel a cyl at a time and look for the aggregate effect on the motor.

SD or SFI systems - makes no diff to SBDS

 

Quad driver, it has to be an SEFI computer speed density or mass air, it doesn't matter, as long as it is SEFI. Trucks aren't SEFI, so this test isn't in the truck computer. It has to be done manually. What is SBDS? They'd still have to pull a plug wire or an injector to drop the cylinder even it the SBDS monitors engine rpm drop.

 

SBDS - Service Bay Diagnostic System, a very advanced scan tool developed by IBM for the EECIV computer to allow a user to see in real time the performance of every sensor and modify, simulate or dropout same.

As you know, a Star compliant tester only allows the viewing of codes and the ability to find out if a sensor reading is in range, the SBDS system actually communicates 2 way in real time. For the cylinder balance test (which I have done on EECIV machines, both SD and SFI - as I said it makes no difference) uses the PIP signal and a clip onto the #1 plug wire for a sync pulse and 'shorts' the targeted cylinders spark. The first thing it does is determine the CAW (crank angle word) for each cylinder by averaging the relative time between spark pulses, and then does the cylinder drop to measure the effect. After 2 minutes of this test it graphs the relative strengths of each cylinder in relationship to each other.

 

SBDS: service bay diagnostic system. A super-VOM with more stuff. Can monitor & change params inside the EEC-XX system. Supposedly, if you use the SBDS, you get less come-backs.. and it is 'guaranteed' to find what's wrong with your car. I don't think the $20+K machine actually lived up to its promo... But you sure can watch what's going on. I don't think it can stop the ignition from firing individual plugs, which indicates it cannot do the balance test for those vehicles...
tom

 

Does that hook into the computer harness like a break out box would? Quad driver, there can be speed density sefi computers; being speed density doesn't automatically make it batch fire (except trucks where Ford didn't use SEFI speed density). I see how it works now with the sbds. Thanks for clearing that up, and I'm sure it would be nice to have one of those in my possession .

 

It plugs into the diag port like the star tester, but the complete kit has harness adaptors to monitor or replace every single sensor connection in the engine bay - although Im not sure how many at a time it can replace. Problem is the sucker used to cost $50K to buy, but since EECIV has been out of print for 7 years now, many ford shops are ditching the machines. It would mean god status to find one on ebay.

 

You are very likely right, but if I were a dealer, I would think that unless OASIS(?) can handle the EEC-IV systems, it would be a little foolish to dump such an expensive machine whilst there were so many vehicles that it would help service... There are sill a bunch of EEC- systems out there. I have two... But things people do are not always what I would consider sensible.
tom

 

I ran into this exact problem - I had an intermittent power loss I could not solve with BOB or Star 2 so I called a local dealer and asked if they had SBDS, they said yes so I made the appt....I got there and it turns out they sold it, so I spent 2hrs and $70 talking to the tech and basically reproducing the tests I already did....never did exactly pinpoint the problem but I replaced the MAP and its a little better but I suspect injectors giving it up - something that SBDS would show. There is a potential for people not as familiar with EECIV wasting a lot of time/money at the dealer without...it almosts seems like they wanna claim 'well you have xxx miles on it, mebbe you need a new one, the old one is worn out'

 

FWIW, the fuel pressure regulators *can* flake out intermittently. I've heard that they can go nuclear or drop the pressure w/o sending an email ahead of time... But, they cost (some.. like 4.0 A*) over $100, so's it's best to use a fool pressure gauge taped to the windshield to see if that is the problem.
tom

 

WOW!!!!! thanks to all for all the information. I completely understand now how they use the sbds for a cylinder balance test. What a great site. Thanks again!!!